Vol. 62, No. 11 (2013)
Effects of low-temperature annealing phosphorous gettering process on the electrical properties of multi-crystalline silicon with a low minority carrier lifetime
2013, 62 (11): 110101. doi: 10.7498/aps.62.110101
A new low-temperature annealing phosphorous gettering process (LTAPGP) was developed to improve the electrical properties of multi-crystalline silicon which has a low minority carrier lifetime. LTAPGP combined a multi-plateau temperature phosphorous gettering process and a low-temperature annealing process. LTAPGP can remove the iron impurities and crystallographic defects of multi-crystalline silicon, and improve the electrical properties of silicon solar cells that were produced from low minority carrier lifetime silicon wafers. Compared with multi-plateau and two-plateau temperature phosphorous gettering process, LTAPGP was more effective in gettering iron impurities and repairing crystallographic defects. The multi-crystalline silicon wafers with a low minority carrier lifetime went through an LTAPGP process were utilized to produce solar cells. The IV-measurement data prove that the efficiency of the new solar cells is 0.2% higher than that of specimens subject to the multi-plateau and two-plateau temperature processes. The results indicat that LTAPGP can make the low minority carrier lifetime silicon wafers to be used in solar cell industry, improve the utilization ratio and reduce the production cost of cast polysilicon.
A type of the new exact and approximate conserved quantity deduced from Mei symmetry for a weakly nonholonomic system
2013, 62 (11): 110201. doi: 10.7498/aps.62.110201
A type of structural equation, new exact and approximate conserved quantity which are deduced from Mei symmetry of Lagrange equations for a weakly nonholonomic system, are investigated. First, Lagrange equations of weakly nonholonomic system are established. Next, under the infinitesimal transformations of Lie groups, the definition and the criterion of Mei symmetry for Lagrange equations in weakly nonholonomic systems and its first-degree approximate holonomic system are given. And then, the expressions of new structural equation and new exact and approximate conserved quantities of Mei symmetry for Lagrange equations in weakly nonholonomic systems are obtained. Finelly, an example is given to study the question of the exact and the approximate new conserved quantities.
2013, 62 (11): 110202. doi: 10.7498/aps.62.110202
A class of transfer models for femtosecond pulse laser on nano metal film has been investigated. First, we solve the reduced solution. And then, the arbitrary order asymptotic solution of corresponding model is obtained by using the perturbation theory and method. Finally, the behavior of the solution is discussed.
2013, 62 (11): 110203. doi: 10.7498/aps.62.110203
Meshfree smoothed particle method has great advantages in dealing with nonlinear problems of solid structures However, due to the instability and poor accuracy, it has been limited to the application in solid mechanics for a long time; especially the study on shell structure with smoothed particle method is even rarely reported on account of expensive three-dimensional continuum modeling and the phenomenon of numerical fracture in the traditional method The moving least square function and total Lagrangian equations are introduced as an approximation function and approximation equations respectively to improve the stability and numerical accuracy of smoothed particle method; on this basis, the method of static analysis is proposed, and meanwhile the dynamic analysis method is also refined. Finally, the internationally recognized standard test models on static and dynamic problems are adopted to verify the above shell theory, and the results are in good agreement with the existing data, which proves the validity and reliability of the present numerical model. This paper aims to provide a reference for the further research of smoothed particle method on nonlinear shell structures, such as crack, crushing, etc.
A molecular dynamics simulation on the relationship between contact angle and solid-liquid interfacial thermal resistance
2013, 62 (11): 110204. doi: 10.7498/aps.62.110204
With the fast development of nanotechnology, the solid-liquid interfacial thermal resistance draws increasing research interest due to its importance in nanoscale energy transport. The contact angle is an important quantity characterizing the interfacial properties and is easy to be measured experimentally. Previous researchers have tried to correlate the contact angle to the interfacial thermal resistance. Using molecular dynamics simulation, we have calculated the contact angle and interfacial thermal resistance at a solid/liquid interface and discuss the relationship between the two quantities. The solid/liquid bonding strength and the solid properties are varied to test their effects on both contact angle and interfacial thermal resistance. The simulation results demonstrate that with increasing solid/liquid bonding strength, both the contact angle and interfacial thermal resistance decrease. However, the bonding strength between solid atoms and the solid atomic mass influence the interfacial resistance remarkably while they have little effect on the contact angle. It is because the variations of the solid atomic mass and the bonding strength between solid atoms change the frequency distribution of the vibration of the solid atoms, resulting in a difference in the thermal vibrational coupling between solid and liquid atoms. Our study indicates that the interfacial thermal resistance is not only related to the interfacial solid-liquid bonding strength which is characterized by the contact angle, but also the thermal vibrational coupling between solid and liquid atoms. There is not a simple relationship between the contact angle and the interfacial thermal resistance. The contact angle could not be used as an exclusive criterion for solid-liquid interfacial resistance estimation.
2013, 62 (11): 110205. doi: 10.7498/aps.62.110205
By using the self-similar method to solve the nonlinear Schrödinger eguation with distributed coefficients, the self-similar solitons in Bessel lattice are studied under the hollow cylinder boundary conditions and the analytical solutions are obtained. Analytical solutions and numerical solutions are found to be identical. The result indicates that optical lattices induced by non-diffractive Bessel beams are possible to support stable self-similar soliton clusters.
2013, 62 (11): 110301. doi: 10.7498/aps.62.110301
The dynamical entanglement in a model of the field interacted with atoms in a nonlinear medium is studied in terms of concurrence and the reduced Neumann entropy for the generalized binomial state of the field and the ground state of atoms. It is shown that concurrence is dominantly-positively correlated with the reduced Neumann entropy. The entanglement under suitable condition is nearly unchanged for a long time. This is useful for quantum information processing.
In this paper, we have investigated the off-diagonal Berry phase of nonlinear systems and presented its explicit expression. The results show that, for nonlinear systems, the off-diagonal berry phase contains a new term in addition to the dynamical phase, the geometric phase and the nonlinear phase. This new term can describe a cross effect between the Bogoliubov excitation around one eigenstate and another instantaneous eigenstate, while the Bogoliubov excitations are found to be accumulated during the adiabatic evolution and contribute a finite phase of geometric nature. As an application, the off-diagonal Berry phase of a two-well trapped Bose-Einstein condensate system is calculated.
2013, 62 (11): 110303. doi: 10.7498/aps.62.110303
The quantum discord of a two-qubit one-dimonsional Heisenberg XXZ spinchain in thermal equilibrium depends on the temperature T, when subjected to different magnetic fields, with B1 and B2 acting separately on the qubit, is studied in this paper. Four cases are considered here: (1) B1=B2 = 0 (without magnetic field); (2) B1≠0,B2=0 (only one qubit in magnetic field); (3) B1=B2 (homogeneous magnetic field); (4) B1=-B2 (inhomogeneous magnetic field). The similarities and difference between quantum discord and quantum entanglement are calculated and discussed in detail. Results show that the quantum discord is more robust than quantum entanglement against temperature, and the effect of inhomogeneous magnetic field is preferable for the quantum communications and quantum information processing, as compared with the effect of homogeneous magnetic field.
2013, 62 (11): 110304. doi: 10.7498/aps.62.110304
Ultracold atoms trapped in an optical lattice of double-well potential, the so-called optical superlattice, have received much attention in the field of cold atoms. A protocol generalized to three-well optical superlattice is suggested in this paper. The ground-state diagrams of ultracold spin-1 atoms trapped in a symmetric three-well optical superlattice in a weak magnetic field are studied based on the exact diagonalization. It is shown that the ground-state diagrams are remarkably different for the ferromagnetic and antiferromagnetic atoms. There does not exist the type of ground state for the antiferromagnetic interaction atoms, where the magnetic quantum number of the total spin of the system along the external magnetic field are ±2. But for the ferromagnetic interaction atoms, there do exist. In addition, there exist only the fully polarized ground-states for the ferromagnetic atoms in the negative quadratic-Zeeman-energy region. The physicsal origin of the dependence of the ground states on the controllable parameters are analyzed. These quantum spin-states can be controlled easily and exactly by modulating the external magnetic field and the height of the optical barrier, which may be a tool for the study of spin-entanglement.
2013, 62 (11): 110305. doi: 10.7498/aps.62.110305
In this paper we study the nonlinear Landau-Zener tunneling of a boson-fermion mixture in a double-well potential by adjusting the interaction parameter of its components. We find that the tunneling in the system can be affected by adjusting the interatomic self-interaction parameter. Moreover, we notice that the tunneling in the system show a critical phenomenon if variation of interatomic self-interaction, and critical point are given.
2013, 62 (11): 110501. doi: 10.7498/aps.62.110501
Using multiple-scale method, we study analytically the soliton dynamical behaviors of the Bose-Einstein condensates trapped in a square-well potential. It is found that the square-well potential has important effects on the soliton dynamics. When the soliton goes into the square-well potential, its movement is accelerated; while it leaves the square-well potential, the soliton is decelerated. With the increase in depth of the square-well potential, the velocity of the soliton increases, and its amplitude becomes larger and its width decreases. This may serve as a reference effect for controlling the dynamical characteristics of the soliton in experiments.
