Vol. 60, No. 5 (2011)



The theoretical and experimental investigation of repumping laser impact on cooling and trapping of strontium atoms
Chang Hong, Wang Xin-Liang, Tian Xiao, Zhang Shou-Gang, Gao Feng
2011, 60 (5): 050601. doi: 10.7498/aps.60.050601
Abstract +
We have conducted experimental investigations on the effect of repumping laser on the cooling and trapping of strontium atoms. More than 3.1×10888Sr atoms have been trapped with 679 nm and 707 nm repumping laser added. The two repumping lasers enhance the trappopulation by a factor of 17. We also made experimental investigations on the effect of 707 nm repumping laser detuning on the cooling and trapping of strontium atoms. The fluctuation of atom trapping population is less than 3 ‰ when the detuning from 707 nm is 5 MHz.


Relationship between liquid structure and property Ⅱ—— Kinematic viscosity of Mg-9Al melt and its relationship with the microstructure
Mi Guang-Bao, Li Pei-Jie, Охапкин А В, Константинова Н Ю, Сабирзянов А А, Попель П С
2011, 60 (5): 056601. doi: 10.7498/aps.60.056601
Abstract +
The method of crucible rotating oscillation damping is employed to measure the kinematic viscosity of Mg-9Al melt, and the curve of viscosity ν versus temperature T from 890 K to 1190 K is obtained. It is found that there is an abnormal change for the viscosity in the first heating process, i.e., when the temperature is increased to 1000—1075 K, the viscosity varies from increase to decrease. However, in the subsequent cooling process and the second heating process, the viscosity increases (decreases) monotonically according to an exponential law with temperature, which accords with the Arrhenius equation. Based on the residual bond model and the calculation model for evolution behavior of "average atomic cluster", the correlation between viscosity and microstructure of Mg-9Al melt is discussed. The results show that the breakage of Al-Al(B) bonds in basic unit of β phase-like residual bond structures causes an abnormal change of viscosity in the first heating process; in the subsequent cooling process and the second heating process, the melt reaches a new dynamic equilibrium state, and Al atoms are uniformly distributed in the melt. At this time, the size of Mg-Al average atomic cluster dS and the number of short-range order atoms NS inside them increase (decrease) monotonically with temperature, and the relationship between viscosity ν and size of average atomic clusters dS is expressed as a linear function, i.e., ν = ν0 + K·dS, which presents a new way for revealing micro-structure change of alloy melt and further understanding the change characteristic of viscosity.


Study of crystalline structure change of annealing-induced self-organization in polymer field-effect transistors
Yao Jiang-Feng, Jia Quan-Jie, Chen Yu, Tian Xue-Yan, Zhao Su-Ling, Xu Zheng, Zhang Fu-Jun, Gong Wei, Fan Xing
2011, 60 (5): 057201. doi: 10.7498/aps.60.057201
Abstract +
With the aim of understanding the relationships between polymer self-organization and charge carrier mobility of polymer organic field-effect transistor (OFET), we investigate crystalline microstructure change of annealing-induced self-organization of regioregular poly(3-hexylthiophene) (RR-P3HT) active thin layer in polymer OFET by synchrotron radiation grazing incident X-ray diffraction (GIXRD). The crystalline microstructures of RR-P3HT thin film with different preparation methods (spin-coating and drop-casting) and different concentrations (2.5 mg/ml and 3.5 mg/ml) at various annealing temperatures are studied. These results present that, the crystalline structures of RR-P3HT active layers annealed at 150 ℃ are better and enhanced to charge transport, which tend to pack form the thiophene rings are perpendicular and the π-π interchain stacking parallel to the substrate. Furthermore, we find that an appropriate annealing temperature can facilitate the crystal structure of edge-on form, resulting in field-effect mobility enhancement of polymer OFET.
Several auxiliary equations and infinite sequence exactsolutions to nonlinear evolution equations
2011, 60 (5): 050201. doi: 10.7498/aps.60.050201
Abstract +
To seek infinite sequence exact solutions of nonlinear evolution equations, the Böcklund transformation of the solutions to some auxiliary equations and the formula of nonlinear superimposition of solutions are presented for constructing infinite sequence exact solutions to nonlinear evolution equations, which include infinite sequence Jacobi elliptic function solutions, infinite sequence hyperbolic function solutions and infinite sequence trigonomical function solutions. The method is of significance to the search into infinite sequence exact solutions of other nonlinear evolution equations.
An integral of a generalized Birkhoff system
Zhang Yi, Ge Wei-Kuan
2011, 60 (5): 050202. doi: 10.7498/aps.60.050202
Abstract +
The generalized Birkhoff equations are obtained by using supplementary terms added to the Birkhoff equations. An integral of the Birkhoff equations can be used to the generalized Birkhoff equations.An example is given to illustrate the application of the result.
Model solution of perturbed delays in classical physics
Wang Na, Ni Ming-Kang
2011, 60 (5): 050203. doi: 10.7498/aps.60.050203
Abstract +
Using the boundary layer corrective method, one type of perturbed model with delays in classical physics is studied. The asymptotic solution for the model is constructed. The asymptotic behaviors of the solution are also discussed.
Travelling wave solution of the weakly nonlinear evolution equation with control term
Mo Jia-Qi, Ge Hong-Xia, Cheng Rong-Jun
2011, 60 (5): 050204. doi: 10.7498/aps.60.050204
Abstract +
A weakly nonlinear evolution equation with control term is considered using the analytic method. From the perturbation theory, the solution of the corresponding equation is obtained. And the functions of asymptotic solution for the equation are studied.
Soliton solution for the disturbed mKdV coupled system
Xu Yong-Hong, Mo Jia-Qi, Wen Zhao-Hui
2011, 60 (5): 050205. doi: 10.7498/aps.60.050205
Abstract +
The approximate solution for a class of disturbed mKdV coupled system is considered using a simple and valid technique. We first solve the approximate solution of the soliton for a corresponding complex-valued differential equation using the homotopic mapping method. And then the approximate solution of the soliton for a original disturbed mKdV coupled system is obtained.
A sine-Gordon soliton star model with the action of exotic matter and dark energy
Li Ji-Gen, Yan Jun, Zou Bo-Xia, Su Wen-Jie
2011, 60 (5): 050301. doi: 10.7498/aps.60.050301
Abstract +
A sine-Gordon soliton star model with the action of exotic matter and dark energy is studied in this article, the solutions of state equation and mass of star are calculated by using field equation. We found that the density and pressure of matter are connected with the soliton state and the mass of star. Moreover, star equilibrium and stability of dark energy are analyzed and discussed, the result shown that the state of soliton star interior exist in the form of mixed state.
Multiple quadrate soliton solutions and chaotic behaviours of (2+1)-dimensional breaking soliton equation
Lei Jun, Ma Song-Hua, Fang Jian-Ping
2011, 60 (5): 050302. doi: 10.7498/aps.60.050302
Abstract +
With the projective equation method and the variable separation method, new exact solutions of the (2+1)-dimensional breaking soliton equation is derived. Based on the derived solitary wave excitation, we obtain multi-quadrate soliton structures with Weierstrassp function and study the chaotic behaviours of the equation for two chaotic systems.
Study of isotope effect in20Ne(34Ne)-18Na2(23Na2,37Na2) low-temperature collisions
Zang Hua-Ping, Li Wen-Feng, Cheng Xin-Lu, Yang Xiang-Dong, Linghu Rong-Feng
2011, 60 (5): 050303. doi: 10.7498/aps.60.050303
Abstract +
Multiple ellipsoid model is applied to the20Ne,34Ne-18Na2,23Na2 and37Na2collision systems. The integral cross-sections for rotational excitation and total collision cross-sections at the incident energy of 190 meV are calculated. Moreover, at the related incident energy, the contributions of different regions of the potential to the integral cross-sections of rotational excitation for20Ne-18Na2,23Na2 and37Na2 collision systems are investigated. By analyzing the differences of these integral cross-sections, the change rules of the integral cross sections with the change of rotational angular quantum number of Na2 molecule, as well as with the change of the reduced mass of symmetric isotopic substituted system are obtained.
Strengthened quantum Hamming bound
Xing Li-Juan, Li Zhuo, Zhang Wu-Jun
2011, 60 (5): 050304. doi: 10.7498/aps.60.050304
Abstract +
By studying sets of operators with constant weight we present for the first time an analytical upper bound on the pure quantum stabilizer codes whose underlying quantum system can be of arbitrary dimension, which outperforms the so far well-known quantum Hamming bound, the optimal analytical upper bound for small code length.
The research of information dissemination model on online social network
Zhang Yan-Chao, Liu Yun, Zhang Hai-Feng, Cheng Hui, Xiong Fei
2011, 60 (5): 050501. doi: 10.7498/aps.60.050501
Abstract +
In this paper, we propose a general stochastic model for the information dissemination on the online social network. The model considers the node of degree and propagation mechanism, utilizes complex network theory and dynamics of infectious diseases, and finally establishes the dynamic evolution equations. The dynamic evolution equations describe the evolution process of different types of nodes, and show that the propagation process is influenced by network topology and propagation mechanism. We simulate the information spreading process, and analyze the behavior of different types of nodes on online social network. Simulation results show that information can spread easily on the online social network because of the good connectivity. The greater the degree of the initial spread node, the faster the information spreads on online social network. Center nodes have great social influence, and the nodes with different degrees have the similar trend on online social network. Research shows that the model, having the same characteristics with online social network, contributes to a more profound understanding of information dissemination behavior on online social network.
Effects of time delay on transition rate of state in an increasing process of Logistic system
Yang Lin-Jing
2011, 60 (5): 050502. doi: 10.7498/aps.60.050502
Abstract +
The effects of time delay on transition rate from metastable state to stable state in a Logistic system are investigated. On the assumption that there is a delay time in the decay process of cell evolution, the expression of the transition rate is derived in the first order approximation under the condition of the small delay time and the steepest-descent approximation. The numerically calculated results indicate that the additive noise, the multiplicative noise and the correlations between additive and multiplicative noises enhance the system transition from metastable state to stable state. However, such a transition is restrained by the time delay, i.e., the time delay enhances the stability of the system.
Chaos in a neuron model with adaptive feedback synapse: Electronic circuit design
Li Chun-Guang, Chen Jun
2011, 60 (5): 050503. doi: 10.7498/aps.60.050503
Abstract +
In a neuron model with adaptive feedback synapse, with the change of parameters, the existence of two coexisting chaotic attractors, switching from the coexisting chaotic attractors to a connected chaotic attractor,and then switching back to the two coexisting chaotic attractors in this model were recently reported. An electronic circuit design for this model is described in detail in this paper. The circuit design of the non-monotonous activation function unit is also considered in detail. The designed circuits are simulated using the Electronic Workbench (EWB) software. Simulation results demonstrate that the dynamical behaviors of the designed circuit are closely similar to those in numerical simulations.
Hopf bifurcation control of the Rössler system based on Washout filter controller
Wu Zhi-Qiang, Sun Li-Ming
2011, 60 (5): 050504. doi: 10.7498/aps.60.050504
Abstract +
The Washout filter is adopted to control Hopf bifurcation in Rössler system. The effect of its parameters on the position of bifurcation point, the bifurcation type, and the amplitude of periodic solution is discussed in detail. Based on Routh criterion, the stability region in parameter space is found out firstly. Then the influence of the filter’s time constant and the linear gain on the location of bifurcation point is analyzed. By using the Direct Normal Form method, the normal form of the controlled Rössler system is deduced and the coefficient of resonant term is expressed as a function of the nonlinear gain. It is revealed that, by changing the sign and the absolute value of the real part of the coefficient, the nonlinear gain can modify the periodic solution’s amplitude and Hopf bifurcation type. All the results obtained are verified by numerical simulation.
Sliding mode control of chaotic vibrations of spinning disks with uncertain parameter under bounded disturbance
Shen Tao, Ma Xiao-Yi, Chen Di-Yi
2011, 60 (5): 050505. doi: 10.7498/aps.60.050505
Abstract +
In order to eliminate lateral oscillation of spinning disk with uncertain parameter and dispel their adverse effect on the system performance or the working conditions of the system, supposing that the point force acting on the spinning disk is uncertain and bounded, the chaotic complex dynamic characteristics of the four-dimensional nonlinear equations in lateral oscillations of spinning disk under bounded disturbance were analyzed in view of the ubiquity of disturbance, including the space trajectory, the Lyapunov exponent and the Poincaré map. These characteristics enable us to know them deeply, and indicate that the four-dimensional dynamical system contains chaotic attractor. To ensure the robustness of the system control, the author stabilized the chaotic orbits to arbitrary chosen fixed points and periodic orbits by means of sliding mode method, and MATLAB simulations were presented to confirm the validity of the controller. The results show that using sliding mode method can make the system track target orbit strictly and smoothly with short transition time, and its insensitivity to noise disturbance is shown. It provides reference for relevant chaos control in mechanical system.
A fast algorithm for multivariable generalized predictive control of Rössler hyperchaotic system
Chen Zhi-Wang, Liu Wen-Long
2011, 60 (5): 050506. doi: 10.7498/aps.60.050506
Abstract +
A kind of fast multivariable generalized predictive control algorithm for Rössler hyperchaotic system is proposed. The chaotic system with improved recursive least squares parameter of time-varying forget factor is identified, then the output signals of the system follow fast the reference ones for the application of the feedforward gain matrix and softing coefficient matrix in regular performance index function of multivariable generalized predictive control. Moreover, the reduction of inverse matrix dimensions leads to smaller amount of computation of the algorithm. The simulation results show the effectiveness and practicability of this algorithm.
Tracking control and parameters identification of a class of chaotic systems with unknown parameters
Li Nong, Liu Yu, Li Jian-Fen
2011, 60 (5): 050507. doi: 10.7498/aps.60.050507
Abstract +
A tracking control method is proposed for a class of chaotic systems with unknown parameters. The controller and recognizing rules of unknown parameters are designed based on Lyapunov stability theory. The method is illustrated by applications to unified chaotic systems and the simulation results showed the effectiveness of the proposed scheme.
Generalized projective synchronization of chaotic systems via modified active control
Li Zhen-Bo, Zhao Xiao-Shan, Wang Jing
2011, 60 (5): 050508. doi: 10.7498/aps.60.050508
Abstract +
Based on Lyapunov stability theory, by introducing a special matrix structure, a modified active control is proposed for the generalized projective synchronization of chaotic system. Compared with the traditional active control, the modified active control is independent of the Routh-Hurwitz criterion, which means the complexity of active control is simplified. The method is successfully applied to the energy resource system and nuclear spin generator system. Compared with other method, the proposed method, which could realize the generalized projective synchronization between both identical systems and different systems, is shown to be simple, direct, stable and efficient. Numerical simulation is provided to show the validity of the theoretical analysis and the effectiveness of the method.
