Vol. 59, No. 7 (2010)
2010-04-05
GENERAL
2010, 59 (7): 4403-4408.
doi:10.7498/aps.59.4403
Abstract +
The expressions of shock solutions for singularly perturbed Robin problem of nonlinear equations are constructed using the matching method. The conditions for appearance of shock near the boundary are discussed.
2010, 59 (7): 4409-4412.
doi:10.7498/aps.59.4409
Abstract +
A class of singularly perturbed initial boundary value problems for nonlinear reaction diffusion equations with two parameters are considered. Under suitable conditions, the asymptotic expansion of the solution is constructed and the asymptotic behaviors of the solution are discussed.
2010, 59 (7): 4413-4419.
doi:10.7498/aps.59.4413
Abstract +
Based on the auxiliary equation method, the nonlinear superposition formula for the solutions of the second kind of elliptic equation is proposed. It is also used to construct the infinite sequence of new exact solutions to the generalized Boussinesq equation with the aid of symbolic computation system Mathematica. The infinite sequences of exact solutions include the Jacobi elliptic function infinite sequence solutions, the solitary wave infinite sequence solutions and the triangular function infinite sequence solutions. And the method is of significance to seek infinite sequence exact solutions to other nonlinear evolution equations.
2010, 59 (7): 4420-4425.
doi:10.7498/aps.59.4420
Abstract +
With a projective equation method and a variable separation method, new families of variable separation solutions (including solitory wave solutions, periodic wave solutions, and rational function solutions) for (3+1)-dimensional Burgers system is derived. Based on a derived solitory wave solution and a rational function solution, we obtain some novel localized structures such as instantaneous embed soliton and instantaneous taper-like soliton.
2010, 59 (7): 4426-4433.
doi:10.7498/aps.59.4426
Abstract +
A new particle filter based on interval filter and particle diffraction is proposed for the on-line estimation of non-Gaussian and nonlinear system with uncertain dynamics modeling. This algorithm computes the more accurate importance density function, which integrates the latest observations into the system state transition density, so that the approximation to the system posterior density is improved. At the same time, the workload of calculation is reduced by treating particle diffraction like light diffraction. A simulation experiment on the SINS/CNS (strap-down inertial navigation system/celestial navigation system) attitude estimation shows the effectiveness and robustness of the improved algorithm.
2010, 59 (7): 4434-4436.
doi:10.7498/aps.59.4434
Abstract +
The Rosenberg problem is a typical but not a too complex problem of nonholonomic mechanical systems. By using the theory of Noether symmetries of nonholonomic systems, the conserved quantities of the problem is successively deduced,and the final result is obtained.
2010, 59 (7): 4437-4441.
doi:10.7498/aps.59.4437
Abstract +
The symplectic description and transformed condition of canonical transformation are discussed in mechanics. The condition in thermodynamics is proved. The canonical transformation in electromagnetic waveguide is also studied. The conclusion shows that mechanics, thermodynamics and electromagnetic waveguide have a similar structure in symplectic system. It presents a useful attempt to unified theories.
EDITOR'S SUGGESTION
2010, 59 (7): 4442-4452.
doi:10.7498/aps.59.4442
Abstract +
To overcome the internal limitation of standing wave forces on vertical breakwaters and describe multichromatic multidirectional water waves in front of the breakwaters, a third-order theory, including the classical solutions of two-dimensional long-crested waves and monochromatic unidirectional short-crested waves, for bichromatic bidirectional water waves partially reflected from the breakwaters is developed. A universal law applicable to a higher-order multichromatic multidirectional wave system is proposed, that is, the even-order frequencies are zero, the numbers of the odd-order frequencies constitute a geometric progression.
2010, 59 (7): 4453-4459.
doi:10.7498/aps.59.4453
Abstract +
We have studied the sudden death and revival of entanglement in two V-type three-level atoms coupled to the common vacuum. results show that in the case of largely separated atoms, spontaneous emission leads to decoherence and even causes entanglement sudden death. However, the excited-state decay rate of the atom can affect the time of entanglement sudden death. In the case of closely separated atoms, due to the collective effect of atoms, the entanglement which has been dead will revive in some time. The initial entanglement and the revival of entanglement arise from different causes.
2010, 59 (7): 4460-4465.
doi:10.7498/aps.59.4460
Abstract +
The performance of an irreversible engine consisting of a nonlinear diodes system is presented. The system consists of two diodes switched in the opposite directions and located in two reservoirs at different temperatures, and the two diodes are connected in parallel with a capacitor. Based on the theory of thermal fluctuations, the expressions of the heat fluxes absorbed from the hot and cold reservoirs are derived. When the heat leak between the two reservoirs is taken into account, the power output and the efficiency of the engine can be obtained. The performance characteristic curves are plotted and the characteristic relations between the optimum performance parameters and the ratio of the temperatures are obtained by numerical simulation. The influence of the main parameters, including the nonlinearity of the diodes, the loss of heat leak and the ratio of temperatures of two reservoirs, on the performance characteristics of the engine is analyzed in detail. Finally, the performance characteristics of the ideal diodes engine are discussed.
2010, 59 (7): 4466-4471.
doi:10.7498/aps.59.4466
Abstract +
An internal ratchet model is established, in which a force-free system is coupled to a subsystem with asymmetric periodic structure, while the latter is in a thermal bath environment. The average velocities of particles driven by a periodic signal in two ways are calculated respectively. In comparison with the result of external ratchet with the same parameters, our results show that the maximum directional current of particles in internal ratchet is larger than that in external ratchet. Under the same temperature, the particles in the internal ratchet are more prone to directional movement.
2010, 59 (7): 4472-4479.
doi:10.7498/aps.59.4472
Abstract +
A kind of novelty detection method based on retina neural network is proposed, which could find the novelty in chaotic time series. To demonstrate the capability of the novelty detection method, we designed three novelty detectors,namely the neural network novelty detector (RNNND), back-propagation(BP) novelty detector (BPND) and radial base function(RBF) novelty detector (RBFND), which are based on retina neural network, BP neural network and RBF neural network, respectively. Using Lorenz time series and oil pipeline pressure time series, we tested the performance of the three novelty detectors, including performances of anti-jamming, micro-novelty detection and the computing speed. The results show that the three novelty detectors have good precision and fast computing speed. Finally, the merits and shortcomings of the proposed novelty detection method are analyzed based on retina neural network, BP and RBF neural network, and their applicabilities are given.
2010, 59 (7): 4480-4484.
doi:10.7498/aps.59.4480
Abstract +
Electroencephalogram (EEG) shows long-range power-law and multifractal scaling behaviors, which varies with physiological and pathological conditions. In the present paper, the scaling behavior of sleep EEG is studied using monofractal detrended fluctuation analysis (DFA) and multifractal singularity spectrum. It is found that, the DFA scaling exponent α is more sensitive to the differences between EEG derivations and subject groups, but irregular with sleep stages. However, the variation of multifractal singularity strength range Δα with sleep stages is more regular, it increases constantly from sleep stage Ⅰ to stage Ⅳ, showing less difference between EEG derivations and subject groups. Thus, it is suggested that multifractal parameter Δα is more suitable than monofractal scaling exponent α to be used as a quantitative parameter for sleep staging.
2010, 59 (7): 4485-4489.
doi:10.7498/aps.59.4485
Abstract +
The influence of noise on the dynamics of a two-dimensional neural map with self-sustained subthreshold oscillations is studied by numerical simulation. When the injected current is absent and the control parameter is located in the silence region, numerical results show that stochastic oscillations of the membrane potential can be induced by noise. Moreover, the coherence of such oscillations shows two maxima with the variation of the noise strength. The effect of control parameter on the dynamics of the system has also been investigated. Interestingly, it is found that the occurrence of coherence bi-resonance is closely associated with the distinct characteristics of the bifurcation of the deterministic dynamics.
2010, 59 (7): 4490-4498.
doi:10.7498/aps.59.4490
Abstract +
On the basis of the research of driving behavior, by analyzing the mechanism of driving behavior and using the cellular automaton (CA) model, we introduce the mechanism of driving behavior, which is associated with the vehicle’s own speed, the relative speed, the vehicle spacing, and the safety vehicle spacing, into the CA model (ACA). We observe the metastability, phase-separation and hysteresis phenomena when taking advantage of ACA model to conduct the microscopic traffic simulation and compare the simulation results of ACA model with the simulation results of the CA model (BCA) which only considers the vehicle’s own speed and the vehicle spacing. The results show that, in the macro level, from the maximum traffic flow, stability and the efficiency in dissolving congestions, the simulation results of ACA model exhibit a larger maximum value of flow which is also closer to the actual measured data, stronger stability and higher efficiency of dissolving jam; in the micro level, from the fluctuations of the vehicles’ speed and the vehicles’ headway-distance, the simulation results of ACA model exhibit that the vehicles do not accelerate or decelerate suddenly, the vehicles can be relatively and evenly distributed on the road. All these results illustrate that the relative speed and safety vehicle spacing have a significant impact on the driving behavior and also explain that the ACA model is in better consistence with the actual situation and has some practical significance.
2010, 59 (7): 4499-4507.
doi:10.7498/aps.59.4499
Abstract +
Simulation of pedestrian evacuation flow with affected visual field is carried out on the basis of cellular automata. The room to be evacuated is divided into exit visible area, wall visible area and blind area by pedestrian sight radius, and two basic dynamic parameters in the dynamic parameters model are used to simulate the varied movement characteristics of pedestrian in different evacuation areas, including normal evacuation movement, movement along the wall and movement in fixed direction. The effect of pedestrian sight radius on evacuation time is studied with evacuation signs on the wall and pedestrian stochastically moving to find the wall in fixed directions and then moving along the wall. It is observed that the evacuation time depends not only on the pedestrian sight radius but also on the length and utilization rate of exit.