Effects of non-Gaussian noise on negative mobility in an inertial ratchet were investigated by means of stochastic simulation method. The absolute negative mobility (ANM), negative nonlinear mobility (NDM), and negative differential mobility (NNM) were simulated, separately. Results indicate that: (i) non-Gaussian noise can either enhance or diminish the phenomena of ANM, and non- Gaussian noise also can induce NDM and NNM in regions of parameter space. (ii) The average velocity-correlation time characteristics shift towards small value of correlation time. (iii) The absolute value of negative-valued minima decreases as the non-Gaussian noise parameter q increases.
2013, 62 (11): 110503. doi: 10.7498/aps.62.110503
After dimension reduction, two boundary voltages of V2 controlled buck converter are deduced under different operation mode, based on which, its equivalent one-dimensional discrete-time model is established and complex nonlinear bifurcation behaviors are emphatically studied. Two boundary conditions under which shift between stable period-one state and subharmonic oscillation state and shift between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) take place are derived by analyzing stability and operation mode. The research results show that in V2 controlled buck converter period-doubling bifurcation and border-collision bifurcation can occur with varying circuit parameters and the converter has different bifurcation routes at different circuit parameters. Simulation and experiment platforms are implemented and the corresponding results verify the validity of equivalent discrete-time model and theoretical analysis.
Study on nonlinear phenomena in single phase H bridge inverter based on the periodic spread spectrum
2013, 62 (11): 110504. doi: 10.7498/aps.62.110504
The periodic spread spectrum technologies used in converter to suppress its electromagnetic interference and noise have been applied widely, while the nonlinear phenomenon is ignored. Based on the analysis of the periodic spread spectrum technology and single-phase H bridge converter accurate stroboscopic map model, the bifurcation and chaos phenomenon of the single-phase H bridge circuit is studied and the discrete model of the H bridge sine inverter is established by means of periodic spread spectrum technology. The nonlinear phenomenon is analyzed using the time domain chart, folding map, bifurcation diagram and Lyapunov index spectrum. Results show that the H bridge sine inverter based on the spread spectrum technology can go into the chaotic region more easily when it is in the nonlinear region, and it is concluded that the frequency of cycle spread spectrum has important effect on the initial branch point position of system.
2013, 62 (11): 110505. doi: 10.7498/aps.62.110505
In this paper, we propose an improved CSR model for rumor spreading in mobile social networks. The dynamic equation of rumor spreading is modified to be suitable for user's habit in mobile social networks. In the acceptant probability model, negative and positive social reinforcements are considered. Furthermore, the people's accepting threshold for rumor accepting is taken into account. Analytically, a mean field theory is worked out by considering the influence of network topological structure as homogeneous. Under certain conditions, rumor spreads faster and wider in the new model than CSR rumor spreading model in homogeneous networks. Meanwhile, the multi-agent simulation results indicate that the information spreading process is sensitively dependent on initial conditions.
2013, 62 (11): 110506. doi: 10.7498/aps.62.110506
In this paper, the local maximum of joint entroy was computed using the symbolic analysis method so as to determine the appropriate delay time of the phase space reconstruction. The numerical experiments for three typical chaotic systems show that the present method could reduce computation, increase the efficiency, and also could obtain the optimum delay time accurately and rapidly. And it could reconstruct the original phase space from the time series effectively. Thus it provides a fast and effective way to identify the chaotic signal.
2013, 62 (11): 110507. doi: 10.7498/aps.62.110507
We optimize and design a new half-ring conductance sensor for measuring two-phase flow in a small diameter pipe. Based on the experimental signals measured from the designed sensor, we using the limited penetrable visibility graph we proposed construct complex networks for different flow patterns. Through analyzing the constructed networks, we find that the joint distribution of the allometric scaling exponent and the average degree of the network allows distinguishing different gas-liquid flow patterns in a small diameter pipe. The curve peak of the degree distribution allows uncovering the detailed features of the flow structure associated with the size of gas bubbles, the average degree of the network can reflect the macroscopic property of the flow behavior, The allometric scaling exponent is very sensitive to the complexity of fluid dynamics and allows characterizing the dynamic behaviors in the evolution of different flow patterns. In this regard, limited penetrable visibility graph analysis of fluid signals can provide a new perspective and a novel tool for uncovering the dynamical mechanisms governing the formation and evolution of different flow patterns.
Hardware implementation for blind demodulation method for chaotic direct sequence spreadspectrum signals
2013, 62 (11): 110508. doi: 10.7498/aps.62.110508
In this paper, we design a field-programmable gate array (FPGA)-based hardware implementation for blind demodulation method for chaotic direct sequence spread spectrum (CD3S) signals. Both transmitter and receiver are designed. The transmitter can produce ten chaotic maps as the spreading sequence. In the receiver, the mathematic model of unscented Kalman filter (UKF) chaotic fitting is built and simplified for hardware implementation. The hardware structure of the receiver is based on this simplified model. For real time fitting different chaotic maps, a dynamic adjustment strategy of range-differentiating factor is proposed. The additove white Gausian noise (AWGN) and multipath channel experiments verify the anti-noise and anti-multipath performance of the UKF chaotic fitting method on one hand. On the other hand, the experiments verify the method can demodulate CD3S signals spread by all ten chaotic maps effectively.
2013, 62 (11): 110509. doi: 10.7498/aps.62.110509
To solve the problem of indeterminate synchronization time in different chaotic systems, this paper presents a time-controllable synchronization scheme. A general synchronization controller and parameter update laws are proposed to stabilize the error system, thus the drive and response systems could be synchronized up to a given scaling matrix at a pre-specified exponential convergence rate. The synchronization time formula is strictly deduced, which suggests that the speed of synchronization is determined by several parameters, such as exponential rate, initial system value and other parameters brought in by the controller. By adjusting these parameters, the performance of the synchronization can be effectively improved. In numerical simulation, two nonidentical 3D autonomous chaotic systems are chosen to verify this method. The error system can be rapidly stabilized, and unknown parameters are also identi?ed correctly. Firally, two groups of time-controllable parameters are given to verify the theory, wherein synchronization of both cases can be obtained quickly and each result of the synchronization is consistent with the theoretical calculation. The synchronization scheme is characterized by high safety and efficiency, and has its potential value in secure communication.
Complicated behaviors and non-smooth bifurcation of a switching system with piecewise linearchaotic circuit
2013, 62 (11): 110510. doi: 10.7498/aps.62.110510
The complex dynamical and non-smooth bifurcations of a compound system with periodic switches between two piecewise linear chaotic circuits are investigated. Based on the analysis of equilibrium states, the conditions for Fold bifurcation and Hopf bifurcation are derived to explore the bifurcations of the compound system with periodic switches while there are different stable solutions in the two subsystems. Different types of oscillations of the swithing system are observed, and the mechanism is studied and presented. In the difference of periodic oscillations, the number of the swithing points increases doubly with the variation of the parameter, which leads from period-doubling bifurcation to chaos.
2013, 62 (11): 110701. doi: 10.7498/aps.62.110701
A novel joint compression-encryption algorithm based on embedded zerotree wavelet (EZW) coding is proposed. Encryption process is performed before entropy coding. The principles of the context modification and the decision modification and described. Simulation results show that the proposed algorithm has a good effect on security, and has the same compression efficiency compared to the original image compression algorithm.
The numerical-aperture-dependent optical contrast and thickness determination of ultrathin flakes of two-dimensional atomic crystals: A case of graphene multilayers
2013, 62 (11): 110702. doi: 10.7498/aps.62.110702
The optical and electronic properties of two-dimensional atomic crystals including graphene are closely dependent on their layer numbers (or thickness). It is a fundamental issue to fast and accurately identify the layer number of multilayer flakes of two-dimensional atomic crystals before further research and application in optoelectronics. In this paper, we discuss in detail the application of transfer matrix method to simulate the optical contrast of ultrathin flakes of two-dimensional atomic crystals and further to identify their thickness, where numerical aperture of microscope objective is considered. The importance of numerical aperture in the thickness determination is confirmed by the experiments on the graphene flakes. Furthermore, two lasers with different wavelengths can be serviced as light sources for the thickness identification of flakes of two-dimensional atomic crystals with a size close to the diffraction limit of the microscope objective. The transfer matrix method is found to be very useful for the optical-contrast calculation and thickness determination of flakes of two-dimensional atomic crystals on multilayer dielectric substrate.