Optoelectronic or all-optical logic gates using chaotic semiconductor lasers using mutual coupling-feedback
Yan Sen-Lin
2011, 60 (5): 050509. doi: 10.7498/aps.60.050509
Abstract +
We present theoretically the construction of the fundamental gates using two injection semiconductor laser diodes by muans of mutual coupling-feedback. Two laser diodes driven by a common monochromatic light beam run chaos while chaotic synchronization between the two lasers is achieved by coupling-feedback. The optoelectronic logic gate is implemented by appropriately synchronizing or de-synchronizing the two chaotic states by modulating the currents. The all-optical logic gate is finally implemented by appropriately synchronizing or de-synchronizing the two chaotic states via the modulators modulating the coupling lights, which is an external optical modulation method. Numerical results validated the feasibility of the method.
Adaptive synchronization of fractional-order chaotic system via sliding mode control
Zhang Ruo-Xun, Cao He-Fei
2011, 60 (5): 050510. doi: 10.7498/aps.60.050510
Abstract +
Based on sliding mode control theory and adaptive control theory, this paper investigates the synchronization of three-dimensional chaotic systems, designs a fractional order proportional integral switching surface, and proposes a single adaptive-feedback controller for fractional-order chaos synchronization. Simulation results for fractional-order unified chaotic system and Arneodo chaotic systems are provided to illustrate the effectiveness of the proposed scheme.
Fractional sliding mode surface controller for projective synchronization of fractional hyperchaotic systems
Sun Ning, Zhang Hua-Guang, Wang Zhi-Liang
2011, 60 (5): 050511. doi: 10.7498/aps.60.050511
Abstract +
In this paper, a sliding mode controller with fractional sliding surface is designed for projective synchronization (PS) of fractional hyperchaotic systems via active control theory and sliding mode theory. The existence and the stability of PS between two fractional hyperchaotic systems are studied based on Lyapunov theory, fractional stability theory and the theory of fractional calculus. The criterions for the practical stability of the PS error system are presented also. Numerical simulation of PS between fractional Chen system and a new hyperchaotic system shows the effectiveness of the proposed controller law.
The analysis of traffic congestion and dynamic propagation properties based on complex network
Lin Yong, Fu Bai-Bai, Gao Zi-You, Li Shu-Bin, Wu Jian-Jun
2011, 60 (5): 050701. doi: 10.7498/aps.60.050701
Abstract +
The complexity science, as a new crossing discipline, have infiltrated many areas of traffic study. In recent years, studing the problem of urban traffic system with complex network theory offers a new perspective to investigate the generation and propagation of traffic congestion. This paper studies the impact of the network topology on traffic congestion by the improved mesoscopic traffic flow model, and analyzes properties of the occurrence of traffic congestion, which can raise the effective elimination of traffic congestion control strategy as well as make reasonable transportation planning.
High pressure Raman investigation on the Fermi resonance of biphenyl
Zhou Mi, Li Zhan-Long, Lu Guo-Hui, Li Dong-Fei, Sun Cheng-Lin, Gao Shu-Qin, Li Zuo-Wei
2011, 60 (5): 050702. doi: 10.7498/aps.60.050702
Abstract +
Raman spectra of biphenyl have been obtained under pressures up to 15 GPa. The results indicated that with the increase of pressure, the effect of inter- and intra-molecular π-πconjugation and delocation increases, accompanied by the intensity enhancement of the Raman bands, and blue shift of the frequency. The intensity ratio (Rf/a) of two Fermi resonance bands υ'6 + υ' 1 and υ' 8 decreases, and the frequency difference Δ increases with the pressure. The Fermi resonance phenomenon disappears when the pressure goos up to 8 GPa. Using J.F. Bertran's theory, we obtained the relationship of the inherent frequency difference Δ0 and coupling coefficient ω with pressure. This phenomenon was explained by high-pressure phase transition. The mechanism of high pressure induced Fermi resonance weakening was also discussed.
Multiband fractal cross dipole frequency selective surface
Gao Jin-Song, Liang Feng-Chao, Wang Yan-Song, Chen Xin, Wang Shan-Shan
2011, 60 (5): 050703. doi: 10.7498/aps.60.050703
Abstract +
Fractal structures has self-similar properties so that they can be applied in the field of frequency selective surface (FSS) as unit cell and the fractal FSS has the nature of simple ,multi-band characteristics on single layer FSS which can be used as spatial pass filters for the incident angle, polarization and the frequency of the electromagnetic wave. Take fractal cross dipole as example, which we can obtain by recursive algorithm and iterative technique, this work gives the expressions of the fractal elements’ geometry and then characterizes the FSS transmission response by the electric field integral equation for the current distribution on the single FSS screen derived from the Floquet's periodic theory unden impedance boundary condition. Genetic algorithm was applied to globally optimize the structure parameters in order to get the design of the double resonant FSS. Finally, FSS sample was prepared by optical lithography and measured in the anechoic chamber. Experimental results show good agreement with the calculations we made for the design of FSS with resonant frequencies 9.2 GHz and 29.4 GHz, which was what we expected from the periodic method of moment.
Shot noise measurement methods in electronic devices
Zhuang Yi-Qi, Bao Jun-Lin, Chen Wen-Hao, Du Lei, He Liang, Chen Hua, Sun Peng, Wang Ting-Lan
2011, 60 (5): 050704. doi: 10.7498/aps.60.050704
Abstract +
The limitations to shot noise measurement methods based on superconducting quantum interference device (SQUID) and superconductivity-insulation-superconductor (SIS) Josephson junction are pointed out, and a method to measure the shot noises of conventional electronic devices is proposed. Shot noise characteristics of conventional electronic devices are analyzed, and then a low-temperature measurement system is established. By using a double-shielding construction and low noise preamplifier, the test system can achieve a good electromagnetic interference shielding and low background noise. The theoretical and the experimental results of shot noises in diodes at 10 K are in good agreement with each other. The accuracy and the credibility of measurement system are proved.
Simulation and optimization of grating optical coupling of terahertz quantum well photodetector
Zhang Rong, Guo Xu-Guang, Cao Jun-Cheng
2011, 60 (5): 050705. doi: 10.7498/aps.60.050705
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The grating optical coupling method is commonly used for detecting the normal incident light with a quantum well photodetector. In this paper, the distribution of electromagnetic field in one-dimensional metal grating terahertz quantum well photodetectors is studied with modal method, and the average light intensity in the active region is obtained. The result shows that, the light intensity in the device can be optimized when the period of the grating is comparable with the wavelength of the terahertz wave in the sample and a proper filling factor is chosen according to the device structure, which will improve the responsivity of the device.
Beam-wave synchronization and coupling in a multi-gap coupled cavity
Luo Ji-Run, Zhu Min, Guo Wei, Cui Jian
2011, 60 (5): 051101. doi: 10.7498/aps.60.051101
Abstract +
The analytical expressions of the beam-wave coupling coefficients and the beam-loaded conductance in an N-gap coupled cavity are derived based on space-charge wave theory. Through calculating the relations of the beam-wave coupling coefficient and the normalized beam-loaded conductance to the gap number, beam voltage and perveance for 2π mode, the mechanism of the beam-wave synchronization and coupling in the multi-gap coupled cavity are discussed. The results show that, with the increase of N(≥2), the beam-wave coupling efficiency and the normalized beam-loaded conductance vary with beam voltage more rapidly and there is a maximum value for the absolute squared value of the coupling coefficient |MN|2 and a maximum value and a minimum value for the normalized beam-loaded conductance gb. The magnitudes of these extrema increase with the increase of gap number N, and the corresponding voltage is close to the synchronization voltage. The increase of the perveance could make the voltage difference between two extremums of gb increase, the magnitudes of these extrema decrease, and the beam-wave coupling efficiency fall.
Time-domain scattering properties of microstrip array antennas
Wang Jun-Hong, Li Zheng, Zhang Xue-Qin
2011, 60 (5): 051301. doi: 10.7498/aps.60.051301
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In this paper, the scattering characteristics of microstrip antenna arrays in time domain are analyzed using finite-difference time domain (FDTD) method. The distributions of scattering field components, Eθ and Eφ, are studied when the polarization and incidence directions of the incident pulse vary. The relationship of time domain waveforms and spectra of the scattering field with the microstrip antenna array structure is analyzed. The effect of ground plane on the scattering field of microstrip patch array is investigated using the field separating approach. It was found that the scattering field of microstrip antenna array with finite ground plane is mainly generated by the edge current on the ground plane. The resonance frequency of microstrip patch array is associated with the polarization direction of the incident pulse, hence, different polarization directions correspond to different spectra of the scattering field.
The study of shape and shape-coexistence of neutron rich nuclei around N=28
Zhi Qi-Jun
2011, 60 (5): 052101. doi: 10.7498/aps.60.052101
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With the isospin-dependent Nilsson potential, we calculate the properties of the N=28 nuclei in the framework of macroscopic-microscopic model. The shape and shape coexistence of these nuclei are calculated and discusses. It is shown that strong shape coexistences occur in the ground state of nuclei with N=28 in Na, Mg and Al isotopes. It is pointed out that, the ground state of 42Si is oblate shape and there is no obvious shape coexistence for 42Si.
Calculation and analysis of DPA in the main components of CSNS target station
Yu Quan-Zhi, Yin Wen, Liang Tian-Jiao
2011, 60 (5): 052501. doi: 10.7498/aps.60.052501
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The damage energy cross sections and displacement cross sections of W, SS316 and Al-6061, which will be used in the CSNS (China Spalllation Neutron Source) target station, were calculated with the high energy transport code MCNPX 2.5.0. The DPA (Displacement Per Atom) distributions were also calculated and anlyzed for the main components in the CSNS target station, such as the W target, the target vessel, the moderators and reflector vessels. Based on the DPA caused by neutrons and protons, the lifetime of these components were estimated. The influence of the proton beam profile on the peak value of DPA for W target and target vessel were also presented. These calculations and analyses are very important for the under going CSNS project.
Atomic structure calculation model based on plasma fluctuation
Li Xiang-Dong
2011, 60 (5): 053201. doi: 10.7498/aps.60.053201
Abstract +
The new modified Debye-Hückel electron shielding potential, which has been used in the study of fusion cross sections in plasma, is adopted in the atomic structure calculation under plasma environment. By variation of the Tsallis entropic parameter q, the average effect of plasma environment fluctuation is considered in atomic structure of plasma. A calculation using such modified Debye-Hückel potential of the He-like Al shows that the free electron distribution is different between the modified Debye-Hückel model and the linear Debye-Hückel model. This statistic method by considering the plasma fluctuation can also be extended to other plasma screening model, such as the self-consistent ion sphere model.
Theoretical calculation of photonization of F3+ and Ne4+ ions
Sun Chang-Ping, Wang Guo-Li, Zhou Xiao-Xin
2011, 60 (5): 053202. doi: 10.7498/aps.60.053202
Abstract +
We have calculated the partial and total photoionization cross sections for ground states 2s22p2 (3P) and excited states 2s22p2(1D,1S) ,2s2p3 (5So) of F3+ and Ne4+ ions and analyzed and identified the corresponding transitions of autoionization resonances for the ions in the photoionization processes. The obtained resonance structures of total photoionization cross sections are compared with the recent experimental ones and other theoretical calculations. It is shown that our results are in good agreement with the recent experimental ones.
Study of the photodetachment of H- in a microcavity
Tang Tian-Tian, Wang De-Hua, Huang Kai-Yun
2011, 60 (5): 053203. doi: 10.7498/aps.60.053203
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Using the closed orbit theory, we studied the photodetachment cross section of H- in a microcavity, which is made of two parallel metal and elastic surfaces. The results show that both the upper and lower surfaces of the microcavity have great influence on the photodetachment cross section of H-. If we fix the distance between the metal surface and H-, when the distance between the elastic surface and H- is large, the influence of the elastic surface on the photodetachment cross section is small. The oscillation amplitude and the oscillation frequency of the cross section approach to the case of the photodetachment of H- near a metal surface. With the decrease of the distance between the elastic surface and H-, the oscillation amplitude is increased and the oscillation frequency is decreased. If we fix the distance between the elastic surface and H-, with the increase of the distance d0 between the metal surface and H-, the influence of the metal surface is decreased. When the d0 is increased to 500 a.u. the cross section approaches to the case of the photodetachment of H- near an elastic surface. So we can change the distance between the upper and lower surface of the microcavity to control the photodetachment of H-. This study provides a new understanding on the photodetachment process of H- in the presence of surfaces and microcavity.
The radiation pressure and laser cooling of a V-type three level atom
Zhang Qin, Tang Yuan-He, Qu Guang-Hui, Jin Kang
2011, 60 (5): 053204. doi: 10.7498/aps.60.053204
Abstract +
The radiation pressure and laser cooling of a V-type three level atom in coherent fields in a squeezed vacuum are considered. From the Hamiltonian of the atomic system, making use of Born-Markoff approximation, the optical Bloch equations are derived. Using the adiabatic approximation, the expression of the mean dissipative force are acquired. The achievable equilibrium temperature is given by the quantum regression theorem and Einstein relation. The dependence of the spontaneous radiation pressure and ultimate temperature on quantum interference, average photon number and Rabi frequency are analyzed. The result shows that temperatures lower than the Doppler limit can be achieved.
Nonsequential double ionization of argon atom below the recollision threshold
Zhang Dong-Ling, Tang Qing-Bin, Yu Ben-Hai, Chen Dong
2011, 60 (5): 053205. doi: 10.7498/aps.60.053205
Abstract +
Nonsequential double ionization (NSDI) of Ar atom below the recollision threshold is investigated using the three-dimensional classical ensembles. The calculated results reveal a dominance of events for electron emission into opposite hemispheres, a clear minimum of the correlated electron-electron momentum distributions at the origin and a single peak structure of the Ar2+ ions longitudinal momentum spectra near zero momentum. The momentum spectra of the Ar2+ ions agree with the experimental results 101 053001 (2008)] quantitatively. Trajectory back analyses show that the microscopic physical mechanisms of Ar NSDI are distinct for different intensities of the laser. When laser intensity equal to 0.7×1014 W/cm2, one recollision dominates the process of the recollision. However,the domination convert to multiple recollisions as the laser intensity decreases to 0.4×1014 W/cm2. In addition, the Coulomb attraction between the ion and electron plays an important role in microscopic dynamics of the electron in the process of Ar NSDI and eventually influences the final-state correlated electron-electron momentum distributions strongly.
Isolated intense 38 attosecond pulse generation from the combined laser pulse irradiating the coherent superposition state
Chen Ji-Gen, Yu Xu-Ping, He Long-Jun, Xu Yuan-Yuan, Yang Yu-Jun
2011, 60 (5): 053206. doi: 10.7498/aps.60.053206
Abstract +
A scheme to efficiently generate an intense short isolated attosecond pulse is presented by the combined laser pulse irradiating the coherent superposition state. The combined pulse is composed of a multi-cycle 800 nm laser and a 1600 nm one. Compared with the case of the fundamental laser irradiating the ground state, the cutoff position is significantly extended from 70th to 280th harmonic, a broadband supercontinuum spectrum with 108 eV spectral width can be produced which directly generates an isolated 38 attosecond pulse, the intensity of which is increased eleven orders of magnitude. Our simulation also shows that the value of the time delay has a large range to keep the isolated sub-50-as pulse generation. Moreover, the value of the time delay in the range between ±0.05π is optinal. This result shows that the scheme appears feasible for an experimental demonstration.