2010, 59 (7): 4508-4513.
doi:10.7498/aps.59.4508
Abstract +
The H2+He fluid mixture will be dissociated into a three-component mixture composed of H2 molecules, H and He atoms at high temperatures and high pressures. The dissociation energy of H2 molecule will be lowered due to the interactions between all these particles. In this paper, the self-consistent fluid variational theory is used to calculate the equation of state of H2+He fluid mixture in the region of partial dissociation, in which the various interactions between particles and the correlation contributions to the dissociation energy caused by both the temperature and pressure effects are taken into account. The dissociation degree and thermodynamic parameters are obtained from nonideal dissociation equilibrium, which is determined self-consistently by the free energy function. Comparison was made with the available shock-wave experiments, other theoretical calculations and Monte Carlo simulations.
2010, 59 (7): 4514-4523.
doi:10.7498/aps.59.4514
Abstract +
To analyze the dynamic of crude oil price data using homogenous partition of coarse graining process,OK WTI Spot Price FOB from January 1986 to November 2009 was transformed into symbolic sequences consisting of three characters (R,e,D). The vertices of the oil price fluctuation network were 5-symbol strings in the number of 102(i.e.102 fluctuation patterns in durations of 5 days) linked in the network's topology by time sequence. It contained integrated information about interconnections and interactions between fluctuation patterns of oil price in network topology. The dynamical statistics of the degree, degree distribution, clustering coefficient and the shortest path length were calculated. The results indicated that the degree of the oil price sequence fluctuation network and the accumulated degree distribution show a power-law distribution, so did the node degree and the rank. The degree of the former 32 nodes was larger, and most oil price fluctuation models had the character with the escalating trend. Some nodes of the oil price fluctuation network had stronger ability in between centrality, and 24.5 percent of the nodes took part in the 80.97 percent of Between Centrality function. The average path length was 2.285, and the paths with length 2—3 were 86.8 percent, which verified the complex characteristics of the oil price fluctuation in network topology. This paper had guiding significance in identifying the topological importance of the node model and understanding the inherent law and information of the oil price fluctuation.
2010, 59 (7): 4524-4529.
doi:10.7498/aps.59.4524
Abstract +
A new optimized structure of an UTC (uni-traveling-carrier) photodiode is developed and epitaxied by metal-organic chemical vapor deposition. We fabricated a UTC photodiode of 30 μm in diameter. Theoretical simulation based on drift-diffusion model was used to analyze the space-charge-screening effect in UTC photodiode primarily in two aspects: the carrier concentrations and the space electric field. The simulation results were generally in agreement with the experimental data.
2010, 59 (7): 4530-4534.
doi:10.7498/aps.59.4530
Abstract +
The black-nickel film on the flat type radiometer chip was investigated, and a black-nickel film which can be applied in this chip was prepared using electroplating method. The analyses of absorption of radiometer chip indicated that the absorption rate of the chip is proportional to the surface roughness. The black-nickel film was prepared and tested, and surface morphology testing showed that this film has microstructures of the scale 50 nm—1.5 μm. Infrared absorption measurement indicated that the absorptivity of the film in the 1.4—8 μm range is higher than 0.989. This high absorptivity black-nickel film improves the performance of the chip.
NUCLEAR PHYSICS
2010, 59 (7): 4535-4541.
doi:10.7498/aps.59.4535
Abstract +
The detection of chemical speciation with spatial resolution of 30 nm has been implemented at BL08U soft X-ray spectromicroscopy endstation of Shanghai Synchrotron Radiation Facility. For each specimen, we scan two absorption images separately at two energies E1 and E2 near the absorption edge of the element with E1>E2. After calculating the signal ratio of each pair of the corresponding pixels’ optical density in the two absorption images, we can obtain the map of the spatial distribution of that element. Compared with the conventional analysis method of K-edge subtraction (KES), our ratio analysis method is more sensitive and accurate in identifying the spatial distribution of the interested elements, and the definition of the contrast threshold determining whether a pixel contains the interested element, is simpler and clearer in physics. Through the analysis and calculation of the spatial distributions of the oxygen element on a pre-oxidized polyacrylonitrile fiber cross-section, we can verify the effectiveness of the ratio analysis method compared to the traditional KES method. This ratio method provides a new analysis tool for fast mapping the distribution of trace elements.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (7): 4542-4546.
doi:10.7498/aps.59.4542
Abstract +
Quadratic configuration interaction (QCISD) method has been used to optimize the possible ground state structures of MgB and MgB2 by the 6-311G and 6-311++G(df) basis sets. The potential energy functions of MgB2 have been derived from the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules. Molecular reaction kinetics of B+MgB and Mg+BB based on the potential energy functions is discussed briefly, which is successfully used for describing molecular reaction dynamics.
2010, 59 (7): 4547-4555.
doi:10.7498/aps.59.4547
Abstract +
Based on the variation principle, many methods have been developed in atomic structure calculations. A high quality complete basis set is essential to the calculation of atomic structures. We present how to construct quasi-complete basis sets through Dirac-Fock calculations and multi-configuration Dirac-Fock self-consistent filed calculations by using the full-relativistic GRASPVU program package, which is based on the multi-configuration Dirac-Fock method. The relativistic configuration interaction calculations are carried out by using the quasi-complete basis sets to adequately consider correlations. The relativistic retardation effect of electromagnetic interactions and the quantum electron dynamic corrections are also taken into account. Our calculation results of He agree well with other theoretical results and experimental results, which validates the feasibility of our calculation scenario. Our calculations are full-relativistic, and can be extended to high Z helium-like ions in which the relativistic effect is important. Our scenario of constructing quasi-complete basis sets can be used in any many-electron atomic system. We calculated the energy levels of Mg and elucidated the mechanism of its interesting fine-structure splittings of 3 3D and 4 3D levels.
2010, 59 (7): 4556-4563.
doi:10.7498/aps.59.4556
Abstract +
The potential energy curves (PECs) for the ground electronic state X4Σ-and five low-lying excited electronic states (a2Π, b2Δ, c2Σ-, d2Σ+, A4Π) of LiC have been calculated using the multiconfiguration reference configuration interaction method including Davidson correction (MRCI+Q). And PECs were fitted to analytical Murrell-Sorbie potential function to deduce the spectroscopic parameters of equilibrium bond length Re, rotation coupling constant ωe, anharmonic constant ωeχe, equilibrium rotation constant Be and vibration-rotation coupling constant αe. Those values were also compared with the other results currently available. By solving the radial Schrdinger equation of nuclear motion, the vibration levels, inertial rotation constant and six centrifugal distortion constants (Dν, Hν, Lν, Mν,Nν,and Oν) are reported for the first time.
2010, 59 (7): 4564-4570.
doi:10.7498/aps.59.4564
Abstract +
By solving the one-dimensional time-dependent Schr?dinger equation with split-operator method, we study the high harmonics generated by helium atom, and analyse the characteristics of the attosecond pulses generated by the high-order harmonics. By adopting a mid-infrared driving pulse (with wavelength of 2000 nm and pulse duration of 12.5 fs) combined with a short UV controlling pulse, a smooth supercontinuum with the bandwidth of 230 eV is observed. By adjusting the delay between the mid-infrared and ultraviolet fields, the contribution of the short quantum trajectory can be efficiently enhanced and an isolated 100 as pulse seems achievable. We found that the supercontinuum is not sensitive to the intensities of the two lasers, which facilitates the experimental implementation for the isolated attosecond pulse generation.
2010, 59 (7): 4571-4576.
doi:10.7498/aps.59.4571
Abstract +
Laser-induced breakdown plasma is produced by using Q-switched Nd: YAG laser operating at 532 nm, which interacts with the Al alloy sample target in air. The spectral lines in the 230—440 nm wavelength range have been identified, and based on the calibration-free method, the mass concentration of Al alloy are obtained, which is in good agreement with the standard value of the sample.
2010, 59 (7): 4577-4583.
doi:10.7498/aps.59.4577
Abstract +
Based on the algebraic method (AM) proposed to calculate accurate full vibrational energies for diatomic molecules in Sun’s previous work, the parameter-free analytical formula for dissociation energy of diatomic system is used to study the dissociation energies and the full vibrational spectra of 5 electronic states of Li2 molecule in this work. The results show that the AM vibrational spectra and dissociation energies are in excellent agreement with experimental results.
2010, 59 (7): 4584-4590.
doi:10.7498/aps.59.4584
Abstract +
We utilize slow highly charged ions of Xeq+ and Pbq+ to irradiate GaN crystal films grown on sapphire substrate, and use X-ray photoelectron spectroscopy to analyze its surface chemical composition and chemical state of the elements. The results show that highly charged ions can etch the sample surface obviously, and the GaN sample irradiated by highly charged ions has N depletion or is Ga rich on its surface. Besides,the relative content of Ga—Ga bond increases as the dose and charge state of the incident ions increase. In addition, the binding energy of Ga 3d5/2 electrons corresponding to Ga—Ga bond of the irradiated GaN sample is smaller compared with that of the Ga bulk material. This can be attributed to the lattice damage, which shifts the binding energy of inner orbital electrons to the lower end.
2010, 59 (7): 4591-4597.
doi:10.7498/aps.59.4591
Abstract +
Multiple hard-ellipsoid model is a theoretical model which can more accurately decribe collisions between He atom and Na2 molecule. In this paper, we adopted the multiple hard-ellipsoid model to calculate the integral cross sections of rotational excitation for collisions in 3He,4He,7He,10He-Na2 systems at different relative incidence energies. This study shows that we can improve the accuracy of the results by increasing the number of equipotential ellipsoid surfaces. Moreover, we find that the integral cross sections of rotational excitation change with the relative incidence energy and reduced mass of the system. Finally, at relative incidence energy of 100 meV, we investigate the influence of different regions of the intermolecular potential on integral cross sections of rotational excitation in 4He-Na2 collisions.