Numerical simulation of electrode potential influence on the performance of ionization gauge with carbon nanotubes cathode
2013, 62 (11): 110703. doi: 10.7498/aps.62.110703
Theoretical studies of electrodes potential influence on the sensitivity and ratio of anode current and emission current (Igrid/Ie) will be beneficial for providing theoretical basis and experimental instruction in the research of ionization gauge with carbon nanotubes cathode. In this paper, based on the structure of IE514 extractor gauge, the model of carbon nanotube ionization gauge is built by ion optic simulation software SIMION 8.0. And the influence of electrode potential on the sensitivity and Igrid/Ie is discussed. Results show that with increasing ratio between anode voltage and gate voltage (Vgrid/Vgate), Igrid/Ie increases, while the sensitivity of the gauge decreases with the increase in anode voltage, which would further affect the extension of vacuum measurement lower limit. Moreover, the simulation results are in good agreement with the experimental data reported. Consequently, it is very important to improve the sensitivity, anode current and extension of measurement lower limit to set up an appropriate electrode voltage. In addition, the method adopted in this paper can be extended to the research and development of new-styles of extremely high vacuum ionization gauge of carbon nanotube cathode, which could provide an effective method to resolve the problem of extremely high vacuum measurement.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2013, 62 (11): 111301. doi: 10.7498/aps.62.111301
In order to break the limitation of gyrotron emission producing the ideal electron beam in the traditional gyrotron numerical simulation, this paper on the basis of theoretical analysis of structural parameters for the 94 GHz double-anode magnetron injection electron gun, by optimizing the grid plot of conformal FDTD algorithm, obtains the high-performance electron beam of the horizontal and vertical velocity ratio of 1.42 and the maximum velocity spread of 5.92%, By using the optimized electron gun to replace the traditional gy rotron emission in the numerical simulation of the gyrotron system and using the four-process parallel MPI in computation, we finally obtain a TE03 mode, 94 GHz, the average output power of about 40 kW, with on efficiency of 10.5% for the high-performance gyrotron oscillating tube.
2013, 62 (11): 112901. doi: 10.7498/aps.62.112901
The gamma-ray spectrum analysis is an important method for quantitative analysis of radionuclide. Although widely used, the weak peak identification and overlapping peaks resolution are still difficult for gamma-ray spectrum analysis. To solve the problem, a new method based on compressed sensing is proposed for improving gamma-ray spectrum analysis in this paper. The proposed method models physical modulation of gamma spectrometer as a linear equation, and formulates the gamma-ray spectrum analysis as a corresponding inverse problem. The true gamma spectrum is obtained by solving the inverse problem by applying sparsity constraint under the framework of compressed sensing. The feasibility of the proposed method is demonstrated by both numerical simulation and Monte Carlo simulation experiments. Results demonstrate that the proposed method can simultaneously resolve overlapped peaks and reduce the fluctuations of gamma-ray spectrum, effectively improving the accuracy of gamma-ray spectrum analysis.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (11): 113101. doi: 10.7498/aps.62.113101
The potential energy curves (PECs) of X4∑- and B4∑- states of the AlC molecule have been studied using highly accurate internally contracted multireference configuration interaction approach with the Davidson modification. The Dunning's correlation-consistent basis sets, aug-cc-pVnZ (n=D,T,Q,5,6) are used for the present study. To improve the quality of PECs, core-valence correlation and scalar relativistic corrections are considered. Core-valence correlation corrections are calculated with an aug-cc- pCVTZ basis set. Scalar relativistic correction calcualtions are made using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. Obvious effect on the PECs by the core-valence correlation and relativistic corrections has been observed. All the PECs are extrapolated to the complete basis set limit. The convergence observations of present calculations are made and the convergent behavior is discussed with respect to the basis set. Using these PECs, the spectroscopic parameters (TeReωeωexeωeyeBe and αe) of the X4∑- and B4∑- states are determined and compared with those reported in the literature. The vibration manifolds are evaluated for each state of non-rotation AlC molecule by numerically solving the radial Schrödinger equation of nuclear motion. For each vibrational state, the vibrational level and inertial rotation constants are obtained, which are in excellent accordance with the experimental findings.
2013, 62 (11): 113102. doi: 10.7498/aps.62.113102
The molecular structure of the ground electronic state (X3∑-) of SN- molecular ion has been calculated by using the CCSD(T) method in combination with the correlation-consistent basis sets aug-cc-pVXZ (X=D,T,Q,5). The equilibrium internuclear distance Re , harmonic frequency ωe and dissociation energy De of the molecular ion are derived and are extrapolated to the complete basis set limit. Comparisons of corresponding parameters between this work and those reported previously indicate our results agree well with the experimental data. A reliable potential energy curve is obtained and is perfectly reproduced in the form of the Murrell-Sorbie analytical potential function. we utilized have the potential energy curve to calculate the relevant spectroscopic parameters of the ground state of the system. The vibrational levels and corresponding molecular constants for the X3∑- state are obtained by solving the radial Schrödinger equation of the nuclear motion. Calculations in the present work indicate that an improvement in theoretical computations of SN- molecular ion is achieved.
Study on spectroscopic properties and molecular constants of the ground and excited states of AsCl free-radical
2013, 62 (11): 113103. doi: 10.7498/aps.62.113103
The dissociation limit of AsCl free-radical is correctly determined based on group theory and atomic and molecular statics. Potential energy curves (PECs) for the ground state and several low-lying electronic excited states of AsCl free-radical are calculated using the multi-reference configuration interaction method with the basis set of aug-cc-pV5Z where the Davidson correction is considered as an approximation to full CI. Separation parameters (Re, e, ee, D0, De, Be and e) are evaluated using the PEC of AsCl. Spectroscopic parameters are compared with those reported in the literature, and excellent agreement is found between them. With the PEC of AsCl free-radical, forty vibrational states of AsCl free-radical are predicted when J=0 by numerically solving the radial Schrdinger equation of nuclear notion. For each vibrational state, the vibrational levels and inertial rotation constants are reported.
2013, 62 (11): 113201. doi: 10.7498/aps.62.113201
Solving numerically the time-dependent Schrödinger equation in three-dimensional momentum space, we have investigated the energy spectroscopy and two-dimensional momentum angular distribution near the ionization threshold of the photoelectron generated from excited atom under the action of high-frequency laser pulse. The results show that the ionized process is mainly the single-photon ionization in this energy range. The principal quantum number of the initial state can be determined by the position of the first peak in photoelectron spectrum; its angular quantum number of the initial state can be determined by the angular distribution of the two-dimensional momentum of the photoelectron. This law does not change with the variation of the intensity and pulse duration of the incident laser pulse within a relatively broad range of these parameters. In principle, we can utilize these spectra to identify the initial state of the atoms. In addition, the photoelectron momentum spectrum of superposition state is investigated for different relative phase of the state.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (11): 114101. doi: 10.7498/aps.62.114101
With an existing metal wire array structure, this paper verifies the temporal and spatial focusing properties of the time reversal techniques, and confirms the super-resolution focusing properties of the time reversal electromagnetic waves. Since the metal wire array can provide an evanescent-wave channel, by changing the signal incentives to the time reversal mirror (TRM), this paper achieves some satisfactory simulation results of subwavelength off-site imaging. The analysis and simulation results indicate that with time reversal technique, we can use traditional materials and equipment to achieve super-resolution confocal imaging in the far field, and extract and analyze the source signal at different positions.
Shielding effectiveness of an apertured rectangular cavity against the near-field electromagnetic waves
2013, 62 (11): 114102. doi: 10.7498/aps.62.114102
The shielding effectiveness of an apertured rectangular cavity against the near-field waves of both electric and magnetic dipoles is investigated theoretically by using an extended equivalent circuit method. Both electric and magnetic shielding effectivenesses are calculated as functions of distance between the dipoles and the enclosure. It is shown that the near-field shielding effectiveness is lower than the far-field (plane-wave) shielding effectiveness. Also, in the near-field region, the shielding effectiveness will reduce obviously with the decrease of the source-to-enclosure distance. Based on Bethe's small aperture coupling theory, analytical formulas are presented to describe the quantitative relation between the near-field and the far-field shielding effectivenesses. It is shown that the results from equivalent circuit method are in good agreement with the relation obtained from the Bethe's theory.
2013, 62 (11): 114103. doi: 10.7498/aps.62.114103
During propagating through an underdense plasma, a laser will experience significant energy loss and will be trapped in the plasma as the frequency undergoing a redshift. Thus the electromagnetic (EM) soliton is formed. EM field distribution at different stage is constructed for the soliton in terms of primary theory and particle in cell (PIC) simulation. Radiography of solitons produced by laser accelerated MeV protons is investigated using Monte Carlo methods. The influencing fact or such as proton energy and source size is analyzed. Time-resolved radiography of the soliton is also carried out as the protons accelerated by the target normal sheath acceleration (TNSA) mechanism have a wide energy spectrum. Results validate the static electric field model of the soliton, and provide the basis for the future experiments.
2013, 62 (11): 114201. doi: 10.7498/aps.62.114201
The scattering features of a spheroidal particle illuminated by the Laguerre- Gaussian (LG) beam have been studied based on the generalized Lorenz-Mie theory. By using the localized approximations method, the beam shape coefficients are evaluated and the results obtained agree with the cases of on-axis incidence. Calculations of the far-field scattering intensity are performed to study the LG beam scattered by spheroids, of different size parameters and eccentricities. The simulation results show that when the particle's size parameter is within the range that can be compared to the wavelength of the incident light, the magnitude of the scattering intensity will increase as the particle's size parameter increases, and it will decrease as the ratio of the spheroid's major axis to minor axis increases. Comparisons between LG beams with different topological charges illumination are made and explained physically. It turns out that the magnitude of the scattering intensity decreases as the topological charge increases. The theoretical investigation in this paper may provide a more accurate particle model and reference for applications of LG beams in areas such as particle size measurement, atmospheric laser communication, atmospheric remote sensing and so on.