Theoretical calculation of valence shell ionization potentials of XF3(X=N, P, As) using the equation-of-motion coupled cluster method
Cheng Xin-Lu, Zhou Xue-Ping, Tang Hai-Yan, Chen Heng-Jie
2011, 60 (5): 053301. doi: 10.7498/aps.60.053301
Abstract +
The equation-of-motion coupled cluster method with full inclusion of singles and doubles (EOM-CCSD) is applied to evaluate the vertical ionization potential (VIP) of XF3(X=N,P,As). At the same time, symmetry adapted cluster configuration interaction (SAC-CI), the outer valence shell Green function (OVGF) and partial third order approximation (P3) are also employed. Comparison with results of some experiments show average errors of 0.2 eV in the whole valence shell ionization region and are better than OVGF and P3 values and similar to the SAC-CI values. With the increase of basis set, the difference of the first VIP value between the EOM-CCSD and experimental becomes smaller and the different is about 0.03 eV. According to results from SAC-CI, OVGF, P3 and EOM-CCSD of NF3 and PF3, we can conclude that the first IP of AsF3 is not 12.3 eV but about 12.8 eV, the valence shell ionization potentials are 12.64,15.23,16.30,17.37,18.05 and 21.98 eV.
Emission spectra of OH radical (A2Σ+→X2Πr) and its application on high temperature gas
Yang Qian-Suo, Jiang Zong-Lin, Peng Zhi-Min, Ding Yan-Jun
2011, 60 (5): 053302. doi: 10.7498/aps.60.053302
Abstract +
Based on the inherent molecular structure characteristics of the OH radicals, the energy level distribution, the transition frequency and Einstein spontaneous emission transition probability are systematically analyzed and numerically studied. Meanwhile, combined with the spectra experiments, the natural broadening, collision broadening, Doppler broadening and instrumental broadening effects on spectral line shape are analyzed. The dependence of the spectral profile on the rotational temperature, the vibrational temperature, and the spectral function are numerically explored in certain ranges. The corresponding numerical results are also discussed for the emission spectra thermometry, which provides a theoretical basis for the emission thermometry. In experimental, the emission spectra of OH (A2Σ+→X2Πr) system of the hydrogen flames are recorded by the optical multi-channel analyzer and studied. By the fitting of the experimental spectra to the numerically calculated spectra, the corresponding rotational and vibrational temperatures of the hydrogen flames are determined, respectively.
The quasi-classical trajectory study in the reaction C+OH(v=0—3, j=0—3)→CO+H
Wang Ping
2011, 60 (5): 053401. doi: 10.7498/aps.60.053401
Abstract +
The effect of reagent vibrational and rotational excitation on the stereodynamics in the chemical reaction C+OH at the collision energy of 1.0 eV has been carried out by using the quasi-classical trajectory method. The vector property of different vibrational and rotational states has been discussed in detail. The results suggest that the vibrational and rotational excitation of OH are very sensitive to the vector property of the C+OH reaction, which is different from the study of the scalar property of the C+OH reaction.
Influence of laser pulse on the photodetachment of H- ion near a metal surface
Wang Shan-Shan, Wang De-Hua, Tang Tian-Tian, Huang Kai-Yun
2011, 60 (5): 053402. doi: 10.7498/aps.60.053402
Abstract +
Using the closed orbit theory and the formulas of double-pulse laser pulse photodetachment cross section of H- ion near a metal surface, we calculated the laser pulse photodetachment cross section of this system. The results suggest that for the double-pulse laser, if the pulse width is much longer than the particular closed orbit period, the contribution of that closed orbit to the photodetachment cross section is very small. If the pulse width is shorter or can be compared with the particular closed orbit period,the contribution of that closed orbit to the photodetachment cross section is reduced. The cross section depends not only on the pulse width, but also on the time delay and the relative phase of the two pulses. For certain relative phase between the two pulses, the photodetachment cross section is increased; while for other relative phases, the photodetachment cross section is reduced. Therefore, we can use the pulse laser to control the photodetachment process of H- near a metal surface. We hope our results will be helpful for experimental research of photodetachment of negativeion influenced by pulse laser near surfaces.
Theoretical study of geometry structures and stability of OsnN0,±(n=1—6) clusters
Zhang Xiu-Rong, Wu Li-Qing, Tang Hui-Shuai, Kang Zhang-Li
2011, 60 (5): 053601. doi: 10.7498/aps.60.053601
Abstract +
The possible geometrical and electronic structures of (OsnN)0, ±(n=1—6) clusters are optimized by using the density functional theory (B3LYP) at the LANL2DZ level. For the ground state structures of (OsnN)0,±(n=1—6) clusters, the average binding energies, second finite differences, dissociation energies and energy gaps are analyzed. The calculated results show that there are many different isomerides in (OsnN)0,±(n=1—6) clusters. With the increase of number of atoms, the N atom tend to the peripheral endpoint; the clusters show "odd - even" oscillation and "magic number" effect. The cluster is more stable when the number of atoms is even than odd. It was found that the Os3N+ and Os5N+ clusters are the most stable and n=4 clusters is the least stable, yet the stability of (OsnN)0,±(n=1—6) clusters have increased significantly than pure osmium clusters.
The axial distribution of carbon dioxide cluster in supersonic gas jet by Rayleigh scattering
Fu Peng-Tao, Han Ji-Feng, Mou Yan-Hong, Han Dan, Yang Chao-Wen
2011, 60 (5): 053602. doi: 10.7498/aps.60.053602
Abstract +
The axial distribution of carbon dioxide clusters in supersonic gas jet was studied by Rayleigh Scattering method. It is found that the logarithm of scattering signal ln(S) decreases linearly with the square root of Z and the position of 4 mm rather than the position nearest the nozzle has the maximum average cluster size. The scattering signal intensity exhibits a power scaling on the backing pressure ranging from 6 to 17 bar , and the power varies from 3.6 to 4.2. The axial cluster size was estimated and the maximum size was found to be 16 000 molecules/cluster.
Theoretical and experimental study on transmission properties of THz wave in metal-coated hollow waveguide
Geng You-Fu, Zhou Jun, Tan Xiao-Ling, Yao Jian-Quan
2011, 60 (5): 054101. doi: 10.7498/aps.60.054101
Abstract +
Limited by serious material absorption and dispersion in THz wave band, efficient and long distance delivery of THz signal is one of important problems for constructing a compact THz system. Based on the transmission loss coefficient in metal waveguide obtained by perturbation method, the transmission loss properties of THz wave in metal-coated hollow waveguide varying with different metal materials and waveguide structure parameters are simulated. According to the numerical results, an Ag-coated hollow waveguide with inner diameter of 1.1 mm was designed and fabricated, and the transmission loss of THz wave was 8.6 dB/m at frequency of 2.5 THz as found in experiment, which realizes a short distance transmission with ultralow loss in THz region.
Selectable electromagnetic response modes and negative refraction in rectangular dielectric metamaterials
Zhou Qiang, Hu Wei-Qin, Cai Gen-Wang, Liang Er-Jun, Ding Pei
2011, 60 (5): 054102. doi: 10.7498/aps.60.054102
Abstract +
Dielectric resonator is a kind of important building block for metamaterials. Here, we numerically investigated the resonance modes excited in the dielectric resonator whose cross section has different ratios of the length to width. It is found that the cross-sectional aspect ratio has great influence on the excitation sequence of the resonance modes. The magnetic resonance mode is firstly excited for the aspect ratio smaller than 2.2, whereas it is excited at the second resonance for the ratio lager than 2.2. As the turning point, i. e. with the aspect ratio of 2.2, the magnetic mode cannot be achieved. The calculations also show that the magnetic resonance can be tuned by adjusting the direction of the incident electromagnetic wave, thus achieving the polarization control of electromagnetic response. This study provides valuable information for the design and research of novel dielectric-based metamaterials.
Negative refractive index metamaterials based on high-permittivity substrates and metallic structure: design, simulation and experiment
Yang Yi-Ming, Wang Jia-Fu, Qu Shao-Bo, Xia Song, Wang Jun, Xu Zhuo, Bai Peng, Li Zhe
2011, 60 (5): 054103. doi: 10.7498/aps.60.054103
Abstract +
By printing single-loop mirror-symmetrical split-ring resonators on high-permittivity substrates, a type of negative index material was realized with less usage of metals and broader negative-index bandwidth than conventional negative index materials. The underlying mechanisms of realizing negative permittivity by means of high-permittivity substrates and of double-negative pass-band were analyzed. The influening factors on the double-negative pass-band were analyzed both numerically and experimentally. By experiments, the proposed method of realizing double-negative property was verified. Both the theoretical and experimental results show that broad double-negative pass-band can be realized using the proposed method.
Implementation of two-element antenna array with right/left-handed transmission line metamaterials
Zheng Kui-Song, Wu Chang-Ying, Wan Guo-Bin, Wei Gao
2011, 60 (5): 054104. doi: 10.7498/aps.60.054104
Abstract +
To overcome the limitation that the linear transverse dimension of microstrip antenna is of the order of half wavelength, a two-element antenna array has been proposed with composite right/left-handed transmission line metamaterials in this paper. The antenna array is made of two same antenna elements. Each element consists of three radiating patches, interdigital capacitance between two radiation patches and shorted pin connecting radiating patch with ground plane. Therefore, a composite right/left-handed transmission line metamaterials is constituted by radiating patch, shorted pin, antenna of substrate and ground plane. An arched microstrip line is used to connect two antenna elements. The phase difference between two antenna elements is set by adjusting the length of arched microstrip line. S parameters of antenna array obtained by numerical computation are in good agreement of that obtained by measurement. Meanwhile, zeroth-order resonant frequency of two-element antenna array is consistent with that estimated by the circuit theory with extracting equivalent circuit parameters of composite right/left-handed transmission line metamaterials. The peak gain of this antenna array is 6.3dB. Seen from this point, the antenna peak gain is enhanced. When operating in the zeroth-order resonant frequency, physical dimensions of this antenna element are reduced to 0.28λ0×0.1λ0. Here λ0 is a zeroth-order resonant wavelength. The proposed antenna array is a novel venue for antenna miniaturization.
Sub-wavelength imaging of the two-dimensional photonic crystal with effective index close to -1
Zhuang Song-Lin, Tian Shuang, Tong Yuan-Wei
2011, 60 (5): 054201. doi: 10.7498/aps.60.054201
Abstract +
This paper aims at designing a 2D photonic crystal (PC) with negative refractive index close to -1. Plane wave expansion method (PWEM) is used to obtain the band diagram and its equal-frequency surface (EFS). And the finite difference time domain (FDTD) simulation method is also used to analyze the equivalent refractive index of the PC. The results show the equivalent refractive index of the PC close to -1 within a certain frequency band. A super-lens is formed by this photonic crystal, which can form a non-near-field image. Moreover, the super-lens has the capability of sub-wavelength imaging with its effective index close to -1.
Orientation-enhanced and holographic storage of a novel azobenzene doped polymer
Zhao You-Yuan, Xie Ru-Sheng
2011, 60 (5): 054202. doi: 10.7498/aps.60.054202
Abstract +
A novel optical high-density storage material ADPA-PVK-PBA-TNF polymer film was reported. In the nonresonant absorption of sample, we tested and investigated its photo-induced birefringence and obtained the value Δn =1.3×10-3.We analyzed the physico-chemiscal mechanism of orientation-enhancement and discussed the enhancing/restraining effects of photo-induced birefringence in the film. On this basis,multiple angles storage were achieved and clear holographic storage images were gained. The enhancing/restraining effect of image storage was also discussed. And with the help of this effect one can process and remove storage images.
Fabrication of triangular chirped fiber Bragg grating and its application in single-sideband modulation based radio over fiber system
Li Jing, Ning Ti-Gang, Pei Li, Zhou Qian, Hu Xu-Dong, Qi Chun-Hui, Gao Song, Yang Long
2011, 60 (5): 054203. doi: 10.7498/aps.60.054203
Abstract +
In this work, we present an approach for fabricating triangular chirped fiber Bragg grating. Application of single-sideband modulation based radio over fiber system employing this grating is also analyzed. The proposed technology is based on phase mask and index modulation with changing velocity. A triangular fiber Bragg grating with 1.9 nm base width of transmission spectrum and 0—15 dB of transmission depth was fabricated experimentally. Due to the negative slope in transmission spectrum, the grating can be used in the radio over fiber system. In the proposed scheme, only a single grating is used to achieve two functions, i.e. OSSB+C generation from DSB modulation signals, and reducing the carrier to sideband ratio of the generated signals. Numerical calculation and simulation ware performed and some discussions are given.
The propagation properties of broadband pulse
Li Qin, Guo Hong
2011, 60 (5): 054204. doi: 10.7498/aps.60.054204
Abstract +
The propagation of broadband pulse in a medium with electromagnetically induced transparency (EIT) was studied. The results show that if the carrier frequency of pulse is exactly tuned to the center of the transparency window, and the pulse spectrum is broader than transparency window, the pulse is temporally broadened and the delay effect is significant. If the carrier frequency of pulse the is exactly tuned to the region of absorption, and the pulse spectrum is wide with respect to the width of absorption line, the pulse begins to distort after a certain distance and is split into two parts at last. The peak value depends not only on the frequency and intensity of the coupling field, but also on the length of the sample. Under appropriate conditions, strong and time domain narrowed pulse can be obtained in the output light.
The study on the produced length of whispering-gallery-mode fiber laser
Zhu Kun, Zhou Li, You Hong-Hai, Jiang Nan, Pu Xiao-Yun
2011, 60 (5): 054205. doi: 10.7498/aps.60.054205
Abstract +
Long length of whispering-gallery-mode fiber lasing emission along a fiber's axis is obtained by using the method of evanescence-wave optically pumped and gain coupled fiber laser. The relationship between produced length of lasing emission and pumping energy has been investigated. With the increasing of pumping energy, it is found from our experiment that the length of whispering-gallery-mode lasing emission along the fiber's axis is increased sharply, when the pumping energy is just larger than the threshold energy. However, the increasing trend of the produced length is slow when the pumping energy is much larger than the threshold energy. It was also found from the experiment that both dye concentration and refractive index of cladding gain solution have key affects on the produced length. Based on the characteristic of frustrated totally internal reflection of light traveling along the fiber, and the theory of evanescence-wave pumped and gain coupled fiber laser, an equation determining the produced length of lasing emission has been deduced, the calculated result with the equation matches the experimental data very well.
Carrier-envelope stabilized few-cycle infrared laser system
Song Li-Wei, Li Chuang, Wang Ding, Xu Can-Hua, Leng Yu-Xin, Li Ru-Xin
2011, 60 (5): 054206. doi: 10.7498/aps.60.054206
Abstract +
According to the feature of the passive carrier-envelope phase (CEP) stabilized idler of the optical parametric amplified process, a CEP stabilized three-stage collinear optical parametric amplifier is built. Millijoule ultrashort infrared output (1.4 mJ/40 fs/1 kHz at 1.8 μm) with CEP fluctuation ~516mrad is obtained from the system. After passing through a hollow-core fiber and block material, the pulses are finally compressed to less than two cycles (<12 fs), and the single pulse energy is 0.54mJ. The system provides an excellent laser source for the experiments of individual attosecond pulse generation and other high harmonic generation (HHG).