2010, 59 (7): 4598-4601.
doi:10.7498/aps.59.4598
Abstract +
Geometric structures of (SiO2)n-(n≤7)anion clusters are optimized by using the generalized gradient approximation density functional theory. The energy and vibrational frequency have been calculated. The lowest energy (SiO2)4- cluster is found to be more thermodynamically favored compared with other neighboring sized cluster isomers. Additionally,the lowest energy (SiO2)n-(n≥4)clusters grow up regularly based on the lowest energy (SiO2)4- cluster.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (7): 4602-4606.
doi:10.7498/aps.59.4602
Abstract +
The paper presents a single-sided double-S left-handed metamaterial structure in the X-band. The left-handed property of the new metamaterial has been verified by numerical simulation and experiment. Experimental results show the existence of the negative refraction within the same frequency band as indicated by the simulation. The proposed structure makes it easy to fabricate and feasible to make controllable metamaterial by incorporating itself with controllable elements.
2010, 59 (7): 4607-4611.
doi:10.7498/aps.59.4607
Abstract +
Based on Maxwell’s equations’ form-invariance to coordinate transformations, an electromagnetic cloaking structure at 10.14 GHz was designed by cylindrical coordinate transformation and made with metamaterial composed of split-ring resonators. A quick novel experiment method was used to measure the power level of the received microwave signal. The cloaking structure reduced scattering from the hidden object and meanwhile reduced its shadow effect, which was consistent with theoretical expectations. The experiment system reduced the complexity and shortened the time of measurement, which provided a new simple and effective experimental method in this field.
2010, 59 (7): 4612-4619.
doi:10.7498/aps.59.4612
Abstract +
A lossy ceramic-loaded waveguide is positive to promote the stability and performance of the gyrotron traveling-wave amplifier (gyro-TWT). In this paper we develop the electron cyclotron maser linear theory on the basis of the field expressions in the lossy ceramic-loaded waveguide. By systematic numerical calculation, we find that both the field patterns and the dispersion curves have one-to-one mapping relation between the modes in ceramic-loaded waveguide and that in empty cylindrical waveguide. With the Laplace transform, the linear theory could calculate the field profile and the threshold of an absolute instability oscillation. The linear theory is also used to study the influence of the magnetic, current and ceramic layer on the amplification characteristics. These results are promotive to the application of the lossy ceramic in a gyro-TWT and the development of the high stable gyro-TWT.
2010, 59 (7): 4620-4625.
doi:10.7498/aps.59.4620
Abstract +
The realization technique of modularization on the long pulse high power generator was expounded. The relation between the ferromagnetic dissipation of the linear transformer and the exciting magnetic current was analyzed. The main influential factors on the wave distortion from the primary pulse to the system output waveforms were discussed. Finally, through engineering experiments, a long pulse power electron beam of up to several gigawatt with repetition frequency of several dozen hertz and rise time of 40—50 ns was obtained. This paper gives a new idea for research on the modularization of the long pulse high power generator with higher repetition rate.
2010, 59 (7): 4626-4633.
doi:10.7498/aps.59.4626
Abstract +
The sheet electron beam with a quasi-rectangular cross section has been proposed to carry intense current. Obviously different from the elliptical sheet electron beam with the same high aspect ratio, this kind of beam is almost uniform in thickness, and can be generated by the cold metal cathode. Besides, the uniform thickness leads to uniform beam power in the horizontal direction, implying less modes but better counteraction between the beam and microwave. In addition, the uniform thickness make the width of the propagation system,including the cold cathode, the microwave cavities and the focusing magnets,easily changed. Firstly,the space-charge electric field of the sheet electron beam was analyzed numerically, then the focusing magnets, including the periodic cusped magnets and quadrupole magnets, were designed according to the space-charge electric field for beam matching. To validate the above theoretical analysis, particle-in-cell simulation was performed, which shows that the 300 keV, 3 kA sheet electron beam can be well focused by the 0.163 T periodic cusped magnetic fields with the 0.064 T quadrupole magnetic fields. More than 98% of the total current has been propagated through the distance of 300 mm.
2010, 59 (7): 4634-4639.
doi:10.7498/aps.59.4634
Abstract +
Speckle contrast in laser scanning display system with circular and rectangular laser spot on screen was calculated. For scanning with circular laser spot, the speckle contrast reduces with the decrease of the diameter of laser spot when the diameter of the laser spot is lager than the correlation length of the screen. When the laser spot is about the same size of the correlation length of the screen, the speckle contrast becomes higher owing to the non-Gaussian speckle effect. If we continue to reduce the size of laser spot, because of the specular reflection the speckle contrast decreases quickly. To ensure enough scattering elements in laser spot, the laser spot is just narrowed in one direction. If the laser spot is narrowed in the scanning direction, the speckle contrast is reduced due to the reducing temporal correlation of speckle, while if the laser spot is narrowed in the other direction, speckle contrast changes slightly. For the circular laser spot, some experimental results are given.
2010, 59 (7): 4640-4645.
doi:10.7498/aps.59.4640
Abstract +
The terahertz(1012Hz)spectra, Raman spectra and infrared-visible-UV spectra are analyzed for PbB4O7 crystal sample. A resonance peak appears in the curve of the dielectric function ε(ν) in the frequency range of 0.25—2.5 THz. The analysis supports that soft optical phonons exist in PbB4O7 crystal from four aspects: 1) the change curve ε(ν) of the dielectric function satisfies the Lyddane-Sachs-Teller relation; 2) a strong Raman scattering peak appears in the vicinity of resonance frequency (3.10 THz); 3) absorption coefficient curve α(ν) meets the characteristics of polaritons; 4) the dispersion relation curve ν(k) of the photon transmitting from the crystal reveals a frequency gap. The soft optical phonon exists in PbB4O7 crystal, which means that the frequency curve of the photon transmitting from the crystal will suffer splitting when the condition of producing polariton is satisfied. And the dispersion curve splits a higher branch and a lower one. This may help us find a new method of changing the frequency of the photon.
2010, 59 (7): 4646-4655.
doi:10.7498/aps.59.4646
Abstract +
Assuming the object surface is a scattering plane and both the reference beam and the reconstructing beam are spherical waves, we study the light wave field of object beam field reconstructing plane of off-axis digital holography in detail. The object beam, the conjugate object beam and the distribution of zero-order diffraction beam as functions of the optical system parameters are obtained. According to the characteristics of digital color holography, an optical system design method for suppressing zero-order diffraction interference is proposed. Furthermore, an optimization study has also been conducted on the wave front reconstruction algorithm to avoid interpolation error. Finally, the corresponding experimental verifications are given.
2010, 59 (7): 4656-4660.
doi:10.7498/aps.59.4656
Abstract +
One short-cut transformation from one-dimensional (1D) to three-dimensional (3D) spatial optical lattices is simulated and studied. By adding mirror-symmetric beams for 3 original beams, the interference patterns from 2D to 3D can be obtained. Furthermore, by selecting appropriate polarization of the interference beams, the 3D structure can become 1D layered structure, and the period of the layers can reach the sub-wavelength. This result offers an alternative method to produce 1D and 3D photonic crystals, especially for the fabrication of optical band gap structures.
2010, 59 (7): 4661-4671.
doi:10.7498/aps.59.4661
Abstract +
We study the nonclassicality and decoherence in photon-loss channel of generalized squeezed Fock state, which is related to the squeezed operator with three real parameters. By using the Weyl ordering invariance under similarity transformations and the technique of integration within an ordered product of operators, we obtain the compact Wigner function of the generalized squeezed Fock state (Laguree-Gaussian function). According to the integration formula of the time evolution of the Wigner function, the Wigner expresssion in photon-loss channel is analytically deduced. In particular, we discussed the nonclassicality from the negativity of the Wigner function.
2010, 59 (7): 4672-4676.
doi:10.7498/aps.59.4672
Abstract +
One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The dependence of species concentration and optical parameters on single pulse energy and pulse duration is studied. The dynamical process is analyzed while laser is running. Gain switching during lasing is discussed.These results can provide theoretical support for the optimization of pulsed chemical oxygen-iodine laser.
2010, 59 (7): 4677-4681.
doi:10.7498/aps.59.4677
Abstract +
In high vacuum environment of 10-3 Pa, using 355 nm pulsed ultraviolet(UV) laser we repeatedly raster scanning fused silica at energy density of under zero probability damage threshold, with the purpose of studying the change in anti-damage ability of fused silica after receiving different UV laser irradiation dosages in high vacuum. The damage measured after irradiation and increasing of damage pit indicate that the anti-damage ability of fused silica obviously drop, the degree of depression is more closely correlated with the irradiation time, while the influence of irradiation energy density is weak. The measurement of fluorescence excitation and X-ray photoelectron spectros copy proves that the increase of oxygen-deficiency in fused silica is the main cause, and the degree correlates with the received UV laser irradiation dosage.
2010, 59 (7): 4682-4686.
doi:10.7498/aps.59.4682
Abstract +
A novel modified method for realizing long-distance self-adaptive compensation optical fiber transmission is proposed. Based on the hybrid Raman amplification achieved by combining the original bi-directional Raman pump with a second Raman amplification generated by a fiber laser formed by a fiber Bragg grating pair with high reflectivity, the signal light is amplified effectively and the longest self-adaptive compensation optical fiber transmission distance of 125 km is achieved in experiment for the first time, to the best of our knowledge. In addition, the ON/OFF gain, amplified spontaneous emission noise, noise figure and the signal power distribution characteristics of the system are studied experimentally and theoretically. The experimental results are in good agreement with the theoretical analysis.