2013, 62 (11): 114202. doi: 10.7498/aps.62.114202
Despite the advances made in areas such as DNA profiling, fingerprints are still considered to be the best form of personal identification for criminal investigation purposes. A variety of physical chemical and optical techniques are available for the enhancement and detection of latent fingerprints. However, existing frequently-used fingerprint detection methods show some disadvantages such as harm to fingerprints, slow extraction, potential side effects, leaving trails, high contrast demand and so on. A new method based on phase sensitive spectral domain optical coherence tomography (SD-OCT) for latent fingerprints detection is proposed. This method has advantages of non-contact non-destructive, high-speed and high-sensitivity. The experimentel results demonstrate that using this method to deal with fingerprints of low contrast also leads to satisfactory results, proving that the sensitivity of SD-OCT can be used for accurate and reliable patent fingerprint recognition.
2013, 62 (11): 114203. doi: 10.7498/aps.62.114203
For designing the light beam shaper in the optical transmitting antenna in inter-satellite optical communication system, the essential problem is, according to the input optical field and ideal output light field, to determine the shaper of phase distribution, in which its core is in phase recovery. Based on the traditional Gerchberg-Saxton (G-S) iterative algorithm, using the angular spectrum propagation theory, a kind of amplitude gradient addition iterative algorithm is proposed, and the detailed algorithm process and analysis are given. Compared with G-S algorithm, the new one using iterative process, constructs the light field amplitude feedback loop, and searches out the optimal iteration path using the gradient; their joint action accelerates the convergence process. Numerical simulation shows that the iterative error-drop speed caused by unit iterations in the new algorithm is 1.7 times that of the G-S algorithm, its convergence rate is obviously superior to the G-S algorithm; for different random initial phase, the new algorithm can effectively carry out iteration, show the advantages of the strong adaptability and the good convergent consistency. Amplitude gradient addition iterative algorithm gives a new effective way of recovering the complex optical field phase, and provides technical support for designing all kinds of diffraction optical element.
2013, 62 (11): 114204. doi: 10.7498/aps.62.114204
Using the formula of Wigner function in coherent representation, we have obtained the analytical expression for Wigner function of N00N state. Based on phase space method, we study the quantum interference with N00N state as input. We derive the analytical expression of conditional probability related with the input parameter N and phase parameter φ and analyze it numerically. It is shown that, when φ is 0 or π, the output is just N00N state. It is also shown that, for 2002 state as input, the output must be 2002 state, which is independent of phase parameters. Moreover, as the number of input photon N increases, the phase probability distributions remain to have one, two, three and four peaks and get narrower. All these results can offer theoretical reference for experiments.
Spin coherent-state transformation and analytical solutions of ground-state based on variational-method for spin-Bose models
2013, 62 (11): 114205. doi: 10.7498/aps.62.114205
We present a variational method for the ground-state solutions of the spin-Bose models by means of the spin coherent-state transformation. For the Jaynes-Cummings (J-C) models with and without the rotating-wave approximation, the ground-state energies obtained by this method are in perfect agreement with the results from numerical diagonalization in the whole region of the coupling between a light field and an atom. The present variational-method can be directly used to solve the ground-state energies of the Dicke models with arbitrary atom-numbers and furoher study the quantum phase transition; while the variational-method based on the Holstein-Primakoff transformation is only valid in principle for the thermodynamic limit with the atom-number tending to infinity.
2013, 62 (11): 114206. doi: 10.7498/aps.62.114206
In a Yb3+ laser, the two-energy level structure is close to the quasi-three-level model, but different from that for the Nd and Tm lasers, so it is necessary to investigate the quasi-three-level modeling that will be applied to the Yb3+ laser. Based on the energy level structure, cavity gain and loss as well as population distribution, we present the modeling. Introducing an effective cavity length factor, the laser intensity is calculated and the threshold is obtained. Comparison with the experiments, indicates that the effective cavity length ratio changes the fractional population function and loss, which would influence the threshold and output in turn. Applied to investigate the laser property in the process of end pumping Yb3+:YVO4 laser, we get the threshold being 1.1 W, corresponding to the L=1 mm and T=1%; whereas the threshold is 3.9 W, corresponding to the L=2 mm and T=10%.
2013, 62 (11): 114207. doi: 10.7498/aps.62.114207
Hollow and solid cylindrical opals and inverse opals have been made by the self-assembly method in a capillary. The mechanism as well as the assembly process of monodispersed microspheres self-assembly in a capillary has been investigated. By the vertical self-assembly method, hollow cylindrical polystyrene opals and silica inverse opals of different radii have been made in capillaries; whereas cylindrical solid opals and inverse opals have been prepared under the interactions of gravity sedimentation, evaporation induced micro-flow, liquid surface tension and capillary tension. The growth process of producing solid photonic crystals in capillaries have been described and discussed. By scanning electron microscope, we characterize the internal structure of the samples and with spectrometer we test the reflection spectra of these films. Results show that the substrate curvature radius and microsphere size are the main factors that affect the quality of hollow cylindrical opal and inverse opal films while microsphere size has influence on the internal structure of solid cylindrical opals and inverse opals.
2013, 62 (11): 114208. doi: 10.7498/aps.62.114208
We present a novel GeSi electro-absorption (EA) modulator design on a silicon-on-insulator platform. The GeSi EA modulator is constructed based on the Franz-Keldysh (FK) effect. The light is evanescent-coupled into the GeSi absorption layer from the rib Si waveguide. A contnet of 1.19% Si in SiGe absorption layer is chosen for C (1528–1560 nm) band operation. Simulation shows a high (3 dB) bandwidth of ～ 64 GHz and extinction ratio of 8.8 dB. Especially the insertion loss is as low as 2.7 dB.
A combined scheme of polarization mode dispersion compensation and polarization de-multiplexing in a polarization division multiplexing system with direct detection
2013, 62 (11): 114209. doi: 10.7498/aps.62.114209
A model of polarization mode dispersion (PMD) and state of polarization (SOP) variation induced coherent crosstalk is established in a polarization division multiplexing system. The properties of radio frequency power of one channel in the presence of PMD are investigated. A combined scheme of PMD compensation and polarization de-multiplexing in optical domain is proposed, which is based on monitoring of the feedback signal of RF power. A modified particle swarm optimization algorithm is also used for the adaptive polarization control. The validity of the PMD compensation and polarization de-multiplexing scheme proposed here is demonstrated in a 112Gb/s-PDM-DQPSK simulation system. Results show that the PMD tolerance of the transmission system is increased by 20 ps with 1 dB OSNR margin and the channel separation is accomplished as well.
2013, 62 (11): 114301. doi: 10.7498/aps.62.114301
The wall of elastic microtubules can be described as a membrane-type elastic structure. An oscillating system driven by ultrasound consists of liquid columns, a bubble and elastic wall of the tube. The nonlinear properties of this system are explored. Based on the successive approximation method, the nonlinear resonance frequencies, the amplitude response of fundamental and third oscillations to driving acoustic wave, and the mechanism of resonance response related to the driving wave whose frequency is lower than the resonant frequency are analyzed theoretically. The nonlinear system is oscillating in two directions: the axial and radial directions of the bubble in the microtubule. Numerical results show that the resonance responses cannot be present simultaneously. It has been found that the amplitudes of the fundamental and third harmonic oscillation are multivalued, which may lead to instable response. The third harmonic oscillation is stronger in the region of lower frequencies.
2013, 62 (11): 114501. doi: 10.7498/aps.62.114501
Granular materials consist of a large number of discrete solid particles. When subjected to external vibrations, they exhibit various intricate dynamical behaviors, Which usually depend in a complicated way on many physical factors, such as air dragging, friction from the container wall and so forth. In this work, vertical vibrations are applied to a bed of stainless-steel spheres contained in a glass tube, and the subharmonic bifurcations of impact of particles on the container bottom are investigated. To eliminate the effects of air dragging, we evacuate the container or perforate the container bottom to make it quite permeable to the air. Experiments performed in such containers reveal that the impact bifurcations are controlled solely by the normalized vibration acceleration, but independent of the particle size, the filling height of particles, and the frequency of forced vibration. The sliding friction from the container wall is treated as a constant one with the direction opposite to the velocity relative to the container wall. By involving this damping term into the completely inelastic bouncing ball model, an explanation for the experimental results is made. Simulations on the averaged experimental bifurcation points indicate that the magnitude of wall friction is about 10% of the total weight of the particles.