Influences of effective gain length and attenuation coefficient on output energy of stimulated Brillouin scattering in water
He Xing-Dao, Xia Jian, Shi Jiu-Lin, Liu Juan, Li Shu-Jing, Liu Jian-An, Fang Wei
2011, 60 (5): 054207. doi: 10.7498/aps.60.054207
Abstract +
In this paper, the effects of attenuation coefficient and effective gain length on output energy of stimulated Brillouin scattering (SBS) in water are investigated theoretically and experimentally. The experimental results indicate that the smaller the attenuation coefficient, the higher the output energy of SBS is. When the energy of incident laser is very high and the effective gain length is long enough, the SBS may obtain high enough energy thereby reach an extremely strong peak power due to the pulse compression; once it exceeds the threshold of SRS or second-order SBS, the SBS is able to excite an SRS or a second-order SBS as a new source and consumes a part of its own energy. Therefore, the longer the effective gain length, the lower the output energy of SBS is.
Study on measuring the kinematic viscosity of liquid medium based on the energy reflectivity of SBS
Geng Xi-Zhao, Hasi Wu-Li, Guo Xiang-Yu, Li Xing, Lin Dian-Yang, He Wei-Ming, Fan Rui-Qing, Lü Zhi-Wei
2011, 60 (5): 054208. doi: 10.7498/aps.60.054208
Abstract +
In the paper, a method of measuring the kinematic visicosity of liquid medium based on stimulated Brillouin scattering (SBS) at different temperatures is proposed. The kinematic visicosity of liquid medium, which is related to the temperature, greatly affects the gain coefficient of medium and SBS characteristics. Therefore the kinematic visicosity at different temperatures can be measued by the reflectivity of SBS. In experiment, the kinematic visicosities of water at different temperatures are determined based on SBS in continuum's Nd:YAG seed-injected laser and compared with the results measured from kinematic viscosimeter, and the relative error of the experiment results is less than 5%.
General formulation of nonlinear Thomson scattering of arbitrary polarized laser and optimal conditions for X-ray production
Zhao Shi-Hua, Lü Qing-Zheng, Yuan Su-Ying, Li Ying-Jun
2011, 60 (5): 054209. doi: 10.7498/aps.60.054209
Abstract +
The general formulation of nonlinear Thomson scattering of arbitrary polarized laser is derived from electrodynamics analytically under relativistic conditions. The extreme condition for high order harmonics is educed from the analytical results. It is found that the circular polarization reaches a maximum while the linear polarization is at its minimum in the fundamental backscattering radiation in the same situations, which makes important consulting sense in the experimental research of X-ray source based on the Thomson scattering mechanism especially for high intensity incident laser pulse cases.
The relationship between conversion efficiency of high-order harmonic generation from atom and wavelength in two-color combined fields
Cheng Chun-Zhi, Zhou Xiao-Xin, Cao Wei-Jun
2011, 60 (5): 054210. doi: 10.7498/aps.60.054210
Abstract +
By solving the time-dependent Schrödinger equation under velocity gauge with split-operator method, we studied the high harmonics of one-dimensional helium atom exposed to one-color laser field and two-color fields composed of IR field and UV field. And the relationship between conversion efficiency of high-order harmonic generation near the cut-off position and wavelength of the laser (800—2000 nm) was also analyzed. It was found that high-order harmonic conversion efficiency driven by two-color laser field near the cut-off position changes with wavelength as η(λ)∝λ-x,where the x value depends on the intensity of laser field, and the appropriate selection of intensity of combined laser field can improve high harmonic conversion efficiency near the cut-off position.
Visible light metamaterials based on the double-fishnet structure
Zhao Yan, Xiang Jian-Kai, Li Sa, Zhao Xiao-Peng
2011, 60 (5): 054211. doi: 10.7498/aps.60.054211
Abstract +
A novel method was proposed to fabricate double-fishnet structure metamaterials working at visible frequencies. Via template-assisted electrochemical deposition, silver nanonets with different lattices were fabricated, which were used to achieve final double-fishnet structures. It was revealed that the passband of the silver nanonet structure was shift to shorter wavelength when changing the lattice of structure smaller, according to the transmission spectra. Silver nanonet with lattice of 420 nm was used to achieve double-fishnet structure, which has novel effects at 610 nm wavelength, such as enhanced transmission and planar focusing. Furthermore, it is possible to fabricate double-fishnet structure metamaterials working at shorter wavelengths even for blue light when using template with smaller lattice.
Investigation on the fabrication and luminescence characteristics of Yb3+ and Al3+ Co-doped silicate glasses
Han Ying, Xia Chang-Ming, Hou Lan-Tian, Zhou Gui-Yao, Hou Zhi-Yun
2011, 60 (5): 054212. doi: 10.7498/aps.60.054212
Abstract +
We demonstrate a new method for fabrication of rare-doped silica-based glass, which is liquid doped with non-chemical vapor deposition (non-CVD) melting process. The Ytterbium doped silica-based glass with the ratio of 98SiO2-0.5Yb2O3-1.5Al2O3wt% is achieved by using this method. The refractive index (nD) and the density(ρ) of the glass are 1.519 and 2.62g/cm3 respectively. In measurement experiment, it shows that it has strong absorption in the wavelength range from 850nm to 1050nm, and the main absorption peak is at 978nm and the secondary absorption peak is at 919nm. Using the laser with wavelength of 978nm as pumping source, the emission peak is at 1018nm in the fluorescence spectrum with a 71.8nm fluorescence half-line width. Meanwhile, the integrated absorption cross section, stimulated emission cross section, fluorescence time, saturated pump intensity, minimum pump intensity and other parameters are calculated. Test results indicate that the doped silica-based glass has good thermal stability and large power threshold, which is an ideal gain medium for large power photonic crystal fiber lasers.
Parametric analytical model for off-axis illumination sources based on Sigmoid function
Liu Wei, Wu Xiao-Fei, Zhang Chuan-Wei, Liu Shi-Yuan
2011, 60 (5): 054213. doi: 10.7498/aps.60.054213
Abstract +
This paper proposes a parametric analytical source model for overall representation of the physical distribution property of off-axis illumination sources in lithographic tools. A Sigmoid function is adopted as a kernel function to construct the analytical model for the multiple mainstream off-axis sources. Corrected parametrical terms are subsequently presented for characterization of different physical distortions and deviations of real illumination sources. The corrected parametrical terms can be decomposed into Fourier series which have the special physical meaning of respectively indicating different distortion types including shift of the center, tilt, ellipticity, etc. The proposed analytical model provides both simulation condition and theoretical basis for the resolution enhancement technique and the related research fields, thus has important applications.
Study on a novel optical filter by internal reflection and optical rotation
Zhang Bin, Pan Xue-Feng, Tao Wei-Dong
2011, 60 (5): 054214. doi: 10.7498/aps.60.054214
Abstract +
Based on the optical rotatory dispersion and the isotropy of the sodium chlorate crystal, a new type of optical filter by internal reflection and optical rotation is firstly developed. Due to the speciality of the zero reflectivity when the linearly polarized light is reflected at Brewster angle, the optical filter can give a good filtering effect by using only a single polarizer. The filtering characteristics were analyzed by Mueller matrix and tested by experiment. The results show that the intensity of emitted red or green light can be continuously modulated by changing the angle of the polarizer. The extinction of green or red light appears when the rotation angle of the polarizer is respectively 133.36° or 173.06° relative to the initial position. The isolation of green and red can be about 10 dB.
The research of the air-sensitive sensor based on thephotonic crystal beam splitter
Kong Yan-Mei, Gao Chao-Qun, Jing Yu-Peng, Chen Da-Peng
2011, 60 (5): 054215. doi: 10.7498/aps.60.054215
Abstract +
The spectroscopy is the ultimate way for chemical analysis. This paper mainly describes the idea of an air-sensitive sensor based on MEMS technology, and more over, a photonic crystal (PC) beam splitter was designed, which can achieve high resolution beam steering, and this improves the resolution of the sensor. The paper offers a new idea and lays the foundation for the novel beam splitter that applied to many optical systems.
Ultrasonic frequency coordination relation of the acousto-optic tunable filter
Li Shi-Jun, Ren Yu, Lu Jun, Cai Hong-Xing
2011, 60 (5): 054216. doi: 10.7498/aps.60.054216
Abstract +
In this paper, the ultrasonic frequency coordination relation has been re-designed in the high-dimensional space by the principle of Kernel function nonlinear mapping. The relative deviation of ultrasonic frequency coordination relation from the original formula has been obtained by analyzing I.C.Chang theoretical model and P.A.Gass revised theoretical model concretely, theraby indicating the inadequacy of the two theoretical models; Using the principle of the nonlinear mapping to map the original data samples into a high dimensional kernel space, in other words, translating the nonlinear problem into a linear problem can clarify the relationships not only between ultrasonic frequency and incident angle but also between ultrasonic frequency and optical wavelength, leading to an appropriate kernel function and the improved coordination of the ultrasonic frequency relation.
Study on dispersion compensation property of octagonal photonic crystal fibers
Zhang Li-Chao, Hou Lan-Tian, Zhou Gui-Yao
2011, 60 (5): 054217. doi: 10.7498/aps.60.054217
Abstract +
The dispersion compensation property of octagonal photonic crystal fibers (PCFs) was simulated with multipole method in this paper.It was found that the dispersion, dispersion slope and Kappa parameter of PCFs can be designed precisely but changing the air hole size and the pitch in PCFs cladding.We compared photonic crystal fiber of hexagonal structure with that of octagonal structure, both of which have the same structure parameters. It was found that the octagonal structure easily abtains large negative dispersion and low non-linear coefficient. It was demonstrated that the octagonal structure has huge potential in designing diepersion compensation PCFs. So, we designed a novel PCF with octagonal structure.The PCF achieves a negative dispersion of -1434.9 ps·nm-1·km-1 and a negative dispersion slope of -4.6338 ps·nm-2·km-1 at λ=1.55 μm, which is far better than the conventional fibre.
Analysis of theoretical model of thermal infrared imager based on the substrate-free focal plane array
Jiang Xing-Kai, Zhang Qing-Chuan, Shi Hai-Tao, Mao Liang, Cheng Teng, Wu Xiao-Ping
2011, 60 (5): 054401. doi: 10.7498/aps.60.054401
Abstract +
Based on thermal deformation of bi-material microcantilever, the focal plane array (FPA)of uncooled optical readout infrared(IR) imaging system has undergone a development from substrate array to substrate-free array. The experimental imaging result and finite element method (FEM) analysis indicated that the substrate-free focal plane array (FPA) did not accord with the condition of constant frame temperature. This paper proposed a new theoretical model on thermal transmission of substrate-free FPA with electrical analogy method. Considering the system as a whole, the analysis of complex thermal interaction of adjacent elements could be averted while the heat absorption and transmission of frame could be considered. The temperature of outer frame was set to be equal to the ambient temperature as a boundary condition. Although it was not so flexible compared with FEM analysis when dealing with the boundary condition, the theoretical model was proved to correspond with the experimental result, and could be used as an approximate formula in thermal response calculation of substrate-free FPA. The model avoids the complication of FEM analysis, especially for large arrays. Further more, the model can be used for substrate-free FPA dimensions design and optimization under certain response target.
Maximum ceasing angle of inclination and flux formula for granular orifice flow
Peng Zheng, Jiang Yi-Min
2011, 60 (5): 054501. doi: 10.7498/aps.60.054501
Abstract +
This work measured mass flux of a granular sample (glass beads) discharged from an inclined orifice for various inclination angles and orifice diameters. It is found that irrespective the orifice sizes, the fluxes all vary linearly with cosine of the inclination angle,and the linearly extrapolated angle of zero-flux,namely the critical angle of flow ceasing, increases linearly with ratio between grain and orifice diameter, tends to the angle of repose in the limit of infinite orifice diameter within an approximation of the Bagnold angle. The results show that the flux formula varying linearly with cosine of inclination angle is capable to reveal behaviors of the critical ceasing angle, a property that the Beverloo formula of which parameters vary with cosine of inclination angle can not describe.
The deformation process of viscous liquid drop studied by using kernel gradient corrected SPH method
Jiang Tao, Ouyang Jie, Zhao Xiao-Kai, Ren Jin-Lian
2011, 60 (5): 054701. doi: 10.7498/aps.60.054701
Abstract +
In this paper, a kernel gradient corrected smoothed particle hydrodynamics (KGC-SPH) method is proposed to simulate the deformation process of a viscous liquid drop. The KGC-SPH method has higher accuracy and better stability than the SPH method, which is verified by simulating the stretching and rotating process of an isothermal viscous liquid drop, and the property of preservation of total angular momentum of the present method is also checked. And then, the formation of a stable spherical liquid drop based on van der Waals model is investigated, and a phenomenon of periodic oscillation with small amplitude is observed. Meanwhile, a new variable smoothing length is presented to remove the unstable phenomenon and a new surface tension technique is adopted in the simulation. Subsequently, the phenomenon of periodic oscillation of a van der Waals model liquid drop is simulated using KGC-SPH method, in which the influence of the elongation and Reynolds number on the amplitude and oscillation period is discussed.
Numerical simulation of bubbles coupled with an elastic membrane
Wang Shi-Ping, Zhang A-Man, Liu Yun-Long, Yao Xiong-Liang
2011, 60 (5): 054702. doi: 10.7498/aps.60.054702
Abstract +
Based on the previous studies, the numerical model of oscillating bubble coupling with elastic membrane is built under the consideration of buoyancy, surface tension and different fluid density ratios. Provided that the fluid around bubble is incompressible the boundary element method is adopted to solve this model and the numerical results coincide well with the Turangan’s experimental results. Through the numerical simulation of the oscillating bubble near elastic membrane, the characteristics of bubble are discussed in fluids of the same density or different densityies separated by the elastic membrane, together with the jet features under the combination of elastic membrane and buoyancy. All these work is to present references to the research on dynamic behavior of bubble near elastic membrane.
Study on attenuation characteristics of millimeterwave in plasma
Luo Xian-Gang, Ma Chun-Guang, Zhao Qing, He Guo, Zheng Ling, Liu Jian-Wei
2011, 60 (5): 055201. doi: 10.7498/aps.60.055201
Abstract +
In order to study the interaction between millimeter wave and plasma, by using time-domain integration method to simulate the attenuation characteristics of millimeter wave propagation in the plasma ,this paper makes preliminary study on the relationships betwcen the attenuation value of millimeter waves propagation in the plasma, plasma density, the collision frequency and operation frequency. By comparing and analyzing the theoretical results with simulation results, the feasibility of the fact that simulation can be used to provide data support for the theoretical study is verified.