2010, 59 (7): 4687-4693.
doi:10.7498/aps.59.4687
Abstract +
The optical nonlinearity, including the nonlinear absorption, the nonlinear refraction and the third-order nonlinear polarizability of 2-(2'-hydroxyphenyl)benzothiazole (HBT) in cyclohexane, has been investigated using a single-beam Z-scan technique. The experiment and calculations show that HBT molecules have obvious two-photon absorption (TPA) effect under the 532 nm picosecond pulsed laser irradiation. The values of the TPA coefficient β0 for different pulse irradiance and the corresponding imaginary part χ(3)I of the third-order nonlinear polarizability were determined according to the open-aperture Z-scan results. Then we measured the nonlinear refractive index γ and the real part χ(3)R of the third-order nonlinear polarizability of HBT, and calculated these two nonlinear parameters with "Gaussian decomposition" method according to the close-aperture Z-scan and open-aperture Z-scan results, when the nonlinear refraction was accompanied by nonlinear absorption. The theoretical results agree very well with the experimental results. This work provides a theoretical as well as a experimental basis for further research and development of the application of the material.
2010, 59 (7): 4694-4700.
doi:10.7498/aps.59.4694
Abstract +
Assuming a Gaussian-shaped input signal pulse, we deduced the analytical expression of the output-pulse amplitude envelope in the Brillouin slow light system utilizing broadband pump with a rectangular spectrum under small-signal gain approximation. The expression is applicable in case that the pump spectrum has a sharp rising or trailing edge and a flat top. The influence of the fiber dispersion, the stimulated Brilouin scattering (SBS) gain non-uniformity and the SBS-gain-induced dispersion on the pulse distortion has also been quantitatively analyzed. The calculated results show that the analytical solution agrees well with the numerical one if the spectrum of the signal pulse lies in the pump spectrum. SBS-gain-induced third-order dispersion is the main physical factor responsible for the pulse distortion, which also limits the retardation increase of the short pulse in the cascaded Brillouin slow light system.
2010, 59 (7): 4701-4706.
doi:10.7498/aps.59.4701
Abstract +
Steady-state incoherently coupled screening photovoltaic spatial soliton pairs are predicted for biased photorefractive crystal circuit with a divider resistance. All kinds of the incoherently coupled spatial soliton pairs can be obtained from this theory by adjusting the values of the divider resistance, the biased electric field and photovoltaic electric field, such as the incoherently coupled screening spatial soliton pairs in biased photorefractive crystal with or without a divider resistance, the photovoltaic spatial soliton pairs in open-circuit, the photovoltaic spatial soliton pairs in close-circuit with or without a divider resistance, the screening-photovoltaic spatial soliton pairs in biased photovoltaic-photorefractive crystal with or without a divider resistance. Previous theories advanced individually elsewhere for these soliton pairs can be obtained by simplifying this theory under appropriate conditions.
2010, 59 (7): 4707-4714.
doi:10.7498/aps.59.4707
Abstract +
By applying the variational method, we studied a kind of dipole soliton in the nonlocal nonlinear Kerr media. The parameter coupling equations of the dipole soliton were obtained, and numerical simulations were carried out. The results show that the transverse intensity distribution of the dipole soliton is similar to Hermite-Gaussian shape under the condition that the dipole soliton has a high energy which approaches the case of strongly nonlocal nonlinearity. There is a platform between the two intensity peaks of the dipole soltion under the condition that the dipole soliton has a low energy which belongs to the case of weakly nonlocal nonlinearity.
2010, 59 (7): 4715-4719.
doi:10.7498/aps.59.4715
Abstract +
The principle of electric resonance metamaterial design is analyzed in detail, and the designed metamaterial (H-shaped metamaterial) is significantly miniaturized due to the lowering in the operating frequency from 12.21 to 5.46 GHz while keeping the dimensions unchanged, which was achieved by means of equivalent inductance and capacitance loading and grounding based on the equivalent circuit model. Our work not only provides a reference for miniaturizing different metamaterial configurations, but also points out specific research directions and effective ways in the design of metameterials with different characteristics and different operating frequencies.
2010, 59 (7): 4720-4725.
doi:10.7498/aps.59.4720
Abstract +
A kind of linerly tapered microstructure fiber has been proposed in this paper. The central wavelength, which is located in the anomalous dispersion region, is 1550 nm. We use an adaptive split-step Fourier method to numerically study the propagation of 1 ps laser pulse in this microstructure optical fiber. For the tapered fiber under consideration, a compression factor of 56.9 and a quality factor of 27 can be achieved in a fiber 1 m long. With the pulse shape evolution in the fiber, we find that in anomalous dispersion region, the pulse can be highly efficiently compressed by the increasing of nonlinearity coefficient and the decreasing of dispersion coefficient. Compared with the normal photonic crystal fibers, the thicker end of the tapered fiber is apt to be coupled to the laser pulse which has a larger effective mode area.
2010, 59 (7): 4726-4731.
doi:10.7498/aps.59.4726
Abstract +
The multi-pole method is used to analyse and compare the dispersion coefficient, dispersion slope, nonlinear coefficient, confinement loss of photonic crystal fibers of hexagonal, octagonal and decagonal structures with the same structure parameters. The photonic crystal fiber with hexagonal structure is more suited for study of dispersion compensation and high nonlinearity. The nonlinear coefficient of photonic crystal fiber with hexagonal structure is 0.37 m-1·W-1 at 0.8 μm. The photonic crystal fiber with decagonal structure is more suited for study of flat dispersion curve and low confinement loss.The confinement loss of photonic crystal fiber with decagonal structure is about 3000 orders of magnitude less than that with hexagonal structure around 0.8 μm.The dispersion of photonic crystal fibre with decagonal structure is less than 0.17 and larger than -0.07 ps/(km·nm) from 1.4 to 1.65 μm, resulting in nearly zero dispersion of photonic crystal fiber around 1.55 μm. The cladding structure of photonic crystal fiber is closer to the circular structure, the dispersion of which is much flatter, the nonlinear coefficient and the confinement loss of which are much lower.
2010, 59 (7): 4732-4737.
doi:10.7498/aps.59.4732
Abstract +
The sensitivity of an interferometer based on intermodal interference in photonic crystal fiber (PCF) has been investigated theoretically and numerically. Using the intermodal interference theory and the normalized frequency of PCF, we have analyzed the principle of the method for measuring refractive index by PCF interferomter,and obtained a variation, δns, to show the sensitivity of the PCF interferometer. From the analysis of the underlying physics of δns, we find that air holes of the first layer play an important role on the sensitivity.Compared with the conventional PCF structure,the sensitivity can be improved remarkably via employing large air holes with the shape of a combination of half circle and half oval.
2010, 59 (7): 4738-4747.
doi:10.7498/aps.59.4738
Abstract +
The conventional acoustic holography method is not suitable for the measurement of the moving sound source, because the Doppler effect exists in the sound signal, and the beam-forming approach is unable to make quantitative analysis. The approach proposed in this paper establishes the time-space relation between the measurement field, the radiating field and the acoustic holography field, and puts forward a method of nonlinear time-mapping between the sound source and the measured signal. Based on the acoustic source eigen-function, the acoustic pressure distribution of the acoustic holography field in the time domain is obtained, in which the Doppler effect is eliminated. The sound field of the surface of the moving sound source is reconstructed by acoustic holography method, and the quantitative analysis of the major sound source is realized. This method has been used in the experiment of measuring the moving sound sources, and satisfactory results proved the effectiveness of the method.
2010, 59 (7): 4748-4755.
doi:10.7498/aps.59.4748
Abstract +
This study has two main objectives: (1) to examine the availability of a filtering scheme developed by Mi et al (2005, Phys. Rev. E 71, 066304) on the measured velocity signal and (2) to investigate the centerline characteristic scales of a plane jet with the exit Reynolds number of Re = 13188. The success of the filtering scheme has been well validated. It is found that the existence of the high-frequency noise impairs not only the small-scale properties of turbulence but also those associated with large-scale turbulence. After filtering the noise, while the dissipation rate of turbulence kinetic energy is correctly obtained, the characteristic scales of turbulent flow (i.e. the Kolmogorov and Taylor turbulence micro-scales and the integral scale) are appropriately estimated. The results reveal that the centerline characteristic scales of the plane jet exhibit a linear dependence on the downstream distance (x) at x ≤ 20 h, where h is the height of the nozzle. It is interesting to note that the statistical properties of small-scale turbulence appear to enter their self-preserving state earlier than those of large-scale turbulence in the jet. To our knowledge, this finding has not been reported in the literature.
2010, 59 (7): 4756-4760.
doi:10.7498/aps.59.4756
Abstract +
For the barotropic fluid, based on the quasi-geostrophic potential vorticity equation, an inhomogeneous Boussinesq equation including topographic forcing and an external source is derived by employing the perturbation method and stretching transform of time and space. Through inspection of the evolution of the amplitude of the Rossby wave, it is found that Coridis effect, topography effect and an external source are the key inducing factors of the solitary Rossby wave if the basic stream function has a shear flow. Assuming that there is a balance between nonlinear and topography effects, an inhomogeneous Boussinesq equation is derived. The results show that the topography and the Rossby wave interact in the barotropic flow. The inhomogeneous Boussinesq equation describing the evolution of the amplitude of solitary Rossby waves with the change of Rossby parameter β(y) with latitude β, topographic forcing and the external source is obtained.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (7): 4761-4766.
doi:10.7498/aps.59.4761
Abstract +
To solve the method of measuring the viscosity of related substance at high pressures and high temperatures, Sakharov has proposed an experimental method of small disturbance in shock wave. However, the quantitative relation between the disturbance amplitude damping and viscosity in Sakharov flow field has not been given by theory. In this paper, the propagation of complex flow in Al, the development of relative disturbance amplitude on sinusoidal shock front, and the effect of viscosity on it are studied, and the relation between the relative distance of zero-point on the disturbance amplitude damping curve and viscosity is given. Compared with Zaidel’s uniform flow model and Millers’ nonuniform flow model, our Sakharov flow is close to real experiment. From our numerical analysis method, Sakharov small disturbance experiment can give a credible viscosity coefficient. We analyze the experimental data of Mineev again, and find the effective viscosity coefficient of Al at shock pressure 31 GPa and strain rate 2×106 s-1 should be modified by 1100 Pa·s, which is half of the former analytic result.