Numerical investigation on the characteristics of the mushroom-like vortex structure generated by a submerged laminar round jet
2013, 62 (11): 114701. doi: 10.7498/aps.62.114701
A numerical investigation on the evolution mechanism and characteristics of the submerged laminar round jet in a viscous homogenous fluid is conducted by using the computational fluid dynamics method based on the incompressible Navier-Stokes equation. Three non-dimensional parameters for the mushroom-like vortex structure, including the length of the jet L*, the radius of the mushroom-like vortex R* and the length of vortex circulation d*, are introduced and the variation characteristics of these parameters with the non-dimensional time t* are quantitatively analyzed. Results show that there exist three distinct stages in the formation and evolution procedures of the mushroom-like vortex structure, including the starting, developing and decaying stages. In the starting stage, L* and d* increase linearly with t*, while R* approximately remains to be a constant; in the developing stage, a considerable self-similarity is confirmed, and L*, R*, d* display the same proportional relationship to t*1/2 regardless of the variations of Reynolds number and injection duration; in the decaying stage, L* and R*are approximately proportional to t*1/5, while d* nearly levels off as a constant. Moreover, velocity characteristics at the secondary backflow point and the momentum and geometry centers, the distribution features of the vertical vorticity, as well as the vorticity-stream function relationship are analyzed for the mushroom-like vortex structure.
2013, 62 (11): 114702. doi: 10.7498/aps.62.114702
Based on the compressible fluid theory, the boundary integral equation is used to solve the motion law of cavitation in vortex flow within different surface pressure models. The time-domain sound pressure characteristics induced by cavitation in vortex field are obtained by the moving surface Kirchhoff formulation. With the surface discretion and coordinate transformation, the cavitation surfaces are treated as the moving deformable boundary and the acoustic source directly. The influence of vortex field parameters on motion and radiation of cavitation is analyzed. Results show that with the consideration of compression, the amplitude of cavitation's pulsation as well as the sound pressure will be decreased. In the vortex fluid, cavitation will be extended, necked and splitted, and may generate a jet in sub-bubbles. While the pressure is reduced in the fluid field, the maximum radius and length before splitting of the cavitation will be enlarged. The number of sub-bubbles will increase when the pressure is small in the fluid field. The directive property of cavitation is weak. And the splitting of cavitation will generate a great peak value of sound pressure. With the increase in vortex flux or the decrease in the cavity number, the period of the cavitation oscillation and its radiation sound pressure are elongated, and the peak of sound pressure is retarded and reduced. The results in this paper could be used as the reference data for the research about the motion and sound radiation characteristics of cavitation in vortex fluid.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (11): 115201. doi: 10.7498/aps.62.115201
An improved multi-component two-dimensional hybrid model is presented for the simulation of Trichel pulse corona discharge. The model is based on the plasma hydrodynamics and chemical models, including 12 species and 27 reactions. In addition, the photoionization and secondary electron emission effects are taken into account. Simulation is carried out on a bar-plate electrode configuration with an inter-electrode gap of 3.3 mm, the positive potential applied to the bar being 5.0 kV, the pressure in air discharge being fixed at 1.0 atm, and the gas temperature assumed to be a constant (300 K). In this paper, some key microscopic characteristics such as electric field distribution, net charge density distribution, electron density distribution at 5 different instants during a Trichel pulse are analyzed emphatically. Further more, the electron generation and disappearing rates, positive and negative ion distribution characteristics along the axis of symmetry are also investigated in detail in the later Trichel pulse cycle. The results can give valuable insights into the physical mechanism of negative corona discharge.
2013, 62 (11): 115202. doi: 10.7498/aps.62.115202
Investigation of electronegative plasmas has now been atrractive due to the advantages of negative-ion assisted etching and charge-free ion implantation in semiconductor manufacture. Langmuir electrostatic probe, as a simple, inexpensive and good spatial resolution diagnosic tool, is popularly used in investigating electronegative plasmas. In this paper, the Langmuir electrostatic probe is proposed to measure the capacitively coupled Ar plasmas with added electronegative gases, such as O2, Cl2 and SF6. The experimental results from the measurements of Ar plasmas with added electronegative gases driven by a 40.68 MHz field indicate that, with increasing flow rate of electronegative gas, high energy peak will occur in electron energy possibility function and shift towards higher energyside. The addition of electronegative gases reduces the electron density significantly as the electron temperature increases. We also calculate the electronegativity of Ar plasmas for the three kinds of electronegative gases. The preliminary interpretations of the above experimental phenomena are presented.
Simulation of hollow cathode discharge by combining the fluid model with a transport model for metastable Ar atoms
2013, 62 (11): 115203. doi: 10.7498/aps.62.115203
The characteristics of rectangular hollow cathode discharge are studied based on a fluid model combined with a transport model for metastable Ar atoms in argon. The distribution of potential, density of electrons and ions, and the density of metastable atoms are calculated at a pressure of 10 Torr. The peak density of electron and ion is 4.7×1012 cm-3, and the peak density of metastable atoms is 2.1×1013 cm-3. Results obtained in terms of fluid-metastable hybrid model are compared with that in terms of the fluid model, which show that the electron produced by stepwise ionization is one of the important source of new electrons, and the metastable atoms have an obvious effect on the hollow cathode discharge. Compared with the results calculated in terms of fluid model, the density of electrons obtained in terms of hybrid model increases, and the depth of cathode sheath and the averaged electron energy decrease.
Coupled mode theory is an effective tool for analysis and synthesis of overmoded waveguides, but the inverse problem has not been solved yet. This paper completed the iterative procedure to solve the inverse problem. The new method can design automatically and fast various mode converters, mode transducers and horn antennas with special radial pattern. Compared with conventional methods, the structure design using the new method has more advantages in electromagnetic and structural properties. Two design examples are given: dual band TM01-TE11 mode converter and smooth-wall feed horn antenna. The two working frequencies of the dual band TM01-TE11 mode converter are 8.75 GHz and 10.3 GHz, and the radius is 16 mm. The converter efficiencies exceed 99% at the two working frequencies. The smooth-wall feed horn antenna converts the TE11 mode to Gaussian beam effectively. Simulation results agree well with the theoretical predictions.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (11): 116101. doi: 10.7498/aps.62.116101
In the present paper, function test of different test pattern was used to investigate function failure of static random access memory (SRAM) induced by the total dose effect. By comparing the function test results of different test pattern and single error bit, it is shown that the failure mode of the device is data retention fault, and different storage cell had diverse data retention time, the fault module of device is the storage cell. We discussed the reason for these phenomena in detail using simple circuit model of storage cell, and also analyzed the influence of these phenomena on test method to evaluate the total dose radiation damage of SRAM.
2013, 62 (11): 116201. doi: 10.7498/aps.62.116201
The elastic properties of hexagonal phase ErAx (A=H, He) have been calculated by the first-principles method, where x=0, 0.0313, 0.125, 0.25. Effects of different concentrations of hydrogen and helium on the elastic properties of ErAx systems have been investigated in detail. Results show that the elastic constants, Young's modulus, bulk modulus and shear modulus of ErHx systems increase mainly with increasing hydrogen concentration, whereas, those elastic properties of ErHex systems almost decrease with increasing helium concentration. We have investigated the changes in the charge densities of Er atoms produced by A atoms. It was found that the mechanism for the change of the elastic properties of hexagonal phase ErHx with increasing hydrogen atoms is different from that of ErHex with increasing helium atoms.
2013, 62 (11): 116202. doi: 10.7498/aps.62.116202
We have conducted experiments to study the melting fragments from explosively shocked melting Pb targets. Based on the traditional Asay-Window technique, Asay-F-window was designed, which is suitable to investigate high-density melting fragments of metal sample. The areal mass and volume density of melting fragments from the Pb target were presented, which is also compared with that of micro-jetting and solid spallation. The results may contribute to the understanding of physical mechanism and construction of dynamic model for melting fragments. Additionally, the Asay-F-Window technique is an effective supply for proton photography technique to study the dynamic fragmentation of melting metal.
2013, 62 (11): 116203. doi: 10.7498/aps.62.116203
When testing impact dynamics of concrete, usually a variety of kinetic effects can be seen, such as the axial and lateral inertial confinement effects, the effects of stress wave propagation and the final friction effects, etc. Some of these are the material is nature itself such as the size effect, some are experimental errors, etc., but all the dynamic effects, may enter the final test results so that unnecessary errors or even wrong values may be brought into experiments. Due to the mechanism of friction effect, we have designed three different sizes of specimen for SHPB test. The quantitative values of the friction effect are obtained. The DIF is corrected, which is the basis for concrete impact engineering design.
Effect of thickness on the properties of Cu(Inx,Ga1-x)Se2 back conduct Mo thin films prepared by DC sputtering
2013, 62 (11): 116801. doi: 10.7498/aps.62.116801
In this study, Mo thin films which used in Cu(Inx Ga1-x)Se2 (CIGS) thin film solar cells as back conduct were deposited on soda-lime glass substrates via DC magnetron sputtering under certain conditions. A series of Mo thin films prepared of various thicknesses was obtained in different sputtering deposition times. The microstructure, electrical resistivity and mechanical strain property of Mo thin films, which may be varied by controlling the thickness, were investigated by XRD, SEM, four probes technology and Scotch tape test. As the results showed, the thicknesses of the films increased linearly with the sputtering time. With increasing thickness, the films' crystal growth showed a change from (110) preferred orientation to (211) preferred orientation. The sheet resistance sharply reduced to 2 Ω/⇑ with the increase of (110) peak height and the resistivity linearly decreased to 0.96×10-4 Ω·cm due to the level of (110) preferred orientation. The films surface has porous (fish-like) grain morphology and intergranular voids. All the films are in a tensile state, and the inner strain decreased with the increase of the thickness.