Transport properties of titanium and silver plasmas in the region of partial ionization
Chen Qi-Feng, Chen Xiang-Rong, Fu Zhi-Jian
2011, 60 (5): 055202. doi: 10.7498/aps.60.055202
Abstract +
The composition of metal plasmas provides the fundamental parameters for the thermodynamic, optical, and transport properties research. In this paper, the composition of the plasmas, considering the threefold ionization of metal, the polarization between neutral particles and electron, and the Coulomb interactions among the charge particles, (including ion-ion, electron-ion, and electron-electron interactions), is calculated by partially ionized plasma model. Furthermore, the electrical conductivities of titanium and silver are calculated by using linear response theory. The reliability of the model is verified by comparing with available experimental data. Furthermore, the thermal conductivities and thermopower of titanium and silver in the range of 0.001—2.0 g/cm3, 1.5×104—2.5×104 K are predicted, which provides the reference for the experiment of transport properties of metal plasmas.
Transverse dispersion laws in ultra-relativistic plasma with fast electron distribution
Liu San-Qiu, Guo Hong-Mei
2011, 60 (5): 055203. doi: 10.7498/aps.60.055203
Abstract +
Analytic and numerical study of electromagnetic oscillations of isotropic relativistic plasma with fast electron distribution is presented. Different analytic formulas for the long-wavelength and short-wavelength branches are obtained. The numerical study gives the dispersion curve in the whole wavenumber range. It is shown that analytical dispersion curves in the long-wavelength and short-wavelength regions are coincident with the numerical ones. Furthermore, the approximate expression of the dispersion law for the different parameters is given by fitting numerical curves with the polynomial regression method, which provides a reference for further study.
Slow-wave electromagnetic instability driven by wiggling relativistic electron beam in ion-channel
Wang Zhen-Yu, Tang Chang-Jian
2011, 60 (5): 055204. doi: 10.7498/aps.60.055204
Abstract +
The slow-wave electromagnetic (EM) instability excited by a relativistic electron beam (REB) injecting plasmas has been studied using linear electromagnetic hydrodynamic (EMHD) theory. The features of multiple waves propagation are presented. The results of numerical calculation prove that the EM instability occurs in slow-wave band. The necessary and sufficient condition of the EM instability has been found. Both analytic discussion and physical analysis reveal that the electron betatron motion is one of important factors for the EM instability. The physical mechanism of the instability driven by the electron betatron motion has been discussed.
Research of implosion dynamics for wire array Z pinch
Sheng Liang, Qiu Meng-Tong, Hei Dong-Wei, Qiu Ai-Ci, Cong Pei-Tian, Wang Liang-Ping, Wei Fu-Li
2011, 60 (5): 055205. doi: 10.7498/aps.60.055205
Abstract +
The implosion dynamics of wire array Z pinch can be divided into four stages: (1) wire ablation; (2) formation of plasma shell; (3) implosion; (4) stagnation. Based on the optical-framing camera and the soft X-ray framing camera, lots of experiments on the early stage of wire array Z pinch and imploding dynamics have been carried out. Images of wire array Z pinch from wire ablation to plasma column breakdown were obtained. The main results were as follows: (1) There is a long ablation stage, and the wire ablation is not uniform along the axis. The imploding experimental trajectory is consistent with the phenomenological model. (2) The cathode emission is obviously observed in both optical images and X ray images. In the late stage of implosion, there is obvious trailing radiation distribution around the cathode. (3) The precursor plasma column is formed after the collision of the ablating plasma at the axis, which expands at first, then becomes compressed. (4) The temperature and ionization stage of corona plasma were estimated according to its azimuthally expanding velocity.
Design of implosion capsules with low convergence ratio driven by radiation on Shenguang Ⅱ and Shenguang Ⅲ prototype laser facilities
Jiang Shao-En, Miao Wen-Yong, Kuang Long-Yu
2011, 60 (5): 055206. doi: 10.7498/aps.60.055206
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The design method for implosion capsules with low convergence ratio driven by radiation was dweloped. These kinds of the capsules used for the experiment on Shenguang II (SG-II) and Shenguang III prototype (SG-III-P) laser facilities were simulated using Multi-1d code. The implosion targets were designed, and the variations of convergence ratio, neutron yield and area density vs fuel pressure were obtained from the simulation. Two kinds of implosion targets with low convergence ratio on SG-II which were filled with DD and DT fuels respectively and a kind of the target on SG-III-P filled with DD were designed. The neutron yield calculated by Multi-1d with low convergence ratio agreed with the experimental data on Shenguang II laser facility. It showed that Multi-1d is reliable for use with these experiments.
Quantitative study of radiation temperature for gold hohlraum on SG-Ⅱ laser facility
Li San-Wei, Song Tian-Ming, Yi Rong-Qing, Cui Yan-Li, Jiang Xiao-Hua, Wang Zhe-Bin, Yang Jia-Min, Jiang Shao-En
2011, 60 (5): 055207. doi: 10.7498/aps.60.055207
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Hohlraum radiation temperature is an important parameter for inertial confinement fusion (ICF) research. Experimental measurements of radiation temperature by a streaked optical pyrometer and a soft X-ray spectrometer (SXS) with 14 absolutely calibrated channels are performed on SG-Ⅱ laser facility,which shows that the results of the two methods agrees with each other well. With 2.1kJ laser energy and 1ns pulse width, the hohlraum radiation temperatures for small hohlraum (Φ0.8 mm×1.7 mm, LEHΦ0.38 mm) and large hohlraum (Φ1.0 mm×2.1 mm, LEHΦ0.6 mm) are 180 eV and 150 eV, respectively. Using a sampling-based method (Monte Carlo), an uncertainty analysis program-package is set-up for SXS. After precise calibration and improvements for several components in SXS, the relative uncertainty of radiation temperature is significantly reduced from 8% to 3%.
Numerical and experimental study of air arc splitting process considering splitter plate erosion
Yang Fei, Rong Ming-Zhe, Wu Yi, Shi Qiang, Liu Zeng-Chao, Ma Rui-Guang, Chen Sheng
2011, 60 (5): 055208. doi: 10.7498/aps.60.055208
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A three-dimensional magnetohydrodynamic model of an air arc plasma, considering the metal vapour from erosion of an iron splitter plate, is developed. An equation describing conservation of the iron vapour mass is added to the standard mass, momentum, and energy conservation equations. The influence of the iron vapour on the thermodynamic and transport properties of the gas mixture is considered in the calculation. The arc voltage, and distributions of temperature, gas flow, and mass fraction of iron vapour in the arc chamber are calculated and analyzed in detail. The experiment was carried out to support the simulation work. The images recorded by a high-speed camera and arc voltage measurement were compared with the predictions of the simulations, which proved the validity of the simulation model.
Analsys of the properties of tunable prohibited band gaps for two-dimensional unmagnetized plasma photonic crystals under TM mode
Liu Shao-Bin, Zhang Hai-Feng, Kong Xiang
2011, 60 (5): 055209. doi: 10.7498/aps.60.055209
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The piecewise linear current density recursive convolution (PLCDRC) on finite-difference time-domain (FDTD) method is applied to study the properties of prohibited band gaps for TM wave propagation in the two-dimensional unmagnetized plasma photonic crystal. In frequency-domain, the transmission coefficient of electromagnetic differential Gaussian pulses are computed and we analyzed the effect on properties of tunable prohibited band gaps for the two-dimensional unmagnetized plasma photonic crystals by its relative permittivity of column, lattic constant, dielectric column radius, periodic constant and parameters of plasma. The results showed that the prohibited band gaps can not be broadened by inceasing periodic constant and plasma collision frequency, but can be broadened by increasing relative permittivity of column and plasma frequency. The prohibited gaps also can be widened by decreasing the lattic constant and dielectric column radius for fill rate of a certain value.
Research on interface and fractal characteristics of PI/Al2O3Films by SAXS
Cheng Wei-Dong, Wu Zhong-Hua, Bu Wen-Bin, Fan Yong, Liu Xiao-Xu, Yin Jing-Hua
2011, 60 (5): 056101. doi: 10.7498/aps.60.056101
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Inorganic nano-composite polyimide (PI) films were prepared with the method of sol-gel. The interfacial situation and the fractal characteristics of PI films were investigated by small angle X-ray scattering (SAXS) using synchrotron radiation as X-ray source. SAXS results indicated that the scattering curves in the high-angle region have a negative slope, i.e., a negative deviation from Porod's law, which suggests that there are obvious interface layers between the organic phase and the inorganic phase in the PI films. The thicknesses of interface layers are 0.54—1.48 nm. The interaction of the organic phase and inorganic phase becomes stronger and the thickness of interfacial layer increases with the increase of inorganic nano-components. Nano-particles have mass fractal, simultaneously have surface fractal structure, and their distribution and assemblage are nonlinear dynamic processes. With the inorganic nano-components increasing, the surface fractal dimension increases and mass fractal dimension decreases, which shows that the nano-particles structure becomes looser and mass distribution becomes more uneven. The anchoring action of polymer chains is enhanced and the number of anchored point increased respectively, the surface of the hybrid PI films becomes rougher. Finally, according to the interface characteristics of hybrid PI films, the relationship of the breakdown field strength with component is analyzed by percolation theory and polarization theory.
Distributed-feedback lasing from dye-doped holographic polymer dispersed liquid crystal transmission grating
Liu Yong-Gang, Lu Xing-Hai, Xuan Li, Deng Shu-Peng, Li Wen-Cui, Huang Wen-Bin
2011, 60 (5): 056102. doi: 10.7498/aps.60.056102
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In this paper,we report the fabrication of dye-doped holographic polymer dispersed liquid crystal(HPDLC) transmission grating and the property of distributed-feedback lasing from dye-doped HPDLC transmission grating. Under the excitation of a frequency-doubled Nd:yttrium-aluminum-garnet laser operating at a wavelength of 532 nm, optically pumped lasing with narrow linewidth and low threshold was observed from a DCM dye-doped HPDLC transmission grating with the grating period of 586 nm. The results showed that the emitted lasing peak centered at about 603 nm with a full width at half maximum (FWHM) of only 1.4 nm, and the threshold pumping intensity was about 17.3 μJ, which is evidently lower than the previously reported values.
Molecular dynamics simulation of resonance properties of strain graphene nanoribbons
Zhang Jia-Hong, Gu Fang, Gu Bin, Yang Li-Juan
2011, 60 (5): 056103. doi: 10.7498/aps.60.056103
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Starting from the energy conversion and energy conservation law in the constant-NVE ensemble, the molecular dynamics method using the COMPASS force field was applied to investigate the dynamic properties of graphene nanoribbons (GNRs) together with the GNR-based strain sensors. The following results were obtained: (a) the nonlinear response dominates the dynamic behavior of GNRs, and their ultra-high fundamental frequencies are closely related with the length and boundary conditions; (b) the effect of uniaxial tensile strain on the fundamental frequencies of GNRs is significant and strongly depends on boundary conditions, and the GNR-based strain sensor clamped on four edges has a higher frequency shift, and its sensitivity is up to 7800 Hz / nanostrain, much higher than that of carbon nanotube-based strain sensor with the same length; (c) the resonant characteristics of GNRs and GNR-based strain sensors are insensitive to the chirality. The obtained results suggest that, through cutting the appropriate size and setting the boundary conditions, the GNRs could be used to design a new generation of nanoelectromechanical system (NEMS) resonators and strain sensors, owing to their ultra-low density and ultra-high fundamental frequencies as well as ultra-high sensitivity without considering the impact of chirality.
Influence of high-dose nitrogen implantation on the positive charge density of the buried oxide of silicon-on-insulator wafers
Zhang En-Xia, Tang Hai-Ma, Zheng Zhong-Shan, Yu Fang, Li Ning, Wang Ning-Juan, Li Guo-Hua, Ma Hong-Zhi
2011, 60 (5): 056104. doi: 10.7498/aps.60.056104
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The influence of nitrogen implantation on the properties of silicon-on-insulator buried oxide using separation by oxygen implantation was studied. Nitrogen ions were implanted into the buried oxide layer with a high-dose of 1016 cm-2. The experimental results showed that the positive charge density of the nitrogen-implanted buried oxide was obviously increased, compared with the control sampes without nitrogen implantation. It was also found that the post-implantation annealing caused an additional increase of the positive charge density in the nitrogen implanted samples. However, annealing time displayed a small effect on the positive charge density of the nitrogen implanted buried oxide, compared with the significant increase induced by nitrogen implantation. Moreover, the capacitance-voltage results showed that the positive charge density of the unannealed sample with nitrogen implanted is approximately equal to that of the sample annealed at 1100 ℃ for 2.5 h in N2 ambient, despite an additional increase brought with annealing, and the buried oxide of the sample after 0.5 h annealing has a maximum value of positive charge density. According to the simulating results, the nitrogen implantation resulted in a heavy damage to the buried oxide, a lot of silicon and oxygen vacancies were introduced in the buried oxide during implantation. However, the Fourier transform infrared spectroscopy of the samples indicates that implantation induced defects can be basically eliminated after an annealing at 1100 ℃ for 0.5 h. The increase of the positive charge density of the nitrogen implanted buried oxide is ascribed to the accumulation of implanted nitrogen near the interface of buried oxide and silicon, which caused the break of weak Si-Si bonds and the production of positive silicon ions in the silicon-rich region of the buried oxide near the interface, and this conclusion is supported by the results of secondary ion mass spectrometry.
Three-dimensional simulation of total dose effects on ultra-deep submicron devices
He Bao-Ping, Ding Li-Li, Yao Zhi-Bin, Xiao Zhi-Gang, Huang Shao-Yan, Wang Zu-Jun
2011, 60 (5): 056105. doi: 10.7498/aps.60.056105
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The radiation-induced charge distribution in shallow-trench isolation (STI) structures is analyzed in this paper. We present a new approach for modeling total dose effect of ultra-deep submicron transistors. The results show that, when there is no radiation-induced charge in top100 nm of the trench-silicon interface, the simulation results of 0.18μm ultra-deep submicron transistors show that the I-V sub-threshold does not produce the hump, and yield good agreement with experiments. On the aspect of the improvement on total ionizing dose, the leakage current of MOSFET with delta doping can be effectively reduced than with the uniform doping profile under lower radiation dose. If the Halo doping is adopted in landscape orientation, the total dose of ultra-deep submicron transistors can be improved. This improvement is evident even at higher irradiation dose.
Radition effect on Ti/4H-SiC SBD of gamma-ray,electrons and neutrons
Zhang Lin, Xiao Jian, Qiu Yang-Zhang, Cheng Hong-Liang
2011, 60 (5): 056106. doi: 10.7498/aps.60.056106
Abstract +
The Ti/4H-SiC Schottky barrier diodes(SBDs) were irradiated at room temperature with 60Co gamma-ray source, 1MeV electrons and neutrons, and 0V and -30 V bias voltage were applied to the diodes during gamma-ray and electron radiation. The meaurement results show that -30 V radiation bias voltage has no influence on the radiation effect of the diodes. After 1 Mrad(Si) gamma-ray and 1×1013 n/cm2neutron radiation respectively, the Schottky barrier height of the diodes basically remain the same values. After an electron dose of 3.43×1014 e/cm2, Schottky barrier height of the diodes slightly decreased, which was caused by ionizing damage of high energy electron, and recovered completely after annealing at room temperture. After gamma-ray and electron radiation, the reverse current of Ti/4H-SiC SBD had no obviously degration. The on-state resistance of the diodes increased after electron and neutron radiaiton.