2010, 59 (7): 4767-4773.
doi:10.7498/aps.59.4767
Abstract +
There is a "pit" phenomenon in the target surface when long pulse laser ablates the foil target and speeds up the material of target. Laboratorty diagnosis and theoretical simulation of the pit can help us understand the relevant physical processes and check relevant parameters of the procedures. We use 13.9 nm Ni-like Ag X-ray laser as a probe to diagnose the plasma and the pit phenomenon, which is produced by 2ω nanosecond laser irradiation of C8H8 foil target. XRL2D code is used to simulate the experiments. Results show that, when the limiting factor of electron thermal transmittance is 0.03, the simulated pit width and depth (the distance of thin foil accelerated)agree with the results of experiment, but the foil thickening phenomenon in the area far away from the focal spot region cannot be explained the simulation.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (7): 4774-4780.
doi:10.7498/aps.59.4774
Abstract +
Mn-doped SiC magnetic thin films prepared by co-deposited molecular beam epitaxy (MBE) method on Si (111) substrates at 950 ℃ have been investigated by reflection high energy diffraction (RHEED), X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) techniques. RHEED results reveal that the SiC thin films doped with Mn are of the cubic structure. XRD and XANES results show that in the thin films with Mn doping concentrations of 0.5％ and 18％ , almost all the Mn atoms react with Si atoms, forming Mn4Si7 compound embedded in the SiC matrix, and no substitutional or interstitial Mn atoms exist in the SiC lattice. Furthermore, we hold that the ferromagnetism of the Mn doped SiC thin films originates mainly from the Mn4Si7 secondary phase.
2010, 59 (7): 4781-4787.
doi:10.7498/aps.59.4781
Abstract +
The construction of metallic nanocrystalline (NC) samples by molecular dynamics simulation is investigated. Firstly, the initial NC aluminum and copper samples are assembled by Voronoi geometrical construction method, then the local minimized energy states of the samples are obtained by quenching (or conjugate gradient method). Finally, the simulated annealing method in normal pressure and temperature condition ensembles at zero pressure is used to approximate the global minimized energy states of the samples. The residual internal stress is employed to signify the difference between the simulated and the experimentally synthesized samples for the first time. The structure of grain boundaries, the descending process and the local distribution of the average internal stress and the energy of the samples, as well as the elastic constants of the final samples are observed during these two relaxation procedures. It is found that the energy and the residual internal stress of the samples are close to the experimental data after relaxation. It is enough to obtain the global minimum energy states through Voronoi geometrical construction to investigate the static and dynamic mechanical properties of NC metals with a 5—10 ps local energy minimization and a 40—100 ps of simulated annealing with annealing temperature between the room temperature and 65% of melting point. The annealing time and temperature are of little importantce to the mechanical properties within the parameter windows properly selected.
2010, 59 (7): 4788-4793.
doi:10.7498/aps.59.4788
Abstract +
The doping effects of the boron (nitrogen, fluorine) are investigated in TiO2 nanoparticles by means of X-ray diffraction (XRD), Raman and UV-Vis absorption spectroscopy. No phase change due to B (N, F)-doping in anatase-TiO2 nanoparticle was found, while significant lattice contraction and enhanced lattice distortion (large c/a-value) were observed in B (N, F)-doped TiO2 nanoparticles, which has been attributed to the occupation of the surface oxygen vacancies by B (N, F) dopants along c-axis of TiO2 crystal lattice. In addition, the absorption band shows evident red-shift for B (N, F)-doped TiO2, which may be related to the increase of lattice distortion (c/a-value) in TiO2 nanoparticles.
2010, 59 (7): 4794-4801.
doi:10.7498/aps.59.4794
Abstract +
The Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers were prepared using sol-gel process combined with electrospinning. The thermal decomposition and phase inversion process of precursor nanofibers and the effects of calcination temperature and SiO2 content on the phase composition, microstructure, morphology and magnetic property of the resulting nanofibers were studied by means of thermogravimetric and differential thermal analysis, X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and vibrating sample magnetometer. The experimental results show that the cubic spinel structure is basically formed when the precursor nanofibers are calcined at 450 ℃ for 2 h. The average grain size of Ni0.5Zn0.5Fe2O4 contained in the composite nanofibers with 10 % SiO2 and their specific saturation magnetization and coercivity increase with increasing calcination temperature. Amorphous SiO2 additive can effectively restrain the growth of Ni0.5Zn0.5Fe2O4 nanocrystals. As a result, with SiO2 content increasing from 0 to 20 % , the average grain size of Ni0.5Zn0.5Fe2O4 in the prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers calcined at 900 ℃ for 2 h decreases from 81.6 to 13.3 nm, and the specific saturation magnetization of these samples monotonically decreases, whereas the coercivity initially increases and then decreases due to the change of magnetic domain structure from multi-domain to single-domain along with the reduction in grain size. In addition, with the increase of SiO2 content, the diameter of the as-prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers gradually increases and the surface becomes smooth.
2010, 59 (7): 4802-4807.
doi:10.7498/aps.59.4802
Abstract +
In vacuum environment, the nano-crystalline silicon films were prepared by pulsed laser ablation at high temperature and room temperature respectively. The amorphous films prepared under normal temperature were thermal-annealed, which leads to crystallization. The morphology and compositon etc. of the samples were characterized by scanning electron microscopy, Raman scattering and X-ray diffraction. The results showed that the temperature threshold of Si nanoparticles formation was 700 ℃ and 850 ℃ respectively. The nucleation energy of the nanoparticles was obtained by quantitative calculation, and the reason of difference between the temperature threshold was discussed from the point of view of energy.
2010, 59 (7): 4808-4811.
doi:10.7498/aps.59.4808
Abstract +
An effective interatomic potential is crucial for molecular dynamics simulations. In this paper, a more effective optimization method for potential parameters is proposed. Sensitivity analysis is used to find the key parameters affecting the structure and properties most in all the potential parameters. The secondary parameters are ignored, and the dimension of the optimization is reduced. The genetic algorithm is adopted to optimize the key parameters. The results show that the structure and physical properties of BaTiO3 and SrTiO3 simulated by the optimized potential are more close to experimental data.
2010, 59 (7): 4812-4817.
doi:10.7498/aps.59.4812
Abstract +
Lead tungstate (PbWO4, shorten as PWO) crystal has attracted much interest as a very dense, fast and radiation hard scintillator. However, its application is strongly hampered by its poor light output. At present, great efforts have been devoted to improve the scintillating efficiency of PWO crystals. In this paper, fluorine anions were used as dopant to improve the light output of PWO crystals. The crystals were grown by modified Bridgman method. The charge was obtained from PbO and WO3 powder with purity of 99.99% and 99.999% respectively. The transmittance spectra measured with a spectrophotometer Shimadzu UV-2501PC reveal that the transmission of PWO:F is much higher than that of undoped PWO, especially in the short wavelength region (330—500 nm). The most significant characteristic of the F-doped PWO is that two emission components can be identified in their photoluminescence spectra, a fast component related to the blue emission (419 nm) and a slow component related to the green emission (553 nm). The measured light yield of PWO:F, based on the pulse height spectra stimulated by 137Cs, is as high as 2 to 3 times of the undoped PWO and meanwhile will be increased with the integration of time gate. This means that the significant contribution to the light yield of PWO may come from the green luminescence. The decay constants excited by 22Na gamma ray can be fitted into three components, they are τ1=2.68[57.5%] , τ2=47.6[31.0%] and τ3=183[11.5%]. 88.5% of total scintillating light decays within 50 ns. However, the distribution of light yield along the crystal axis is not uniform, i.e. higher at the tail end than that in the seed end. It is suggested that the blue emission is ascribed to the regular lattice centers, namely [WO4]2- and the green one to a defect [WO3+F] cluster. The significant defects in PWO lattice induced by F-anion should be responsible for the increase of the light yield.
2010, 59 (7): 4818-4825.
doi:10.7498/aps.59.4818
Abstract +
Plutonium is vulnerable to aging due to α radioactive decay. The properties and behaviors of point defects in plutonium are the basis for understanding plutonium aging. We have employed a molecular dynamics technique to calculate the formation energy and binding energy of point defects and small helium-vacancy clusters in plutonium, using embedded atom method, Morse pair potential and the Lennard-Jones pair potential for describing the interactions of Pu-Pu, Pu-He and He-He, respectively. A single self-interstitial atom’s steady configuration is 〈100〉 dumb-bell. An interstitial helium atom at octahedral site is more stable than that at tetrahedral site. As a result of high binding energy of an interstitial helium atom to a vacancy, helium atoms can combine with vacancies to form helium-vacancy cluster during the process of self-radiation. The formation energy of helium-vacancy cluster increases with the increasing number of helium atoms. When the number of helium atoms equals to the number of vacancy, the helium-vacancy cluster is rather stable. Both substitutional and interstitial helium atoms are trapped at the grain boundary (GB). The binding energy of the self-interstitial atom at GB core is higher than that of helium atom and vacancy.
2010, 59 (7): 4826-4830.
doi:10.7498/aps.59.4826
Abstract +
The interaction between high power ion beam and the double-layer target system consisting of Ti film and Al substrate was simulated by TRIM Code. The evolution of energy distribution in the double-layer target irradiated by high power ion beam (HPIB) was obtained. Using the deposited energy in the target as the thermal source term in the nonlinear thermal conduction equations, finite differential method was used to solve the equations. And one-dimensional spatial and temporal evolution of the temperature of the Ti/Al double-layer target irradiated by HPIB during a pulse was obtained. The effect of the ion beam current density on the phase state of the film substrate interface was analyzed. The results show that both Ti and Al are melted at the interface when the ion beam current density is between 100 and 200 A·cm-2.