2013, 62 (11): 116802. doi: 10.7498/aps.62.116802
Within the framework of effective-field theory with correlations, phase transition properties of ferroelectric thin films with different symmetrical surfaces described by the spin-1/2 transverse field Ising model are studied systematically by the differential operator technique. According to the coupling equations with the layer polarization average, the analytical general equations for phase diagrams of multiple-surface ferroelectric thin films with different surface layers have been derived. Then, effects of various parameter modifications on the crossover values from the FPD (ferroelectric-dominant phase diagram) to the PPD (paraelectric-dominant phase diagram) and phase transition regions in the parameter space are discussed in detail. In comparison with the mean-field approximation, the results indicate that the effective-field theory with correlations maybe reduce the ferroelectricity of the ferroelectric thin films more exaggeratedly than the mean-field approximation to some extent.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The site preference of refractory element W in NiAl dislocation core and its effects on bond characters
2013, 62 (11): 117101. doi: 10.7498/aps.62.117101
The site occupancy of refractory element W in the (010) edge dislocations of NiAl intermetallic compounds and its effect on NiAl properties are studied by the first-principles discrete variational method. The energetic parameters (binding energy, the impurity segregation energy and the interatomic energy), the density of states and the charge density are calculated respectively for the clean dislocation system and the doped dislocation system. The calculated results of the binding energy and the impurity segregation energy suggest that W exhibits a strong Al site preference. The interactions between the refractory elements W and the neighbouring host atoms are strengthened due mainly to the hybridization of 4d orbital of impurity atom and 3d orbital of host Ni atoms (3p orbital of host Al atom). Meanwhile, some charge accumulations appear between impurity atom and neighbouring host atoms in the dislocation core, indicating that strong bonding states are formed between the impurity atom and its neighbouring host atoms. The refractory element W greatly affects the energy and the electronic structure of NiAl intermetallic compounds, and in turn influences the motion of dislocation and the properties of NiAl compound.
2013, 62 (11): 117102. doi: 10.7498/aps.62.117102
The uniaxial tensile and compression tests of the Cu∑ 5 grain boundary (GB) with and without segregated interstitial boron have been performed using first principles method based on density functional theory. Results show that boron enhances the cohesion of Cu∑5 GB and improves the mechanical property of Cu significantly. The clean boundary has lower density of valence electrons than perfect lattices and will be the point for fracture to start under sufficiently high tensile stress. The Cu∑5 GB with segregated boron has strengthened the cohesion across the boundary because of the strong B-Cu bond. Charge accumulated to Cu-B decreases slightly the strength of neighboring Cu-Cu bonds, which will be the weak point for fracture to initiate. The ultimate tensile stress is enlarged by the addition of boron. There is no significant effects occurring within 20% of the compression strain due to B-doping.
2013, 62 (11): 117103. doi: 10.7498/aps.62.117103
Proton-irradiation-induced defects threaten seriously the stable performance of GaN-based devices in harsh environments, such as outer space. It is therefore urgent to understand the behaviors of proton-irradiation-induced defects for improving the radiation tolerance of GaN-based devices. Positron annihilation spectroscopy (PAS) has been used to study proton-induced defects in GaN grown by HVPE. The result shows that VGa is the main defects and no (VGaVN) or (VGaVN)2 is formed in 5 MeV proton-irradiated GaN. Photoluminescence (PL) spectrum is carried out at 10K. After irradiation, the band edge shows a blue-shift, but the donor-acceptor pair (DAP) emission band and its LO-phonon replicas is kept at the original position. The intensity of yellow luminescence (YL) band is decreased, which means that the origin of YL band has no relation with VGa. The increased FWHM of GaN (0002) peak in proton-irradiated GaN indicates a degradation of crystal quality.
2013, 62 (11): 117301. doi: 10.7498/aps.62.117301
Cu-CeO2 systems are widely used in solid oxide fuel cells and water gas shift reaction because of its special catalytic ability. The interfacial properties of the Cu/CeO2 (110) with the adsorption of Cu atom and Cu cluster are investigated in terms of first-principles based on density functional theory. It is found that: 1) the single Cu adatom prefers to be adsorbed on the oxygen bridge site; 2) the adsorbed tetrahedron structure of Cu4 cluster is the most stable cluster configuration on CeO2(110) surface; 3) the metal-introduced gap states in the gap area are mainly from the adsorbed Cu (cluster), its neighboring oxygcr and the reduced cerium ion(s), indicating that the activity of CeO2(110) surface is improved by copper adsorption; 4) the adsorbed Cu adatom and Cu4 cluster are oxidized to Cuδ+ and Cu4δ+ by their neighboring Ce ion(s) with the formation of Ce3+ ion(s), the reaction could be summarized as Cux/Ce4+→ Cuxδ+/Ce3+; 5) the adsorption of small clusters introduces more Ce3+ ions than a single Cu atom does, indicating that more Cuδ+-Ce3+ catalytic active centers are formed. The current study on Cu/CeO2(110) together with our previous results on Cu/CeO2(111) presents a good understanding of the synergies between Cu and ceria, and reveals the improvement of the activity of ceria by Cu adsorption.
2013, 62 (11): 117302. doi: 10.7498/aps.62.117302
The crystalline AlN thin film was fabricated on Si(100) substrates by plasma-enhanced atomic layer deposition. Its growth rate was illustrated by spectroscopic ellipsometer. And the surface morphology, crystal structure and composition were characterized by atomic force microscopy, X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Results show that the lowest temperature for deposition of the crystalline AlN thin film is 200 ℃, and the film coverage on the substrate surface is continuous and homogeneous. The film prepared with a homogeneous concentration distribution is polycrystalline with a hexagonal wurtzite structure. High resolution Al2p and N1s spectra confirm the presence of AlN with peaks located at 74.1 eV and 397.0 eV, respectively.
Effect of co-implantation of nitrogen and fluorine on the fixed positive charge density of the buried oxide layer in SIMOX SOI materials
2013, 62 (11): 117303. doi: 10.7498/aps.62.117303
Nitrogen ions implanted into the buried oxide layer can increase the total dose radiation hardness of silicon on insulator (SOI) materials. However, the obvious increase in positive charge density in the buried layer with high dose of nitrogen implantation leads to a negative effect on the technology of nitrogen implantation into buried oxide. In order to suppress the increase in positive charge density in the nitrogen-implanted buried layer, co-implantation of nitrogen and fluorine is used to implant fluorine into the nitrogen-implanted buried layer. High-frequency voltage-capacitance (C-V) technique is used to characterize the positive charge density in the buried layer. Results show that, in most cases, using the co-implantation of nitrogen and fluorine can significantly reduce the positive charge density in the nitrogen-implanted buried layer. At the same time, it is also found that further increase of the positive charge density induced by fluorine implantation in the nitrogen-implanted buried layer can occur in particular cases. It is proposed that the decrease in the positive charge density in the fluorine and nitrogen-implanted buried layer is due to the introduction of electron traps into the buried layer through fluorine implantation.
2013, 62 (11): 117304. doi: 10.7498/aps.62.117304
A theoretical simulation of electrical and optical characteristics of GaN-based dual-wavelength light-emitting diodes (LED) with high In content in the quantum dots (QDs) which are planted in quantum wells is conducted with APSYS software. The adjustment and contrast of the structure of the devices showed that the blue and green dual-wavelength LEDs will have a broader radiation spectrum and a higher color rendering index when QDs are planted in the green quantum wells. QDs have strong blinding capacity with the carriers, and the carriers at the QDs have shorter lifetime than they are in the wetting layers, so the carrier recombination will give preference to the QDs. It is shown that the distribution of the carriers could be easily controlled by adjusting the spacing layer thickness and the spacing layer doping concentration, so as to control the radiation rate of the two active layers of the dual-wavelength LEDs. Therefore, the spectrum-control of the dual-wavelength LED with QDs planted in QWs could be realized by adjusting the concentration of quantum dots, the thickness of the spacing layer and the doping concentration in the spacing layer. This article can provide guidance for the realization of the non-phosphor white LED.
Ultralow-voltage in-plane-gate indium-tin-oxide thin-film transistors made of P-doped SiO2 dielectrics
2013, 62 (11): 117305. doi: 10.7498/aps.62.117305
A new kind of indium-tin-oxide thin-film transistors made of P-doped SiO2 dielectrics in an in-plane-gate structure is fabricated at room temperature. Indium-tin-oxide (ITO) channel and ITO electrodes (gate, source, and drain) can be deposited simultaneously without precise photolithography and alignment process by using only one nickel shadow mask. So the thin film transistors (TFTs) have a lot of advantages, such as the simple device process、low cost etc. Such TFTs exhibit a good performance at an ultralow operation voltage of 1 V, a high field-effect mobility of 18.35 cm2/Vs , a small subthreshold swing of 82 mV/decade, and a large on-off ratio of 1.1×106, because of the huge electric-double-layer (EDL) capacitance (8 μF/cm2) between the interface of P-doped SiO2 dielectrics and ITO channel. So the TFTs are very promising for the application of low-power and portable electronic products and sensors in the future.