Study on fractal features of modulated radio signal
Li Jian-Dong, Tang Zhi-Ling, Yang Xiao-Niu
2011, 60 (5): 056401. doi: 10.7498/aps.60.056401
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The shape of radio signals determined by modulation system and that produced by the nonlinear transform are different in kind, which is the basis for discriminating them. Feature extraction based on fractal theory is a new method. In this paper,the features of modulation and nonlinear transform are projected to fractal feature space by computing the variance fractal dimension and the Mandelbrot singularity spectra dimensions. The numerical result show that differences in fractal features do exist between different modulated signals and the nonlinear transformed signals. The results show that the feature of these signals can be extracted based on fractal theory, which has engineering value for the identification of modulated radio signals.
New material exploration and magnetism researchon Heusler alloys Cr-Co-Ga
Qian Jin-Feng, Feng Lin, Zhu Wei, Liu En-Ke, Tang Xiao-Dan, Wang Wen-Hong, Wu Guang-Heng, Meng Fan-Bin, Liu He-Yan, Luo Hong-Zhi
2011, 60 (5): 056402. doi: 10.7498/aps.60.056402
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The crystal structure, magnetism and transport properties of a series alloys from Co2CrGa to Cr2CoGa (Co50-xCrx+25Ga25, x=0—25) have been investigated by the experimental and KKR-CPA-LDA calculation methods. Substituting Cr for Co atoms, the crystal structure changes from L21 type to Hg2CuTi structure, which make, the lattice parameters increase about 0.69% linearly. Also, the ferromagnetic coupling turns to anti-ferromagnetic coupling, that makes the magnetic moment linearly decrease from 3.06μB to nearly zero. Through ab initio study of CPA, it has been found that the extraneous Cr atom at the A site couples anti-ferromagnetically with the Cr atom originally situated at B site with a nearly equal magnitude of magnetic moment, and the magnetic moment of Co atoms occupying the C site decreases from 0.60μB to 0.21μB through the whole substituting process. Based on the results of magnetic measurement and calculation, about 20% atomic disorder in the alloy Cr2CoGa has been confirmed, which is consistent with the observation of the X-ray examination. It is interesting that a non-linear "middle component phenomenon" has been observed in the composition dependence of both Curie temperature and the electrical resistivity. The related discussions is based on the magnetic environment change surrounding the magnetic atoms.
First principles study of interactions between Au and N atoms on SrTiO3(001) surface
Fang Li-Min
2011, 60 (5): 056801. doi: 10.7498/aps.60.056801
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First principles PWPP calculations based on the density functional theory were carried out to study the microscopic mechanism of the interaction between Au and N atoms on SrTiO3(001) surface. From analysis of the related energies and density of states, it was confirmed that there is clearly a synergy effect between the substitution of N for the surface O atoms and the adsorption of Au atoms on the SrTiO3(001) surface. In other words, the substitution of N atoms for O atoms stabilizes the Au atoms adsorbed on the surface, and the presence of the adsorbed Au atoms can also favor the process of N substitution on the surface.
Evolution of interphase misfit dislocation networks in Ni-based single crystal superalloy under shear loading
Wu Wen-Ping, Guo Ya-Fang, Wang Yue-Sheng, Xu Shuang
2011, 60 (5): 056802. doi: 10.7498/aps.60.056802
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The molecular dynamics simulation is used to study the evolution of misfit dislocation networks at γ/γ' phase interfaces of Ni-based single crystal superalloy under shear loading. From the simulation we found that the three patterns of dislocation networks on the (100), (110) and (111) phase interfaces show different degrees and patterns of damage. The deformation and damage occur easier at a higher temperature. Under the same shear loading and temperature, the square dislocation network at (100) phase interface is the most stable.
H∞ synchronization of general chaotic systems with random perturbations
Tu Li-Lan, Ke Chao, Ding Yong-Mei
2011, 60 (5): 056803. doi: 10.7498/aps.60.056803
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In this paper, the H∞ synchronization of general chaotic systems with random perturbations is investigated, in which perturbation is a random process of Brownian motion. Based on stochastic Lyapunov stability theory, linear matrix inequalities, and It formula and H∞ control method combined with feedback control laws, some new asymptotic synchronization schemes are established which guarantee robust stochastical mean square asymptotical synchronization for drive system and noise-perturbed response system, as well as achieving a prescribed stochastic robust H∞ performance level. These schemes are in a simple form and easy to work with Matlab. Finally, simulations show that the proposed results are correct and effective.
The laser induced electronic acceleration process in nanostructured dielectric
Xia Zhi-Lin
2011, 60 (5): 056804. doi: 10.7498/aps.60.056804
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The Monte Carlo method has been used to simulate the process of electron transport and acceleration in a nano-dimensional unit when irradiated by laser pulse of wavelength 1064 nm and power density of GW/cm2 level. When electrons transport in laser field, the scattering of electron-phonon and electron-surface are considered. The results show that: when the size of simulation unit is small to a degree, electron-surface scattering will dominate the scattering process and the small size effect becomes obvious. As a result, the electron is difficult to absorb laser energy. Based on the results, we can design new kind of films with nanostructure and improve the laser induced damage threshold of optical films.
The eigenvalues of quantized spin waves and theeffect of the uniaxial anisotropy
Bai Yu-Hao, Zhou Wen-Ping, Hou Xiao-Juan, Yun Guo-Hong, Bai Narsu
2011, 60 (5): 056805. doi: 10.7498/aps.60.056805
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The eigenproblems of quantized spin waves in a (100) ferromagnetic bilayer system have been investigated theoretically by using the interface rescaling approach. The energy-band structure of the system has been obtained and the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands were explored thoroughly. It is found that there are bulk modes, perfect confined modes and interface modes in the biferromagnetic system, the existing condition of which is determined not only by the bulk exchange coupling constant, the interface exchange coupling constant, the spin of lattice, the number of atomic layers, but also by the uniaxial bulk anisotropy.
Electronic structure and optical properties of Ag-doping and Zn vacancy impurities in ZnS
Li Jian-Hua, Zeng Xiang-Hua, Ji Zheng-Hua, Hu Yi-Pei, Chen Bao, Fan Yu-Pei
2011, 60 (5): 057101. doi: 10.7498/aps.60.057101
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The geometrical structures of Ag-doped ZnS, that with Zn vacancies and pure zinc blend were optimized by means of plane wave pseudo-potential method (PWP) with generalized gradient approximation (GGA). The electronic structure and optical properties of the three systems were calculated and the reason why p type ZnS is difficult to form was given theoretically. Equilibrium lattice constant, band structure, electronic structures and optical properties were discussed in detail. The results reveal that,in Ag-doped ZnS and Zn vacancy systems, due to the introduction of the defect level, the band gap is reduced and electronic transition in the visible region is obviously enhanced.
Ab initio calculation of pressure-induced phase transition of TiN polytypes
Gu Xiong, Gao Shang-Peng
2011, 60 (5): 057102. doi: 10.7498/aps.60.057102
Abstract +
Based on a plane wave pseudopotential method within the framework of density functional theory, equilibrium structure, bulk modulus, and relative stability were calculated for 6 kinds of TiN polytypes including B1 (NaCl structure), B2 (CsCl structure), B3 (zincblende structure), Bk (hexagonal BN structure), Bh (WC structure) and B81 (NiAs structure). Theoretical calculation also showed that TiN can not exist in B4 (wurtizite) structure. Through geometry optimization under hydrostatic pressure, the enthalpy of each TiN phase at different pressures was obtained. It was found that TiN with B1 structure is the most stable phase at pressure lower than about 345 GPa, whereas B2 TiN is the most stable at pressure above 345 GPa. Volume discontinuity and bulk modulus change can be observed during the transition from B1 to B2 phase.
Effect of Dy additive on microstructure and magnetic propertiesof rapidly solidified Nd-Fe-B strips
Ding Yong, Chen Ren-Jie, Guo Shuai, Liu Xing-Ming, Lee Dong, Yan A-Ru
2011, 60 (5): 057103. doi: 10.7498/aps.60.057103
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Sintered Nd-Fe-B magnets made from strip cast alloys have been studied extensively owing to their strong permanent magnetic properties. Up to now the studies mainly focus on technology parameters of strip casting, including casting temperature, wheel speed and phase transition temperature and so on. However, microstructure and properties of rapidly solidified strips could be influenced by the composition of alloy. In this work, the effects of added Dy element on microstructures and properties of Nd-Fe-B rapidly solidified strips have been investigated. The strips shad a pronounced texture of the tetragonal T1(2 ∶14 ∶1) phase as shown by the prominent (00l) peaks at wheel surface. The alignment coefficient of the strips was the highest when Dy content ranged from 1 to 2at%. This is the result of the microstructure of strips being optimized through an appropriate amount of Dy addition. At the same time, the volume fraction of isotropic crystal decreased as Dy content increased. It revealed that the oxidation speed decreased with increasing Dy content.
Nonclassical ground state for Fröhlich palaron
Luo Zhi-Hua, Yu Chao-Fan, Lin Qia-Wu
2011, 60 (5): 057104. doi: 10.7498/aps.60.057104
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Based on the variational approach proposed by Huybrecht , using the two-mode squeezed coherent state as the second-step canonical transformation, we have investigated the nonclassical ground state for the Fröhlich polaron through considering the dynamical correlation bewteen the phonon wave vectors q and q' . Due to the correlation effect between the phonon coherent state and the phonon squcezed state, caused by the two-mode squeezing effect of the phonon coherent state, the coherent parameter fq and the two-mode squeezing angle φqq' also have a big correction correspondingly. As a result , this effect has greatly enhanced the coherent effect and the squeezing angle effect . The calculation and the analysis based on the ground state energy of the polaron have shown that 1) for the weakly coupled region ,the correction ΔE(1)c due to the effect of the displaced-phonon squcezed state is comparable to the Feynma n' s path integral calculation (ΔEf) and the coherent state correetion by Huybrechts (ΔE0), while the correction (ΔE(2)c) due to the squeezing effect of the phonon coherent state has an essential contribution , i.e. ΔE(2)c«(ΔEf,ΔE0); 2) for the strongly-coupled region ,the contribution from the displaced-phonon squcezed state has a greatly reduction , ΔE(1)c≥(ΔEf,ΔE0) .Althougth, at the same time ,the contribution due to the squeezing effect of the phonon coherent state also has a greatly reduction ,we still have ΔE(2)c«(ΔEf,ΔE0).
Growth and chracterization of Zn1- x-y Na x Co y O thinfilms prepared by pulsed laser deposition
Tao Ye-Wei, Li Shi-Shuai, Feng Xiu-Peng, Huang Jin-Zhao, Liu Chun-Yan, Zhang Zhong
2011, 60 (5): 057105. doi: 10.7498/aps.60.057105
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Zn1-x-yNaxCoyO thin films were prepared by pulsed laser deposition (PLD) on Si(111) substrates. The X-ray diffraction(XRD), atomic force microscopy(AFM), fluorescence spectrometer and the Four-probe tester were used respectively to investigate the structure, surface structure, optical and electrical properties of the thin films. The optical and electrical properties of Zn1-x-yNaxCoyO doped with different Na-Co concentrations are investigated. The result indicates that the structure of films are zincite and the doping of Na-Co leads to the red-shift of the UV emission peak of ZnO. When the doping concentration of both Na and Go are 10%, the film has the highest fluoresence intensity located at 397 nm, and the lowest resistivity of 8.34×10-1 Ω ·cm is detected in this film. The reasons of above-mentioned phenomena are discussed in depth.
The Jahn-Teller effect and energy-level splitting for C2+4molecules with the D4h symmetry configuration
Feng Sheng-Qi, Qiu Qing-Chun
2011, 60 (5): 057106. doi: 10.7498/aps.60.057106
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Based on quantum theory and ligand field theory, the E×(b1g+b2g) Jahn-Teller system for C2+4 molecules with the D4h symmetry configuration was studied in this paper using the methods of group theory and symmetry analysis. The symmetry of electronic states and phonon states for the system were explored, the coupling between phonons and CG coefficients were discussed, and the vibronic Hamiltonian for the E×(b1g+b2g) Jahn-Teller system was constructed. The ground state of the system and its energy were calculated using unitary shift transformation. It was found that there were four minima on the potential energy surface of the system because of the vibronic coupling. No matter which minimum the system is in, the ground energy level of the system is split into two energy levels after the Jahn-Teller distortion and the electronic degeneracy of the system is completely lifted. The Jahn-Teller distortion direction for the system was studied further using group theory. The results show that the distortion direction of the system should be D4h→D2h, and the symmetry of the ground state for C2+4 molecules is B1uunder the group D2h after the Jahn-Teller distortion.
Effect of carrier recombination on time-resolved Faraday rotation spectroscopy in GaAs quantum wells
Teng Li-Hua, Wang Xia
2011, 60 (5): 057202. doi: 10.7498/aps.60.057202
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Based on the rate equations of a two-level system, time-resolved Faraday rotation spectroscopy model was developed. It was found that the carrier recombination has strong effect on the decay of Faraday rotation signal. The model was also used to fit the Faraday rotation spectra measured in GaAs quantum wells. The electron spin relaxation time was obtained as 73.5 ps. However, the spin relaxation time was obtained only as 51.3 ps with the single exponent to fit the Faraday rotation spectra. Thus, the conventional method with the single exponent to fit the Faraday rotation spectra is inaccurate.
Propagation properties of a surface plasmonicwaveguide with a bowtie air cores
Jia Zhi-Xin, Duan Xin, Lü Ting-Ting, Guo Ya-Nan, Xue Wen-Rui
2011, 60 (5): 057301. doi: 10.7498/aps.60.057301
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A kind of surface plasmonic waveguide with a bowtie shaped air core was designed. The dependence of distribution of longitudinal energy flux density, effective index and propagation length of the fundamental mode supported by this waveguide on geometrical parameters and working wavelength were analyzed using the finite-difference frequency-domain (FDFD) method. Results show that the longitudinal energy flux density distributes mainly in the center region which is formed by the top and the bottom ridge. The effective index and propagation length of the fundamental mode can be adjusted by the geometric parameters as well as the working wavelength. At a given working wavelength, the effective index decreases as the radius of ridge increases, meanwhile propagation length and mode area of the fundamental mode increase as radius of ridge increases. The geometric parameter of radius of circles at four corner can affect the propagation properties slightly. The radius of sectors on both sides can effect propagation properties obviously. With given geometric parameters, relative to the case of λ=705.0 nm, in the case of larger λ, the area of field distribution is larger, and the size of the contact area of field and metallic surface is also larger, then the interaction of field and silver is weaker, and the effective index becomes smaller, so the propagation length becomes larger. The possibility of applying this kind of surface plasmonic waveguide to the field of sensors was discussed.
Influence of interdot-coupling on differentialconductance for a triple quantum dot
Ju Xin, Guo Jian-Hong
2011, 60 (5): 057302. doi: 10.7498/aps.60.057302
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Using the method of equation of motion of nonequilibrium Green's function, we study the Aharonov-Bohm effect of differential conductance of electronic transport through a triple quantum dot system in which two quantum dots are directly coupled to the electrodes. We found that the conductance or tunneling property depends on the different values of local density of states. Moreover, electron transport through the system can be influenced by inter-dot coupling and energy level of each dot.