2010, 59 (7): 4831-4836.
doi:10.7498/aps.59.4831
Abstract +
ZnO thin films were implanted at room temperature with 80 keV N+ or 400 keV Xe+ ions. The implantation fluences of N+ and Xe+ ranged from 5.0×1014 to 1.0×1017/cm2, and from 2.0×1014 to 5.0×1015/cm2, respectively. The samples were analyzed using Raman spectroscopy and the Raman scattering modes of the N- and Xe-ion implanted samples varying with implantation fluences were investigated. It was found that Raman peaks (bands) at 130 and 578 cm-1 appeared in the spectra of ion-implanted ZnO samples, which are independent of the ion species, whereas a new peak at 274 cm-1 was found only in N-ion implanted samples, and Raman band at 470 cm-1 was found clearly in Xe-ion implanted samples. The relative intensity (peak area) increased with the increasing of the implantation fluences. From the comparison of the Raman spectra of N- and Xe-ion implanted ZnO samples and considering the damage induced by the ions, we analyzed the origin of the observed new Raman peaks (bands) and discussed the structure changes of ZnO films induced by N- and Xe-ion implantations.
EDITOR'S SUGGESTION
2010, 59 (7): 4837-4842.
doi:10.7498/aps.59.4837
Abstract +
The optimization of wire size has become a key technology for improving the chip system performance. Based on the influence of the wire size of interconnects on the delay, power, area and bandwidth, we propose an idea of optimal wire size based on multi-objective optimization method and obtain a multi-objective constrained analytical model by curve-fitting approach. The Hspice verification shows that the analytical model presented in this paper has a high precision and the average error is less than 5%. The algorithm is simple and can effectively compensate for deficiencies in application of quality factor approach and it can be applied to computer-aided design of nano-scale complementary metal-oxide semiconductor (CMOS) system chips.
2010, 59 (7): 4843-4848.
doi:10.7498/aps.59.4843
Abstract +
The prospects of Si-based optical emitting materials are optimistic because the materials are compatible with silicon microelectronics technology. Therefore, many experimental and theoretical studies are directed to the design of direct band-gap Si-based materials. Based on the core state effect, the electronegativity differences effect of component atoms and the symmetry effect, Si-based superlattices Si1－xSnx/Si were designed. We found that Si0.875Sn0.125/Si is a direct band-gap material. In the density functional theory frame, the results of plane pesupotential method show that Si0.875Sn0.125/Si is a direct band-gap superlattice with minimum band-gap at Γ point. We predict that the band gap of the material is 0.96 eV with the help of GW approximation method.
EDITOR'S SUGGESTION
2010, 59 (7): 4849-4856.
doi:10.7498/aps.59.4849
Abstract +
The compressive behavior is one of the most basic mechanical properties of engineering materials. With the simplified structural model, the compressive failure mode is analyzed for isotropic three-dimensional reticulated porous materials, and the mathematical relationships between nominal main stress and porosity are obtained for these materials at shearing failure under uniaxial compression, biaxial compression and triaxial compression, respectively. The results show that, the porous body of brittle material species shows the tensile fracture mode of pore struts, and the porous body of ductile material species may display the shearing fracture mode of pore struts. The correspondingly obtained criteria of strength design can be referred to in applications of these materials under respective loading failure modes.
2010, 59 (7): 4857-4862.
doi:10.7498/aps.59.4857
Abstract +
The influence of phonon and megnetic field on property of polaron in quantum ring was studied by solving precisely the energy eigen-equation, unitary transformation and variational method. The numerical calculation for KBr quantum ring showed that the ground state energy of electron or polaron increases with increasing frequency (or the averaging radius) of the quantum ring, the polaron energy shift decreases with increasing frequency (or decreasing averaging radius) of the quantum ring, and the mean phonon number increases with increasing frequency (or decreasing averaging radius) of the quantum ring. When a perpendicular magnetic field is present, the energy levels of the polaron may cross, the ground state changes from the state with m=0 to that with m=-1,-2,-3,…, and the ground state energy makes non-periodical oscillation with increasing magnetic field strength; the polaron energy shift decreases with increasing magnetic field strength (or absolute value of quantum number |m|).
2010, 59 (7): 4863-4873.
doi:10.7498/aps.59.4863
Abstract +
Firstly, some results about the frequencies of phonons in wurtzite ternary mixed crystals (TMCs) fitted by several methods (modified random-element-isodiplacement model (MREI), virtual crystal approximation, and simplified coherent potential approximation, etc.) are compared. Then, combined with the continuous dielectric model and uniaxial crystal model, a fitting method available to experimental data is adopted to derive the dispersion relations of different kinds of optical phonon modes in TMC InxGa1－xN and AlxGa1－xN quantum wells. Furthermore, the variation of phonon modes dependent on the composition is analyzed. The results show that the fitting by the MREI for phonon frequencies of wurtzite TMCs with one-mode property agrees better with the experimental data. It can be also found that the optical phonon modes in quantum wells vary with the composition. The phonon modes, such as localized modes, interface modes, half-space modes, and propagating modes, exist in certain composition regions and frequency regions due to the anisotropy of phonon dispersion of wurtzite nitrides. Moreover, the shape of the same kind of phonon modes also varies with the composition.
2010, 59 (7): 4874-4879.
doi:10.7498/aps.59.4874
Abstract +
With a real-space renormalization-group method, the anisotropic quantum Heisenberg model on three-dimensional diamond-type hierarchical lattice is studied, and the phase diagram and critical properties are obtained. For the ferromagnetic system, it is shown that there is a finite-temperature phase transition for Δ=0 where Δ is the anisotropy parameter. The order parameter and critical exponents are also calculated. For the antiferromagnetic model, we find that the critical temperature is not equal to zero for Δ=0 and there is not reentrant behavior on the critical line.
2010, 59 (7): 4880-4887.
doi:10.7498/aps.59.4880
Abstract +
The thermodynamic properties, structure, and dynamic properties of ethanol from ambient conditions to supercritical states were investigated by molecular dynamics simulation (MD). With the increase of temperature, the enthalpy and self-diffusion coefficients increase, while the hydrogen bonding interaction between ethanol molecules weakens. With the increase of pressure, the self-diffusion coefficients decrease, while the hydrogen bonding interaction increases. The self-diffusion coefficient of ethanol in supercritical region is 10 times greater than that in the liquid region. It changes slightly with temperature in the liquid region, while decreases rapidly with pressure in the gas region. The influence of density on self-diffusion coefficient could be manifested by the influence of temperature and pressure. Under supercritical conditions, the ethanol system shows aggregation phenomenon which is even more evident in the low-density region due to density fluctuations. The hydrogen bond of ethanol molecules significantly weakens, the structure becomes loose and the molecular polarity is greatly reduced in supercritical conditions compared with that in ambient conditions. Our results are in good agreement with the experimental data.
2010, 59 (7): 4888-4894.
doi:10.7498/aps.59.4888
Abstract +
The bcc—hcp structural transition in single crystal iron under 〈001〉 uniaxial strain has been investigated by molecular dynamics simulation. The reversibility and the morphological characteristics are discussed. The stress history indicates a super-elastic deformation in the sample, while the change of temperature shows the heat release during both hcp and bcc nucleation. A laminated structure of bcc and hcp along {011} planes is obtained, where the phase boundaries for the bcc to hcp and hcp to bcc transition are found along the same plane, implying the memory effect of morphology. Stacking faults (fcc) can be formed at the interface between hcp nuclei. For the bcc to hcp transition, we observed the mergence of the stacking faults in an hcp grain and the position adjustment between hcp grains. No migration of stacking fault is found during the hcp to bcc transition. In addition, the bcc—hcp transition structure is analyzed by the radial distribution function.
2010, 59 (7): 4895-4900.
doi:10.7498/aps.59.4895
Abstract +
With the integrated circuits processing stepping into nanometer scale, the interconnect Joule heat becomes significantly large. Based on the RLC π equivalent circuit, this paper proposes a novel accurate model to evaluate Joule heat power of interconnected line in VLSI. The shielding effect of the inductor and the non-ideal step stimulation are considered in the proposed model. The power consumption of a typical interconnected topology in 90 nm complementary metal-oxide semiconductor process is computed. The error between results of this proposed method and Hspice simulation is within 3% when the input signal’s delay time is within 1 ns. The proposed model can be used to estimate Joule heat consumption where rough heat control is needed, such as route structure in the network on chip.
2010, 59 (7): 4901-4910.
doi:10.7498/aps.59.4901
Abstract +
During the process of plasma enhanced chemical vapor deposition, the growth rate of microcrystalline silicon films must be improved to reduce manufacture cost. With the increase of growth rate, the photoelectrical properties of such films will be greatly decreased. The main cause is the diffusion length of the precursors on the film surface decreases. In this study, a quantitative kinetic model was developed and the reaction balance equations of SiH3 and H were constructed, and the deposition rate, diffusion length and their influencing factors were obtained. We find that the deposition rate is determined by the fluxes of both SiH3 and H. The diffusion length of precursors is determined by the substrate temperature and the configuration of the surface silicon-hydrogen bonds. The diffusion length has a higher value when the growing film surface is covered by mono-hydrides, it has a smaller value when covered by tri-hydride, and it has a value close to zero when covered by dangling bonds.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (7): 4911-4918.
doi:10.7498/aps.59.4911
Abstract +
Using the pseudopotential plane wave (PPPW) method, we performed first principles calculation for the multilayer relaxations and the electron properties of the high-Miller-index stepped Cu(311), (511), (331) and (221) surfaces, which are expressed by 2(100)×(111), 3(100)×(111), 3(111)×(111) and 4(111)×(111), respectively, in the terrace-step notation, i.e. n(hkl)×(uvw). The interlayer relaxations of them are -+-…, --+-…, --+-… and ---+-…, respectively, which follow the atom-row trend: for stepped Cu surface which has n atom rows in the (100) or (111) terrace, the outermost n－1 interlayer spaces contract, then the n interlayer space expands, and the following n+1 interlayer space contracts again. For the stepped surfaces with the same (hkl)×(uvw), the larger the number of atom rows n in the terrace, the greater the contraction magnitude for Δd1,n. We did not find any indication of anomalous relaxation behavior for Cu(511) and (331) as mentioned in some references. Below Fermi energy level, the density of states of the first layer atom at stepped edge has the largest peak value in higher energy regions and has no peak in lower energy regions, so the first layer atom is most unstable and can be dislodged and peeled off more easily than other surface atoms. For the stepped surfaces with the same (hkl)×(uvw), the curves of the density of states have similar shapes for the atoms at the step edge, at the corner, at the terrace and near the corner, and the atoms under the step edge and near the corner.