First-principles calculation of preferential site occupation of Dy ions in Nd2Fe14B lattice and its effect on local magnetic moments of Fe ions
2013, 62 (11): 117501. doi: 10.7498/aps.62.117501
The ground states of lattice properties, formation energy and magnetizations of R2Fe14B (R: rare-earth element) were calculated by the first-principles method based on the generalized gradient approximation (PAW-GGA). GGA+U method was applied to deal with local magnetic moments from 4f shell of rare-earth elements. Magnetic moments were calculated with and without spin-orbital interactions (SOI). Site occupation of Dy ions in Nd2Fe14B lattice is studied by partial substitution of Dy for Nd on different lattice sites. Calculated substitution energy indicates that the Dy2Fe14B is more stable than Nd2Fe14B and the Dy ions prefer to occupy the 4f sites in Nd2Fe14B lattice. It is also found that rare-earth ions occupying the 4f sites will interact more strongly with Fe ions and thus show a greater impact on the local magnetization of Fe. The interaction between rare-earth ions and Fe ions is positively correlated with distance.
Calculation and analysis of surface acoustic wave properties of ZnO film on diamond under different excitation conditions
2013, 62 (11): 117701. doi: 10.7498/aps.62.117701
In the last twenty years, the ZnO/diamond layered structure for surface acoustic wave (SAW) devices have been widely studied and have attracted great attention, due to its advantages of high acoustic velocity, high electromechanical coupling coefficient and high power durability. Distinguished from the conventional single-crystal substrate (such as quartz, lithium niobate), ZnO/diamond layered structure shows dispersive SAW properties, which can be excited by four ways: interdigital transducer (IDT)/ZnO/diamond, IDT/ZnO/shorting metal/diamond, ZnO/IDT/diamond, and shorting metal/ ZnO/IDT/diamond. In this paper, the formulation based on the stiffness matrix method for calculating the effective permittivity of ZnO/diamond layered structure under four excitation conditions is given first. Then, by using this formulation, the SAW properties of the monocrystalline ZnO (002) film on polycrystalline diamond and the polycrystalline ZnO (002) film on polycrystalline diamond are calculated respectively. Based on the results of calculation, the ZnO film thicknesses qualified to design and fabricate SAW device are analyzed in detail. Finally, we discuss the function of diamond film thickness of ZnO/diamond/Si layered structure so as to avoid the influence of the silicon substrate on the SAW properties.
2013, 62 (11): 117702. doi: 10.7498/aps.62.117702
The determinants of resonant frequency temperature coefficient (τf) have been analyzed by the approximate treatment of Clausius-Mossotti equation. It is suggested that the value of τf can be adjusted by changing the contribution proportion of ionic polarization or electronic polarization for the dielectric constant. Results of electronic structure calculation and tolerance factor analysis show that B-site substitution of CaTiO3 with (Zn1/3Nb2/3)4+ could turn the value of τf from positive to negative, by enhancing the covalency in the BO6 octahedron and improving the contribution proportion of electronic polarization. Ca[(Zn1/3Nb2/3)xTi(1-x)]O3 dielectric ceramics were prepared by solid-state reaction method with niobate as precursor. Results of structure analysis and property measurement conform to the theoretical analysis. The Ca[(Zn1/3Nb2/3)0.7Ti0.3]O3 dielectric ceramic with near-zero τf was obtained.
Effects of sefl-reduction of glass matrix on the broadband near infrared emissions from Bi-doped alkali earth aluminoborosilicate glasses
2013, 62 (11): 117801. doi: 10.7498/aps.62.117801
We report the effects of self-reduction of glass matrix on the broadband near infrared (NIR) emissions from Bi-doped alkali earth aluminoborosilicate glasses. Bi2O3 -doped as well as Eu2O3, -doped as a comparison, 35SiO2-25AlPO4-12.5Al2O3-12.5B2O3-15RO (R=Ca,Sr,Ba) glasses were prepared in air. Results show that the self-reduction process of Eu3+→Eu2+ occurs in this glass matrix. Meanwhile the intensity of NIR emission peaked at about 1300nm increases with the increase in the radius of alkali earth ions, while the intensity of both NIR emission peaked at about 1100nm and the red emission from Bi2+decreases. Then the origins of infrared-emitting bismuth centers were discussed according to the correlation of the conversion of Bi ions with the size of alkali earth ions. The results of this work is helpful for understanding the nature of Bi-NIR-emission and may be a guide for the selection of composition of high performance Bi-doped glass.
2013, 62 (11): 117802. doi: 10.7498/aps.62.117802
The photoluminescence (PL) properties of InN films grown by metal organic chemical vapor deposition (MOCVD) have been investigated. InN has a high level of background carrier concentration, which makes the Fermi level lie above the conduction band. By nonlinear fitting of the PL results, along with the energy band relations, we calculated the band gap of InN film to be 0.67 eV and the carrier concentration n=5.4×1018 cm-3. Thus we found a connection between PL results and the carrier concentration of InN films. In addition, we also studied the dependence of peak position and intensity of PL on temperature: the intensity of photoluminescence decreases as the temperature increases, and the peak position shows a red shift instead of an S-shape variation. Such a difference may be explained by a huge full width at half maximum of PL spectra. Also the concentration of carriers and the magnitude of the built-in electric field in the material may have influence on such a result.
Spectroscopic properties and energy transfer of Ce3+/Eu2+ codoped oxide glasses with high Gd2O3 concentration
2013, 62 (11): 117803. doi: 10.7498/aps.62.117803
Eu2+/Ce3+ single doped and co-doped oxide glasses with high Gd2O3 concentration were prepared in a reducing atmosphere using a high-temperature glass melting method. Excitation and emission spectra measurements indicated that Ce3+ can enhance the luminescence intensity of Eu2+ effectively, which exhibited a 2.3 times increasa. The difference between the luminescence lifetimes of Eu2+ with and without Ce3+ doping indicated that the energy transfer efficiency could reach 61.5%, for which the energy transfer mechanism was investigated further. These researches suggest that co-doping method can significantly improve the luminescence capabilities of Eu3+ in the oxide glasses with high Gd2O3 concentration.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Effects of annealing temperature on the microstructure and p-type conduction of B-doped nanocrystalline diamond films
2013, 62 (11): 118101. doi: 10.7498/aps.62.118101
Annealing of different temperatures was performed on boron-doped nanocrystalline diamond (BDND) films synthesized by hot filament chemical vapor deposition (HFCVD). Effects of annealing temperature on the microstructural and electrical properties of BDND films were systematically investigated. The Hall-effect results show that smaller resistivity and Hall mobility values as well as higher carrier concentration exist in the 5000 ppm boron-doped nanocrystalline diamond film (NHB) as compared with those in 500 ppm boron-doped nanocrystalline diamond film (NLB). After 1000 ℃ annealing, the Hall mobility of NLB and NHB samples were 53.3 and 39.3 cm2·V-1·s-1, respectively, indicating that annealing increases the Hall mobility and decreases the resistivity of the films. HRTEM, UV, and visible Raman spectroscopic results show that the content of diamond phase in NLB samples is larger than that in NHB samples because higher B-doping concentration results in a greater lattice distortion. After 1000 ℃ annealing, the amount of nano-diamond phase of NLB and NHB samples both increase, indicating that a part of the amorphous carbon transforms into the diamond phase. This provides an opportunity for boron atoms located at the grain boundaries to diffuse into the nano-diamond grains, which increases the concentration of boron in the nano-diamond grains and improves the conductivity of nanocrystalline diamond grains. It is observed that 1000 ℃ annealing treatment is beneficial for lattice perfection of BDND films and reduction of internal stress caused by doping, so that the electrical properties of BDND films are improved. Visible Raman spectra show that the trans-polyacetylene (TPA) peak (1140 cm-1) disappears after 1000 ℃ annealing, which improves the electrical properties of BDND films. It is suggested that the larger the diamond phase content, the better lattice perfection and the less the TPA amount in the annealed BDND samples that prefer to improve the electrical properties of BDND films.
Phase field crystal simulation of microscopic deformation mechanism of reverse Hall-Petch effect in nanocrystalline materials
2013, 62 (11): 118102. doi: 10.7498/aps.62.118102
The nanocrystalline (NC) materials of several average grain sizes ranging from 11.61 to 31.32 nm were obtained by using the phase field crystal model (PFC), and the microscopic deformation mechanism of strengthening law for the uniaxial tensile deformation was discussed. Simulated results show that grain rotation and grain boundary (GB) migration are mainly responsible for the microscopic deformation. Since small grain size is favorable for grain rotation so that it can make the yield strength reduced; and the NC materials would show a reverse Hall-Petch effect. When the grain size is so small and the strain exceeds the yield point to about 4%, dislocation activities begin to occur. Mainly by the change of GB structure (disorganizing triple grain boundary junction and then promoting grain migration), the GB can play a finite contribution to deformation. With increasing grain size, grain rotation becomes difficult, and the grain serration and emission of dislocations are observed.