Electrical properties of the metal/porous silicon/Si(M/PS/Si) microstructure
Sun Peng, Hu Ming, Liu Bo, Sun Feng-Yun, Xu Lu-Jia
2011, 60 (5): 057303. doi: 10.7498/aps.60.057303
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In this paper, porous silicon (PS) was prepared in a double-tank cell using the electrochemical corrosion method. Subsequently, different metal films for electrical contacts were deposited on the PS samples by magnetron sputtering to form the M/PS/Si microstructure. The PS surface morphology was characterized by SEM. The electrical properties of the M/PS/Si microstructure were studied through the I-V characteristic tests. It was shown that Pt can form ohmic contact with PS. The I-V characteristic curves were formed from two parts:linear part and nonlinear part. However, Cu formed Schottky contact with PS and its I-V curves showed rectification characteristics. The rectification ratio decreased when the porosity of the PS increased.
Double screen frequency selective surface structure optimized by genetic algorithm
Wang Jian-Bo, Lu Jun
2011, 60 (5): 057304. doi: 10.7498/aps.60.057304
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Double screen frequency selective surface(FSS) is a very effective means of realizing the invisibility of radar-cabin from the detection of radar wave since it can well realize the flattened effect and rapid decrease. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm(GA) when electromagnetic waves are incident on the double screen FSS at varying angles, and an optimized FSS structure and transmission characteristics are obtained. Meanwhile, the relevant experimental samples are prepared by means of coating and lithography and are tested in microwave anechoic chamber. The results show that the optimized structure has a better stability with respect to incident angle of electromagnetic wave under the condition of 2GHz operation, thereby laying the foundation for the application of double screen FSS to curved surfaces at wide angles.
Electronic density distribution of La0.55Ca0.45MnO3 revealed by temperature-dependent X-ray diffraction
Yue Ting, He Hao, Zhang Xing, Li Guang
2011, 60 (5): 057501. doi: 10.7498/aps.60.057501
Abstract +
The temperature-dependent spatial structure of perovskite oxide La0.55Ca0.45MnO3 has been checked by X-ray diffraction (XRD) and Rietveld method was employed to refine the XRD data. It was found that with the decrease of temperature, almost all of the diffraction peaks were split; each peak was divided from single peak at high temperature into two peaks at low temperature, indicating the appearance of a crystalline structural phase transition. Corresponding to the structural phase transition, magnetization measurements also revealed a magnetic transition from ferromagnetism to antiferromagnetism. With the Rietica analysis of the XRD data of the compound, plots of the electronic density distribution of La0.55Ca0.45MnO3 were made. Sharp difference in the distributions above and below the transition temperature was clearly shown. Taking the magnetism of the compound into consideration, the structural phase transition was analyzed and the sharp difference of the electronic density distribution was qualitatively explained.
Microstructures and magnetic analyses of Al/ZnO/Al thin films
Liu Li-Hu, Zhang Hai-Feng, Xu Qin, Sun Hui-Yuan, Qi Yun-Kai, Gu Jian-Jun
2011, 60 (5): 057502. doi: 10.7498/aps.60.057502
Abstract +
Al/ZnO/Al thin films are prepared on the glass substrates by dc magnetron sputtering and annealed in vacuum and atmosphere, separately. The crystal structures are analyzed by X-ray diffraction (XRD), and the magnetic properties are measured by a Physical Properties Measurement System (PPMS) with a magnetic field parallel to the films plane. The XRD results indicate that the microstructures of thin films are greatly influenced by the annealing aura. In this paper, an improved corrected method to subtract the signal of the substrate is suggested. Simultaneously, the maximum fitting error of substrate is calculated, and the magnetic properties of the modified films are discussed. The results show that the room temperature ferromagnetism may be related to the charge transfer between Al and Zn and the variational position of Al in ZnO films in different annealing conditions.
Study on resonance magnetoelectric effect of layeredNi/Pb(Zr,Ti)O3/TbFe2 composites
Bi Ke, Ai Qian-Wei, Yang Lu, Wu Wei, Wang Yin-Gang
2011, 60 (5): 057503. doi: 10.7498/aps.60.057503
Abstract +
Layered magnetoelectric Ni/PZT/TbFe2 composites have been prepared by electroless deposition and bonding method. The influence of the Ni layer thickness on ME coupling and resonance frequency is discussed. The results show that the magnetoelectric coefficient of Ni/PZT/TbFe2 composites changes differently from that of other composites and two remarkable resonance peaks have been observed. The magnetoelectric voltage coefficient at the first-order longitudinal resonance mode increases as the Ni layer thickness increases. Both experimental and calculated data reveal that the first-order bending resonance frequency fr1 and longitudinal resonance frequency fr2 increase with the Ni layer thickness.
Measurement of magnetic anisotropyby ferromagnetic resonance
Gu Wen-Juan, Pan Jing, Du Wei, Hu Jing-Guo
2011, 60 (5): 057601. doi: 10.7498/aps.60.057601
Abstract +
The effective magnetic field caused by exchange coupling between a ferromagnetic and an antiferromagnetic bilayer and its magnetic anisotropy have been investigated by means of ferromagnetic resonance. It was shown that the exchange bias phenomenon occurrence and its positive or negative characteristic for ferromagnetic/antiferromagnetic bilayer can be identified from its magnetic resonance spectrum. In addition, when the field was applied along different crystalline directions, the behavior of magnetic resonance field will be changed, and is closely dependent on the magnetocrystalline anisotropy and unidirectional anisotropy induced by the interface coupling in ferromagnetic/antiferromagnetic bilayer. Anomalies in the ferromagnetic resonance frequency studied as functions of applied field, including its orientation and strength, are interpreted as evidence for the four fold anisotropy and unidirectional anisotropy. Our conclusions are in good agreement with the related experiments.
Failure mechanism of PZT 95/5 under direct currentand pulsed electric field
Zhang Fu-Ping, Du Jin-Mei, Liu Yu-Sheng, Liu Yi, Liu Gao-Min, He Hong-Liang
2011, 60 (5): 057701. doi: 10.7498/aps.60.057701
Abstract +
The failure mechanism of PZT 95/5 under direct current and pulsed electric field is studied by experiment and theoretical analysis in this paper. The electrothermal coupled failure is the key mode when the PZT 95/5 is subjected to direct current. But when the pulsed electric field is applied to the PZT 95/5, the resonance effect and the relation between energy and frequency being considered, the vibrant energy shifts to high frequency and the possibility of electromechanical-coupled failure is increased with decreasing pulse duration. When the pulse duration is increased, the failure behavior transfers gradually from mechanical coupled with electric failure to direct current failure mode.
Metal organic decomposition technique and optical propertiesof amorphous Ba0.7Sr0.3TiO3 thin films
Peng Jing, Dong Ze-Hua, Xu Zhi-Mou, Wang Shang-Bao
2011, 60 (5): 057702. doi: 10.7498/aps.60.057702
Abstract +
With the development of Si-based optical integrated circuit, much attention has been paid to the crystalline and amorphous (BaxSr1-x)TiO3(BST) films due to its good optical properties. In this study, the amorphous Ba0.7Sr0.3TiO3 (BST0.7) thin films were grown on the fused quartz and silicon substrates at low temperature by using a metal organic decomposition (MOD)-spin-coating procedure from barium 2-caprylate Ba(C8H15O2)2 and 3-methylbutyl acetate CH3COOC2H4CH(CH3)2-based special precursors. The optical constants of amorphous BST0.7 thin films including refractive index, extinction coefficient and optical band gap energies were presented. Photoluminescence spectra of BST0.7 films were also observed. The calculated extinction coefficient of 214-nm-thick amorphous BST0.7 thin films in visible and near-infrared region was of the order of 10-3, which is much lower than that of polycrystalline BST thin films. The optical band gap energy and refractive index n were estimated to be about 4.27 eV and n=1.94, respectively. Intensive photoluminescence at room temperature was achieved in the 520 to 610 nm wavelength range with a strong visible peak at 540—570 nm when excited by 450 nm laser light. No photoluminescence was observed in crystalline BST0.7 thin films.
Theoretical study and numerical verification of terahertz radiation emitted by carbon nanotubes
Wu Yu-Ming, Le Li-Wei, Wang Yan, Wang Dong-Xing, Fu Jia-Hui, Wang Yue, Wu Qun
2011, 60 (5): 057801. doi: 10.7498/aps.60.057801
Abstract +
Based on the theory of simple tight-binding, the electronic energy structure of carbon nanotubes has been obtained under the quantitative periodic boundary condition of the carbon nanotubes. Terahertz radiation emitted by carbon nanotubes was demonstrated theoretically by adopting the reported experimental results of the interaction between electron and phonon. The numerical results verify that the carbon nanotubs can generate terahertz radiation and the reason of the terahertz oscillation was analyzed. All results provide a sound theoretical basis for using carbon nanotubes to generate terahertz wave in the experiments.
Study on the surface morphology and absorptivity of light-absorbing materials
Liang Jing-Qiu, Liang Zhong-Zhu, Zhu Wan-Bin, Su Fa-Gang
2011, 60 (5): 057802. doi: 10.7498/aps.60.057802
Abstract +
Different types of surface morphology have different effects on multiple reflection of optical materials for absorbing light and have significant influence on absorptivity of materials. A suitable surface morphology can increase the effective absorptivity of optical materials. In this paper, we simulate the multiple reflection effects of V-shaped surface, Sine-shape surface, normal or uniform obliquity distribution surface and normal height distribution surface with the ray tracing method, and then analyse the capabilities of increasing the absorbtivity and the characteristics of incident angle of light on the four types of surfaces. The common necessary condition for increasing absorbtivity of these surfaces is obtained by obliquity analysis, i.e. the mean obliquity of the surface should be larger than 30 degrees at least, and the advantages of the V-shape surface to increase absorptivity under normal incidence are analysed.
Molecular dynamics simulation of energy exchange during hydrogen collision with graphite sheet containing a vacancy
Li Shou-Yang, Sun Ji-Zhong, Zhang Zhi-Hai, Liu Sheng-Guang, Wang De-Zhen
2011, 60 (5): 057901. doi: 10.7498/aps.60.057901
Abstract +
Molecular dynamics simulation is applied to investigation of energy exchanges during hydrogen collision with graphite sheet containing a vacancy. The effects of the monovancancy defect on the energy exchanges are discussed in detail. This paper analyzes the energy loss of the incident hydrogen atom, the energy range for the adsorption process, and the energy transfer process for target atom, in the course of a hydrogen atom bombarding the carbon atom at the edge of monovacancy defect in the graphite sheet. The simulation results show that the adsorption process proceeds more easily when the graphite sheet contains a vacancy than when the graphite sheet has perfect crystalline structure. In certain areas of the graphite sheet, adsorption of an incident hydrogen atom can occur in two energy ranges. The sp2 structure as well as overhang configuration occurs when a hydrogen atom is adsorbed. This adsorption process does not reduce the C—C bond energy. It is found that the carbon atom at the edge of monovacancy defect can adsorb an incident hydrogen atom more easily but can not diffuse the gained energy as efficiently as in a perfect graphite sheet. These results are helpful for understanding the chemical erosion of carbon based materials and the ensuing tritium retention in fusion devices.
Study of spectral response for transmission-modeNEA GaN photocathodes
Du Xiao-Qing, Wang Xiao-Hui, Chang Ben-Kang, Qian Yun-Sheng, Gao Pin, Zhang Yi-Jun, Qiao Jian-Liang
2011, 60 (5): 057902. doi: 10.7498/aps.60.057902
Abstract +
Transmission-mode GaN photocathodes with the emission layer thickness of 150 nm and the doping concentration of 1.6×1017 cm-3 were grown by metal-organic chemical vapor deposition (MOCVD) and were activated in ultra-high vacuum system. The result was tested by Multi-information test system. The shape of transmission-mode NEA GaN photocathode quantum yield curves looks like the Chinese charocter 门 for "door", the photocathode had flat and high response between 255 and 355 nm, the highest quantum yield of 13% appeared at 290 nm. When the wavelength was less than 255 nm the quantum yield was decreased because of the high absorption coefficient of AlN buffer layer at short wavelengths. The quantum yield was also decreased beyond 355 nm and fell to 3.5% at the threshold of 365 nm, the quantum yield at 385 nm was reduced to 0.1% and the cut-off character of long wave was well shown. The quantum yield formula of transmission-mode GaN photocathode has been solved from diffusion equations, and the main factors affecting the quantum yield mostly, including electron diffusion length, electron escape probability, active-layer thickness and the back-interface recombination velocity, were analysed and discussed. The future work is optimizing the structure of the photocathodes.
Photoemission stability of negative electronaffinity GaN phtocathode
Guo Xiang-Yang, Chang Ben-Kang, Wang Xiao-Hui, Zhang Yi-Jun, Yang Ming
2011, 60 (5): 058101. doi: 10.7498/aps.60.058101
Abstract +
The spectral response and quantum yield curve of reflection mode GaN photocathode just after Cs, O activation and Cs reactivation was achieved by using the online multi-information measurement and evaluation system. Also the attenuation in photocurrent under the radiation of 300 nm light is measured every hour.The result indicates that GaN photcathdoe are much more stable than narrow band material. The photocurrent peak increased by 16.8% after Cs reactivation which demonstrates the reason of the QE attenuation is the Cs desorption on the Cs, O adlayer of surface. This can be explained by a double dipole layer model :Cs-O whose stability determines the stability of GaN photocathode.
Synthesis and characterization of the grinding compoundlevel diamond by pure Fe catalyst
Ying Zhang, Cao Jian-Ming, Tian Li-Fei, Qin Jie-Ming
2011, 60 (5): 058102. doi: 10.7498/aps.60.058102
Abstract +
The synthesis process of grinding compound level diamond by the pure Fe catalyst-graphite system under high temperature and high pressure was reported, and the P-T phase diagram was given. On this basis, the colorless and transparent grinding compound level diamond was synthesized through the adjustment of technical parameters. By controlling the growth speed of recrystallization of graphite and diamond, and the problem of diamond being opaque and presence of inclusions when synthesized by the pure Fe catalyst was solved. According to the analysis of Mmössbauer and Fourier infrared spectroscopy, the inclusions and content of nitrogen element were characterized. Based on clarifying the formation mechanism of inclusions, the solutions to reducing inclusions were achieved. It also demonstrated the reason why the color of diamond synthesized by the pure Fe catalyst turned tinted.
Modeling of regular eutectic growth of binary alloy basedon cellular automaton method
Wu Meng-Wu, Xiong Shou-Mei
2011, 60 (5): 058103. doi: 10.7498/aps.60.058103
Abstract +
Based on cellular automaton method, a numerical model was developed for the regular eutectic growth of binary alloy. By coupling with the macro-temperature field and considering the solute diffusion, the constitutional undercooling and the curvature undercooling, modeling of the steady-state lamellar eutectic growth was achieved. A systematic investigation on eutectic growth morphology and lamellar spacing of a model alloy was made under unidirectional solidification conditions with different undercoolings, initial lamellar spacings, temperature gradients and solidification rates. The results reproduced the adjustment of lamellar spacing of two eutectic phases under the interaction between solute diffusion and surface energy by mechanisms of nucleation, lamellar branching, lamellar termination and overgrowth. The simulated results were in agreement with those predicted by the Jackson-Hunt model and experimental results by other researchers. Finally, the model was extended to three dimensional systems, which verified its feasibility of modeling the three-dimensional eutectic growth.