2010, 59 (7): 4919-4924.
doi:10.7498/aps.59.4919
Abstract +
With the first-principles density functional theory, based on ultra-soft psuedopotential method, the structure, elastic, and electronic structure properties of WC-type RexW1－xC(x=1, 0.25, 0.75, 0), Re0.5Os0.5C, and Os0.5W0.5C were studied. It was found that the shear modulus of Re0.25W0.75C is higher than that of all synthesized and theoretically predicted 5d transition metal carbides. An analysis of Mulliken population of the bond between transition metal and C atom shows that the large shear modulus of Re0.25W0.75C is mainly due to the strong covalent Re—C interaction. The low value of the density of states on the Fermi level indicates the high stability of Re0.25W0.75C. The excellent elastic property and high stability suggest that hexagonal Re0.5W0.5C can be an ultra-hard material. We hope our calculations can stimulate the experimental research to synthesize it.
2010, 59 (7): 4925-4929.
doi:10.7498/aps.59.4925
Abstract +
The band structure, total density of states and partial density of states of pure and In-doped wurtzite ZnO have been investigated by using the first-principles ultrasoft pseudo potential approach of the plane wave. The calculation indicates that the band gap of ZnO is reduced by In doping. The energies of both the conduction band minimum and the valence band maximum decrease with increasing In-doping concentration, but the decrease of the conduction band minimum is much more pronounced than that of the valence band maximum, which leads to narrowing of the band gap. Moreover, it was found that In-doping can cause increase of the lattice constant, which also reduces the band gap.
2010, 59 (7): 4930-4938.
doi:10.7498/aps.59.4930
Abstract +
The crystal structure, electronic structure and optical properties of nitrogen and iron codoped anatase TiO2 were studied by using the plane-wave ultrasoft pesudopotentials method based on density functional theory. The calculated results show that the octahedral dipole moments in nitrogen and iron codoped TiO2 increase due to the changes in lattice parameters, bond length and charge of atoms, which is very effective for the separation of photoexcited electron-hole pairs and the improvement of the photocatalytic activity of TiO2. Some impurity energy levels of codoped TiO2 are below the conduction band minimum, and others are above the valence band maximum. The distance between them is narrowed, which results in the redshift of the optical absorption edges to visible-light region. These impurity energy levels can reduce the recombination rate of photoexcited carriers and improve the photocatalytic efficiency of TiO2. Compared with that of Fe doped TiO2, for the codoped TiO2, the density of states peak of impurity energy levels above the valence band maximum increase apparently, which increases the electronic transition probability from the impurity energy levels to the conduction band, and improves the solar energy utilization. If the impurity level is not taken into account, compared with that of pure TiO2, the CB edge position and the VB edge position of codoped TiO2 is only slightly changed, it means that the strong redox capacity of codoping photocatalysts is still excellent.
2010, 59 (7): 4939-4944.
doi:10.7498/aps.59.4939
Abstract +
The electronic structure parameters of density of electronic states, atoms embedding energy, affinity energy and cluster energy of Nb alloy have been calculated using the recursive method. The high-temperature oxidation mechanism of Nb alloy was investigated. Studies show that the oxygen adsorption on Nb alloy surface can lower the adsorption energy, so oxygen is easily adsorbed on the alloy surface, and gradually diffuses into the Nb alloy matrix. Oxygen has a high solubility in the Nb alloy matrix because of the negative atom embedding energy, and it has similar density of states to Nb. Because the atom embedding energies of Ti and Al in the alloy matrix are higher than that on the alloy surface, Ti and Al atoms diffuse from the alloy matrix to the alloy surface and segregate on the alloy surface, ultimately making the Nb surface rich in Ti and Al. The clustering energy calculation shows that Ti and Al atom tend to gather on their own area, forming Ti and Al atom clusters respectively. Oxygen can interact with Nb, Ti and Al because of the negative affinity energy with Nb, Ti and Al on Nb alloy surface, to generate the Nb2O5, TiO2 and Al2O3 mixed oxide film which has protective effect on Nb alloy.
2010, 59 (7): 4945-4949.
doi:10.7498/aps.59.4945
Abstract +
The electronic structure and optical properties of UO2 are investigated using the first principles density functional method within local-spin density approximation (LSDA), and the Coulomb correlation energy (U) is used to calculate the lattice constant, energy band structure and optical properties of UO2. The calculated lattice constant is 5.40 ?, and the band gap is 1.82 eV. We succeeded in predicting the correct anti-ferromagnetic insulating ground state of uranium dioxide. By analyzing the energy structure and dielectric function, we find that in uranium ions the 6d band splits into two sub-bands, which is in agreement with experimental results.
2010, 59 (7): 4950-4954.
doi:10.7498/aps.59.4950
Abstract +
The structural stability and electronic field emission properties of carbon nanotubes doped with a boron atom in different layers and adsorbed with several H2O molecules, as well as located in the applied electric field, are analyzed by means of the density functional theory based on the first-principles. The results show that the structure of B3CNT+5H2O doped by a boron atom in the third layer and adsorbed with five H2O molecules is most stable, the distribution of Mulliken charge on the tube cap is most dense. In particular, compared with the B3CNT doped by a boron atom and CNT+5H2O adsorbed with five H2O molecules solely, the density of states at the Fermi energy level for B3CNT+5H2O increases by 20% and 33% respectively. Therefore, the latter has the best field emission property.
2010, 59 (7): 4955-4960.
doi:10.7498/aps.59.4955
Abstract +
The first principle based on the density functional theory and nonequilibrium Green's function method is adopted to study the energy level, the electronic structure and the electronic conductance of C32 molecular devices in which Au(1,1,1) electrodes are a ttached to the two farthest carbon atoms when different distances between electrodes and the central molecule are considered. The electronic transmission spectrum and I-V curves of the molecular devices at different distances are obtained. The reasons leading to the electronic structure and the electronic transmission characteristics are analysed. The impacts of the distance between Au electrodes and the central molecule and the gate-voltage on the electronic transmission are discussed. The results show that the distance between the central molecule and Au electrodes has greater influence on the electronic transmission characteristics. The results also show that the C32 molecule has obvious semiconductor characteristics.
2010, 59 (7): 4961-4966.
doi:10.7498/aps.59.4961
Abstract +
By LLP(Lee-Low-Pines)-like transformation and fractional-dimension variational treatment, the ground-state energies of excitons confined in Ga1－xAlxAs/GaAs/Ga0.7Al0.3As asymmetric square quantum well and the influence of phonons are demonstrated. The exciton ground-state energy has a minimum value with the increasing well width. And we make clear the effects of the barrier height on the fractional dimension, exciton ground energy and binding energy. After taking into account of the interaction of exciton with LO-phonons, the values of the exciton ground-state energies increase remarkablely. Moreover, the exciton binding energy increases as the asymmetric well-width decreases or the barrier height increases.
2010, 59 (7): 4967-4971.
doi:10.7498/aps.59.4967
Abstract +
A method for measuring the ultraviolet spectrum characteristic of Au photocathode has been put forward. Making use of the high gain characteristic of microchannel plate (MCP) and ultraviolet light, the frequency response of Au cathode has been studied by measuring the output current of Au coated MCP detector directly. Through measuring the response current of Au coated MCP detector between 200—340 nm, the selective photoemission of Au has been found, which had been found only for alkali metals. And the selective peak is at 5.72 eV, which can be explained by quantum mechanics theory.
2010, 59 (7): 4972-4979.
doi:10.7498/aps.59.4972
Abstract +
Based on a tight-binding disordered model describing a single electron band, a model of quasi-one-dimensional disordered systems with several chainsis established, and the direct current (dc) and alternating current (ac) conductance formula are obtained. By calculation, the dependence of the dc and ac conductivity on the disorder mode, dimension, temperature, and electric field is studied. The results indicate that the dc and ac conductivity of the systems decreases with the increase of the degree of lattices energy disorder, while the off-diagonal disorder can enhance the electrical conductivity of the system. Meanwhile, the conductivity increases with the increase of the number of chains in the systems. The model also quantitatively explains the temperature and electric field dependence of the conductivity of the system, that is, in diagonal disordered systems, the ac conductivity of the systems increases with the increasing of temperature, in off-diagonal disordered systems, the ac conductivity of the systems decreases with the increasing of temperature, while the dc conductivity of the systems in all disordered modes increases with the increasing of temperature. In addition, the dc conductivity of the quasi-one-dimensional disordered systems increases with the increasing of the strength of dc electric field, showing the non-Ohm’s law conductivity characteristics, and the larger the number of chains in systemis, the more slowly the dc conductivity of systems increases with the increasing electric field. The ac conductivity quasi-one-dimensional disordered systems increases as the frequency of the external electric field rises, satisfying the relation σac(ω)∝ω2[In(1/ω)]2.
2010, 59 (7): 4980-4984.
doi:10.7498/aps.59.4980
Abstract +
We investigate theoretically the intense terahertz field-driven electron-transport through a nonmagnetic semiconductor-heterostructure with spin-orbit coupling. It is found that the frequency-dependent conductivity spectra possess splitting resonance-peaks of asymmetric Fano-type, and multiple-photon-process arises with the increasing amplitude of oscillating field. By changing the external field parameters, the purpose of spin filtering may be realized, and 100% pure spin-polarized current at the frequency of Fano-resonance can also be achieved. These interesting features may be a very useful basis for devising a wide range tunable spin filter and realizing pure spin current.