Influence of applied magnetic field on properties of silicon nitride thin film with light trapping structure prepared by R.F. magnetron sputtering
2013, 62 (11): 118103. doi: 10.7498/aps.62.118103
In the applied magnetic field different magnetic intensities in the permanent magnet were introduced between the substrate and target, so as to study their influence on the properties of silicon thin films with light trapping structure prepared by R.F. magnetron sputtering. The microstructures, surface morphology and optical properties of the films were characterized by X-ray diffraction, atomic force microscope (AFM) and ultraviolet spectrophotometer separately. Results show that the silicon nitride thin films are still in amorphous state although an magnetic field was applied on them; however, when the magnetic field in the center is of 1.5 T, the surface morphology of the films has dramatically changed to a special peak structure, i.e. pyramid-like protuberances which are perpendicular to the basal surface; meanwhile, in the visible and near infrared range, the average transmittance of the sample is the highest, which is more than 90%, nearly twice as much as the transmittance of the sample without applied magnetic field, thus the light trapping effect is the great.
2013, 62 (11): 118104. doi: 10.7498/aps.62.118104
Thin films of ternary compounds CuxInyN were grown on Si (100) wafers by RF magnetron cosputtering at a low temperature, low power and pure N2 environment. The effect of In incorporation on the structure and physical properties of copper nitride was obvious, which was evaluated by characterizing the film chemical bonding state, structure, electrical and optical properties. In XPS, shift of binding energy, Auger peak and Auger chemical parameters all reflected the chemical changes in the environment. For samples with In content below 8.2 at.%, either the BE increasing of Cu 2p3/2 and In 3d5/2 or the decreasing of N1s could mainly contribute to the Cu-In-N bond formation. For the Cux InyN sample with 4.6% In, indium atoms were consistently confirmed to be incorporated into the body center of Cu3N anti-ReO3 structure as shown by XRD and TEM. The strong (001) preferred orientation of copper nitride crystalline phase was kept predominant in the films until the In content goes up to 10.8 at.%, the texture changed to (111) orientation. The R-T curves of CuxInyN films changed from typical exponential to linear with increasing In. Near constant electrical resistivity in a large temperature range with small TCR of -6/10000 was investigated in the CuxInyN sample with 47.9 at.% In. Moreover, the optical band gap, due to Burstein-Moss effect, was investigated to enhance from 1.02 to 2.51 eV with the In content increasing from 0% to 26.53%, accompanied with band-gap transition from direct to indirect.
There are many factors to influence the population behavior of cells. Except for the ways of cellular communication and the cellular environment, Which have been considered in the previous studies, the number of cells (or system size) that has been little considered before is also an important factor. This article investigates effects of system size on clustering behavior in a synthetic multicellular system, where individual oscillators are an integration of repressilator and hysteresis-based oscillators and are coupled through a quorum-sensing mechanism. By bifurcation analysis and numerical simulation, we find that increasing the cell number not only can change the size of the stability interval of steady state clusters and induce new clustering behaviors, but also benefits the enlargement of the attraction basin of steady state clusters, implying that cell differentiation may be closely related to the system size. In addition, such an increase can greatly extend the kinds and coexisting modes of steady state and oscillatory clusters, which would provide a good basis for the adaptability of organisms to the environment. Our results have extended the connotation of dynamics of coupled systems and also may be the foundation for understanding multicellular phenomena.
2013, 62 (11): 118702. doi: 10.7498/aps.62.118702
The interaction between DNA and counter-ions of different valence, including sodium chloride (Na+), magnesium chloride (Mg2+), hexammine cobalt III ([Co(NH3)6]3+), and spermine ([C10N4H30]4+), is investigated by dynamic light scattering. It is found that the ratio of electrophoretic motilities of DNA in a buffer containing Na+ and Mg2+ is about 2:1, when the concentration of counter-ions c≥ 5 mM. But the ratio of DNA motilities in a buffer containing Na+ and [Co(NH3)6]3+ is about 4.5:1. When c<5 mM, the ratio grows with increasing concentration of counter-ions. DNA charge reversal can be observed in the case of quadrivalent counter-ion. The experimental results are in good agreement with the Manning counter-ions condensation theory for cases of monovalent or bivalent counter-ions. However, when the valency of counter-ions is equal to three, the experimental data deviates from the expectation of the theory significantly. For the quadrivalent counter-ions, the counter-ions condensation theory, which is based on the average field, fails. Furthermore, through the atomic force microscopy, it is found that DNA molecules will condense into compact structures when the valency of counter-ions is equal to or greater than three. Thus, the conformation of polyelectrolyte in free solution and the ion correlation play an important role in the migration process of polyelectrolyte.
2013, 62 (11): 118703. doi: 10.7498/aps.62.118703
Current source reconstruction, i.e., reconstructing current dipole distribution through measured array signals of cardiac magnetic field on body surface, is a method for non-invasively study on the heart electrical activity. In this paper, the relationship between measured magnetic signals and current dipole distribution is described by a linear equation, and a sparse solution of current source reconstruction is achieved using a fast greedy method. This method can significantly decrease the computational complexity of or- thogonal matching pursuit (OMP) algorithm by means of approximating orthogonalisation and improving the selection vector strategy per iteration. Thereby, the sources with large dipole strength can be fast searched out with high accuracy. A set of magnetocardiogram (MCG) data of normal subject is used to demonstrate the effectiveness of this method that the trajectory of reconstructed dominant sources, whose strengths are more than 65%, is almost consistent with conduction process in depolarization and repolarization. The average goodness of fit (GOFs) of measured MCG and the magnetic field map generated by the reconstructed current sources during QRS complex and ST-T segment are 99.36% and 99.78%, respectively.
2013, 62 (11): 118704. doi: 10.7498/aps.62.118704
Brain is a complex nonlinear dynamic system consisting of related functional regions that can be described by the complex network model. Acupoint magnetic stimulation is an equivalent external stimulus for brain, which can be used as an important technical method to study the regulation mechanism of complex nervous system. It is of great significance to research the effect of acupoint magnetic stimulation on the structure and characteristics of brain functional network. Magnetic stimulation was applied to Neiguan (PC6) and the acquired EEG data were analyzed using dual-channel nonlinear method of mutual information in time domain. The corresponding brain functional networks before, during and after a magnetic stimulation were constructed and the characteristic parameters were studied based on the complex network theory. Results show that the average degree, average clustering coefficient and global efficiency of the brain functional network were increased under magnetic stimulation frequency of 3 Hz, while the average path length was reduced. The small world attribution of the corresponding functional network was enhanced, which made the information transfer among brain regions more efficiently. The brain functional networks under acupoint magnetic stimulation is studied for the first time as far as we know, which provides a new idea and approach to investigate the effect and regulation mechanism of transcutaneous acupoint magnetic stimulation to the complex nervous system.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (11): 119401. doi: 10.7498/aps.62.119401
Within the plasma environment of spacecraft, the interaction between electrons and ions may cause surface charging and discharging and may degrade the performance of spacecraft. The charging potential is a key factor for discharging process. By considering the comprehensive effects of particle mass, temperature, density of plasma, secondary electrons and the velocity of unbiased solid, a general equation of surface charging potential of unbiased solid has been derived using Maxwell velocity distribution function. The expressions under some special and general conditions have been also analyzed. The surface charging and discharging properties are summarized under different plasma environment and motion states of unbiased solid.
2013, 62 (11): 119701. doi: 10.7498/aps.62.119701
In this paper a high resolution X-ray simulation source is proposed and designed to verify the navigation based on X-ray pulsar in the simulation experience system. The simulation source consists of an arbitrary signal generator and a grid controlled X-ray tube. According to the grid tube's characteristic curve, the data of the pulsar standard pulse template are converted. Then using the method of direct digital frequency synthesis, the converted data are synthesized to waveforms, called the analog modulated grid voltage. In the grid controlled X-ray tube, the grid voltage changes the number of electrons hitting on the target and controls the X-ray intensity. With an analog modulated pulse profile applied on the tube grid electrode, the tube will emit X-rays which will match photons' statistical distribution and simulate the X-ray pulsar profile extremely well. The properties of Crab pulsar simulation source are tested in X-ray pulsar navigation simulation experience system. The results of the test are as follows: Comparing the tested pulse profile with the standard pulsar profile, we have time correlation coefficient is 0.9774, and frequency correlation coefficient is 0.9853. The X-ray photon flux is 1.90 ph·cm-2·s-1, the pulsed fraction is 76.15%, and the half-width half maximum is 1.879 ms. These results show that the X-ray simulation source has several merits, such as: strong ability to simulate the X-ray, low cost and simple operation. So it is an important means for the improvement of X-ray pulsar navigation.