A method of color modulation based on porous alumina and atomic layer deposition
Wang Xu-Long-Qi, Zhang Dong-Xian, Zhang Hai-Jun
2011, 60 (5): 058104. doi: 10.7498/aps.60.058104
Abstract +
By modeling and analyzing porous alumina (PA), a method to modulate the colors of PA templates is proposed, which is based on the preparation of PA templates and the atomic layer deposition (ALD) technique. Referring to the experimentally prepared PA samples, theoretical simulations are carried out for a series of PA templates with the same hole-diameter and hole-interval, but with different hole-depths. The relationship between the modulated colors and the hole-depths are thus disclosed. By controlling the time of anodization in oxalic acidsolution, two PA samples with different hole-depths (296 nm and 373 nm) were prepared, both with an average hole-diameter of 40 nm and an average hole-interval of 100 nm, respectively. ALD processing is then applied to deposit a layer of Fe2O3 film with total thickness of 16.8 nm on these samples. It was experimentally observed that the processed PA samples show different colors which change with hole-depths. The experimental results are in good agreement with the theoretical simulations, which proves the feasibility of color modulation with this method.
Investigation of electrochemical performances of ZnFe2O4 prepared by solid state and hydrothermal method
Bai Ying, Ding Ling-Hong, Zhang Wei-Feng
2011, 60 (5): 058201. doi: 10.7498/aps.60.058201
Abstract +
Spinel structure ZnFe2O4 were prepared by solid state reaction and hydrothermal method. Investigations on X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific area measuements indicate that the samples are well-crystallized cubic spinel structre with average particle sizes of 500 nm and 200 nm and specific areas of 136.7 m2 g-1 and 382.5 m2 g-1 for solid state reaction and hydrothermal method, respectively. The ZnFe2O4 samples show high lithium-storage capacity and good reversibility. Compared with the sample prepared by solid state reaction, ZnFe2O4 prepared by hydrothermal method demonstrate better electrochemical performances. Its specific charge capacity decays from 750 mAh g-1 to 702 mAh g-1 after 30 cycles, with capacity retention of 93.6 %. ZnFe2O4 is a very promising anode material for lithium ion battery for its easy preparation, low coat and good electrochemical performances.
Analysis of multi-switching period oscillation phenomenon in constant on-time controlled buck converter
Wang Jin-Ping, Xu Jian-Ping, Xu Yang-Jun
2011, 60 (5): 058401. doi: 10.7498/aps.60.058401
Abstract +
In this paper, multi-switching period oscillation phenomenon in constant on-time (COT) controlled buck converter is studied, and the effect of output capacitor equivalent series resistance (ESR) on the control performance of COT controlled buck converter is revealed. The study results indicate that ESR is the critical factor causing multi-switching period oscillation phenomenon in the COT controlled buck converter, and critical value of ESR is obtained. When the value of ESR is less than the critical value, the multi-switching period oscillation phenomenon occurs, and it disappears when the value of ESR is higher than the critical value. Finally, the theoretical results are verified by simulation.
A two-dimensional subthreshold current model for fullydepleted strained-SOI MOSFET
Qin Shan-Shan, Zhang He-Ming, Hu Hui-Yong, Qu Jiang-Tao, Wang Guan-Yu, Xiao Qing, Shu Yu
2011, 60 (5): 058501. doi: 10.7498/aps.60.058501
Abstract +
An analytical model for the subthreshold current of fully depleted strained -SOI MOSFET was developed by solving the two-dimensional (2D) Poisson equation and the conventional drift-diffusion theory. Model verification was carried out using the 2D device simulator ISE. Good agreement was obtained between the model's calculations and the simulated results. By analyzing the model, the dependence of current on the strained Si layer strain, thickness and doping was studied. This subthreshold current model provides valuable reference to the FD-SSOI MOSFET design.
Threshold voltage model for quantum-well channelpMOSFET with poly SiGe gate
Qu Jiang-Tao, Zhang He-Ming, Wang Guan-Yu, Wang Xiao-Yan, Hu Hui-Yong
2011, 60 (5): 058502. doi: 10.7498/aps.60.058502
Abstract +
In this paper, threshold voltage model of quantum-well channel pMOSFET with p+polycrystalline SiGe gate and its cut-in voltage model were established based on solving Poisson equation while considering the impact of free carrier. The effects of relevant parameters (Ge concentration of poly SiGe gate, Ge concentration of quantum-well SiGe channel, thickness of oxide layer, thickness of Si cap layer, doping content of quantum-well SiGe channel, and doping content of substrate) on threshold voltage and cut-in voltage of the parasitic channel was analysed by numerical analysis, and obtained the methods to restrain the opening of parasitic channel. The results of the models are in good agreement wih that of experiment reported as well as of ISE simulation.
Inserting various cathodic buffer layers to enhancethe performance of Pentacene/C60based organic solar cells
Xu Zheng, Zhao Su-Ling, Zhang Fu-Jun, Kong Chao, Cao Wen-Zhe, Gong Wei, Liu Rui, Cao Xiao-Ning
2011, 60 (5): 058801. doi: 10.7498/aps.60.058801
Abstract +
Devices with the structure of ITO/Pentacene/C60/Al were prepared. Then, in order to enhance the performance of these cells and study the mechanism of the cathodic buffer layer, bathocuproine (BCP) of different thickness were inserted between C60 and Al. When inserting 10 nm BCP, the power conversion effciency of the cell is as high as 0.46%. On this basis, bathophenanthroline (Bphen) and 3, 4, 9, 10-Perylenetetracarb-oxylicdianhydride (PTCDA) are used instead of BCP, so as to compare and discuss the effects on the performance of the solar cells caused by the electron mobility and optical absorption properties of the cathodic buffer layers. As the electron mobility of Bphen is two orders of magnitude higher than that of BCP, the efficiency of devices with Bphen as the buffer layer was improved to 0.56%. Furthermore, the absorption spectrum of devices was obviously enhanced by inserting PTCDA material which has large absorption in visible light region, and the highest current density of such device was enhanced to 5.97 mA/cm2 and the efficiency was 0.87%.
Network statistical analysis in peer-to-peer application
Li Yi-Peng, Ren Yong, Yuan Jian, Wang Yue, Shan Xiu-Ming, Huang Xiao-Hong
2011, 60 (5): 058901. doi: 10.7498/aps.60.058901
Abstract +
The rich statistical characteristics in peer-to-peer (p2p) network have recently attracted much research interest. This paper reveals the internal network statistical characteristics in the user network and resource network, both of which are abstracted from the real application downloading logs. The two-segment degree and weight distribution of user nodes indicate the dynamic of p2p users, and the similar power-law distribution of resource nodes shows the popularity diversity. Furthermore, we found that these two networks have the inherent cluster structure, only minority of clusters contain a large number of nodes, and the majority have fewer nodes in it. In user network, users in the same cluster have similar file-sharing interest, in contrast to the different user interest between clusters; meanwhile, there are obvious correlations between different resource categories in resource clusters.
The influence of U-turn movement on the dynamics of traffic flow
Guo Hong-Wei, Gao Zi-You, Xie Dong-Fan
2011, 60 (5): 058902. doi: 10.7498/aps.60.058902
Abstract +
U-turn movement is a common form of traffic organization in urban streets. A traffic flow model for U-turn movement based on the NaSch cellular automaton model is proposed to simulate and analyze the dynamics of U-turn movement. The results indicated that the U-turn movement has significant effect on the traffic flow, and it is a typical bottleneck. The U-turn movement can cause phase transition at small probability of vehicle generation and the critical flow also decreases obviously. The system with two U-turn movement is different from the system with one U-turn movement in traffic features such as phase transition and critical flux. The one U-turn system has a good performance. It is suggested that the system with a couple of U-turns may help mitigate the negative effect of U-turn movement in traffic planning and management.
A evolving network model generated by random walk and policy attachment
Jiang Zhi-Hong, Wang Hui, Gao Chao
2011, 60 (5): 058903. doi: 10.7498/aps.60.058903
Abstract +
Real-world networks always present some complex network properties simultaneously, such as small-world, scale-free, high clustering and assortative/disassortative mixing, etc. , but only part of these properties can be reproduced in most of complex network models. In this paper, a new complex network model generated by random walk and policy attachment(RAPA) is proposed. A new peer constructs a local world by random walking, and attaches itself to peers in the local world following the policy of "random selection", "poverty alleviation" or "favoring the rich". The results of analysis computing and simulation demonstrate that RAPA model can reproduce not only small-world and scale-free features, but some non-power-law features such as exponential cutoff and saturation for small variables. In addition to these, RAPA model also constructs some networks with evident clustering structure and assortative/disassortative mixing pattern.
An investigation into the expression of potential vorticity in the common meteorological coordinate systems
Zhou Xiao-Gang, Liu Shi-Jun, Wang Xiu-Ming, Tao Zu-Yu
2011, 60 (5): 059201. doi: 10.7498/aps.60.059201
Abstract +
The potential vorticity theory and diagnostic techniques are based on the potential vorticity equation and expression in the common meteorological coordinate systems. In this paper, the potential vorticity equation and expression in the isobaric and isoentropic coordinates are gotten via coordinate transformation with the two methods. First, starting from the three-dimensional vector motion equation, the potential vorticity equations and expressions are gotten by the combination of the three-dimensional vorticity equation, continuity equation, and thermodynamic equation. Second, the potential vorticity equations and expressions are directly gotten from the corresponding scalar motion equations in the isobaric and isoentropic coordinates. The results show that potential vorticity expression is different with one method from that with the other in the isobaric coordinate system, and it is the same as each other in the isoentropic coordinate system. It was found, based on further analysis of the physical nature of the coordinates, that the isobaric and isoentropic coordinates are essentially treated as a mathematical coordinate system with the first method despite the coordinate transformation made for the term of pressure gradient force in the vector motion equation. From the procedure for the second method it is clearly seen that the isobaric and isoentropic coordinate systems are the physical coordinate system under the assumption of static equilibrium, which are not simply used as a mathematical coordinate system. As far as the isobaric coordinate is concerned, only the potential vorticity equation obtained from the scalar motion equations is the strict potential vorticity equation. As for the isoentropic coordinate, owing to the potential temperature gradient perpendicular to the isoentropic plane, the potential vorticity equation and expression are the same regardless of the coordinate being viewed as the physical or the mathematical.
A new ldea of cloud motion wind derived from satellite images
Long Zhi-Yong, Shi Han-Qing, Huang Si-Xun
2011, 60 (5): 059202. doi: 10.7498/aps.60.059202
Abstract +
In this paper we firstly use a new method——numerical differentiation, which was developed in recent years to calculate gray gradient, and then realize the inverse cloud motion wind by regularization. At last, through simulation and practical experiments, we compared the wind inverse results between the algorithms with or without gray gradient information when the cloud images include perturbation. The experimental results show that the new algorithm with gradient information can reduce the influence of image disturbance effectively, and also increase the precision of cloud motion winds. We are in a position to find a new way to cloud motion wind inversion.
Atmospheric physical characteristics of dew formation in semi-arid in loess plateau
Wang Sheng, Zhang Qiang
2011, 60 (5): 059203. doi: 10.7498/aps.60.059203
Abstract +
Based on the data measured in 2009 in the DingXi, a typical semi-arid region in loess plateau, the temporal variation of condensed water and the influence factors are investigated. Meanwhile, the measurements of condensed water, made by weighing approach and eddy-correlation approach separately, are compared in this work. The results show that in the semi-arid regions in Loess Plateau, the daily maximum amount of condensation can reach 0.33 mm, the daily minimum recorded is 0.09 mm, and the average daily amount is 0.23mm. No obvious correlations is found between the amount of condensation and wind velocity, relative humidity, temperature, or land-air temperature difference. In the process of dew formation, the relative humidity which supplies the water vapor for condensing is an internal factor. The temperature which is motive power for condensing process is a key factor. The wind speed has an important effect and is an uncertain factor, which promotes but also can restrain the dew formation. It is also found that the following conditions favor the condensation process: wind speed of 0.5—2 m/s, relative humidity> 80% and land-air temperature difference <± 2℃.
Extraction algorithm for retrieving the effective constitutive parameters of metamaterials based on TE10 rectangular waveguide
Gong Jian-Qiang, Liang Chang-Hong
2011, 60 (5): 059204. doi: 10.7498/aps.60.059204
Abstract +
A novel retrieval method of the effective constitutive parameters of metamaterials based on TE10 rectangular waveguide is proposed, which is adopted to extract effective relative permittivity ε and permeability μ for the composite ferrite and wire array metamaterial in multiple symmetrical unit cell configuration. Much attention has been paid to choose the correct branch of the real part of the propagation constant β for the metamaterial with multiple unit cells, and in terms of the relationship between the measured values and theoretical values in the measurement theory, β values in the case of multiple unit cells are determined by taking the extracted β values for a single unit cell as the measured values for the multiple unit cells case. Owing to the coupling effect between the unit cells of the metamaterial with multiple unit cells, the electromagnetic wave mainly behaves as the periodic Bloch wave, which is usually negligible for a single unit cell, so the extracted effective constitutive parameters for a single unit cell generally can not be assigned as those for the metamaterial with multiple unit cells directly. However, β values for a single unit cell is generally prone to be extracted, which can be the first step to extract the β values in multiple unit cells case. It is pointed out that the extracted effective constitutive parameters can be physically meaningful only if attenuation coefficients of higher Bloch wave modes are larger than that of the fundamental Bloch mode in the periodic metamaterial, and under this condition, higher Bloch wave modes will get further attenuated with increase of the unit cell number, leaving only the fundamental mode propagation, which makes the extracted ε and μ more stable and convergent.
Information communication of the northern hemisphere on intra-seasonal and over inter-annual oscillation signals
Feng Ai-Xia, Wang Qi-Guang, Sun Shu-Peng, Gong Zhi-Qiang, Feng Guo-Lin
2011, 60 (5): 059205. doi: 10.7498/aps.60.059205
Abstract +
Basic characteristics and form of intra-seasonal and over inter-annual variations were extracted through filtering using the reanalysis data of monthly geopotential height from NCEP/NCAR. Then information theory was applied to the filtered data to analyze the communication among the intra-systems between the low and mid-high latitudes. The results were found that the information loss rate of intra-seasonal oscillation signal is higher than that of over inter-annual signal, and the directions of two signals’ communication are opposite in particular regions. The information loss rate at low latitudes is higher than that at mid-high latitudes for both time scale signals, and it is distinct between the lands and the oceans in meridional average. With respect to the altitudes, the information loss rate of over inter-annual oscillation signal at low latitudes is rather high, but it is low at mid-high latitudes over all troposphere and bottom of stratosphere. For the intra-seasonal oscillation signal, the information loss rate is high at low altitude but low at high altitude. The study of communication between the low latitude and mid-high latitude of the circulation system on the two time scales provides a new way to understand the predictability and interaction of different parts in the climate system.