2010, 59 (7): 4985-4988.
doi:10.7498/aps.59.4985
Abstract +
The transport properties and I-V characteristics of boron-carbon and boron-nitride quantum dot devices are investigated by first principles method. The results of the B-C and B-N devices consisting of the same number of atoms have significant differences. There is large density of states near the Fermi energy for B-C device. A wide gap in the density of states of B-N device exists and the Fermi energy lies in the gap. The B-C device reveals metal property and the B-N devices appear as semiconductors.
2010, 59 (7): 4989-4995.
doi:10.7498/aps.59.4989
Abstract +
Using Crosslight APSYS software, we study the effect of the electrode shapes on the electrical and optical properties for the chip structures of p-GaN, InGaN/InGaN multiple quantum well, n-GaN and sapphire. Six kinds of optimized electrodes are presented. By optimzing the electrode shape, the current density distribution are more uniform, and the current crowding effects are reduced. And for the chips with optimized electrodes their electrical and optical properties are improved, and the light emission efficiencies and transferring efficiencies have been also improved.
2010, 59 (7): 4996-5001.
doi:10.7498/aps.59.4996
Abstract +
InGaN/GaN triangular shaped multiple quantum wells (MQWs) grown on sapphire substrate were adopted as an active layer of light-emitting diodes (LEDs) by modulating In content in well layers. The temperature dependence of the normalized integrated photoluminescence (PL) intensity showed that the overlap of the electron and hole wave-functions of the LEDs with triangular shaped MQW is much higher than that of the LEDs with conventional rectangular MQW structures, which improves the internal quantum efficiency (IQE) to a certain degree. On the other hand, it was found that the blue shift of the peak energy as a function of injection current is improved for the device with triangular shaped MQW structure from the electroluminescence (EL) spectra of the two series devices. The comparison above indicates that the triangular MQW LEDs are more efficient and more stable.
2010, 59 (7): 5002-5009.
doi:10.7498/aps.59.5002
Abstract +
Accelerated aging and life-time tests at ambient temperatures of 40 ℃,70 ℃ and room temperature were carried out on GaN-based white light-emitting diodes (LEDs). The electrical, optical and thermal characteristics of the device were compared before and after different aging times in order to investigate the failure mechanism of the device. Here, we mainly analyzed the failure mechanism related with the chip and the phosphor of the LED. The current-voltage characteristics demonstrated that both the series resistance and the tunnel current increase under lower forward voltages after aging, which were due to the degradation of p-type ohmic contact and the increase of defect density. The thermal characteristics confirmed that the thermal resistance increased rapidly under high aging temperature. This was mainly attributed to the fracture of different materials inside the devices caused by the difference in thermal expansion coefficients. Optical measurements indicated that high aging temperature could accelerate the degradation of output power and reduce the conversion efficiency of the phosphor as well. Finally, the life time of the device was calculated using Arrhenius-equation, and the failure mechanism was analyzed.
2010, 59 (7): 5010-5017.
doi:10.7498/aps.59.5010
Abstract +
Due to carrier band-to-band tunneling (BTBT) through channel-source/drain contacts, traditional MOS(metal oxide semiconductor)-like carbon nanotube field effect transistors (CNFETs) suffer from quasi-ambipolar transport property, leaving much negative impacts on device performance and its application in circuits. To suppress such quasi-ambipolar behavior, a novel device design based on dual-gate-material device structure is proposed. The modeling results show that, with proper choice of tuning gate material, this device design can increase the ON-OFF current ratio by 6—9 orders of magnitude, tune the threshold region effectively and keep the sub-threshold slope immune from it. In addition, the quasi-ambipolar transport characteristic of C-CNFETs can be suppressed effectively using such novel device design. Further study reveals that the performance of the proposed design depends highly on the choice of tuning gate material, and the quantum capacitance in CNFETs has great effect on not only its subthreshold slope but also its transport polarity.
2010, 59 (7): 5018-5022.
doi:10.7498/aps.59.5018
Abstract +
Indium oxide thin film was deposited on glass substrate by radio frequency magnetron sputtering at room temperature. The In2O3 film was polycrystalline with a preferred (111) orientation and a grain size of 33 nm was estimated. The bottom-gate staggered thin film transistors (TFTs) were fabricated by standard photolithography, with In2O3 as active channel layers. The In2O3 TFTs exhibit good gate bias controlling characteristic with a field effect mobility of 6.3 cm2/V·s, an on-off current ratio of 3×103, and a threshold voltage of -0.9 V. Device performance and room temperature fabrication technology make In2O3 TFTs promising for display panel applications.
2010, 59 (7): 5023-5027.
doi:10.7498/aps.59.5023
Abstract +
A thick-screen frequency selective surface (FSS) with circle slot elements is designed. Based on the moment method simulation, we investigate mainly the transmission properties of this structure under no dielectric condition, when some parameters, including the element diameter, unit distribution period and incidence angle of electromagnetic wave,are changed. The result of numerical analysis show that the unit diameter, unit spacing and incidence angle have great influence on the transmission properties of the thick-screen FSS,but unit diameter has little influence on the center frequency.
2010, 59 (7): 5028-5034.
doi:10.7498/aps.59.5028
Abstract +
Three new kinds of liquid source were prepared by mixing R2O3 (here R is Gd,Y or Yb respectively),BaCuO2 and CuO powders. Single-domain Gd-Ba-Cu-O bulk superconductors have been fabricated using these liquid sources by the top seeded infiltration and growth technique. The growth characteristic and microstructure of the samples have also been investigated in detail. The results indicate that, employment of the new liquid sources not only can help us reduce the experimental period and improve the fabrication efficiency, but also can be used to fabricate well-textured single domains. Additionally, using the liquid source mixed by Y2O3 or Yb2O3 can raise the utilization rate of the liquid source powders, as well as contribute to the refinement of Gd-211 particles in the molten liquid.
2010, 59 (7): 5035-5043.
doi:10.7498/aps.59.5035
Abstract +
High quality large area Tl2Ba2CaCu2O8(Tl-2212)superconducting thin films were fabricated on CeO2 buffered two-side sapphire substrates. Using metallic cerium target as the sputtering source, CeO2 buffer film with c-axis orientation was deposited by radio frequency reactive magnetron sputtering, and the influence of preparation conditions on the structure and surface morphology of the CeO2 layer was studied. The Tl-2212 superconducting thin film was fabricated on CeO2 buffered sapphire substrate by direct current magnetron sputtering and post annealing. Scanning electron microscope showed that the film has a compact microstructure with uniform flat surface. The X-ray diffraction indicated that the film was pure Tl-2212 phase with c-axis perpendicular to the substrate surface, and epitaxially grown on the CeO2 buffered sapphire. The superconducting film exhibited excellent uniform electric properties. The critical transition temperature Tc was around 105 K, the critical current density Jc(77 K, 0 T) was around (1.2±0.1) MA/cm2 and (1.25±0.1) MA/cm2, respectively, and the microwave surface resistance Rs (77 K, 10 GHz ) of the film was as low as 390 μΩ.
2010, 59 (7): 5044-5048.
doi:10.7498/aps.59.5044
Abstract +
At present, the high-transition-temperature radio frequency superconducting quantum interference device (High- T c RF SQUID) is usually coupled to a dielectric resonator which is a standard 10 mm×10 mm× 1 mm SrTiO3 (STO) substrate with a YBa2Cu3O7-δ (YBCO) thin-film flux focuser deposited on it. The dielectric resonator for the High- Tc RF SQUID has a high quality factor and a resonant frequency in the microwave range. In order to find out the effect of the flux focuser’s geometry on the dielectric resonator’s resonant frequency, we used ANSOFT high frequency structure simulator (ANSOFT HFSS) to simulate the resonance characteristics of some dielectric resonators with different flux focuser geometries. Our simulation results show that when the width of the flux focuser’s slit increases or the radius of the flux focuser’s inner hole decreases, the dielectric resonator’s resonant frequency increases. To estimate the reliability of our simulation results, we selectively prepared a few dielectric resonators and measured their resonance characteristics. The experimental results are virtually consistent with the simulation results. Our study shows that changing the flux focuser geometry is an effective way to adjust the dielectric resonator’s resonant frequency.
2010, 59 (7): 5049-5054.
doi:10.7498/aps.59.5049
Abstract +
The existing experimental results have shown that the magnetic characteristics of amorphous wires with different lengths or of the same amorphous wire at different longitudinal locations are significantly different. To study this effect, the magnetic field at the end of the amorphous wires is obtained by numerical computation method based on the supposed uniform distribution of the magnetic charge. Then, the general formula of the magnetic field inside the amorphous wire is deduced by analyzing the calculation results and using the fitting algorithm. Because the magnetic field intensity inside the wire is restricted by the external magnetic field source, the model of three magnetic zones is proposed, which consists of the zone of uniform magnetic field in the middle of the wire, the magnetic field entrance-zone and exit-zone at the two ends. The critical length of the magnetic end effect can be estimated by a formula derived from the model. The simulation results of the magnetic end effect can satisfactorily explain the existing experiments.
2010, 59 (7): 5055-5060.
doi:10.7498/aps.59.5055
Abstract +
The bilayered magnetoelectric composite model has been analyzed. The non-homogeneous partial differential equation of the magnetoelectric material interacting with the microwave has been obtained in the condition that the partial derivative of the microwave is non-zero along the transmitting direction when the size of the magnetoelectric material is comparable with the wavelength. The analytic solution is solved for the equation at resonant condition, and then the analytic expressions of the magnetoelectric coefficient and the equivalent electric parameters are calculated. The results show that there is a correlative coupling term in excess in the magnetoelectric coefficient,the magnitude of which is related not only to the material parameters, but also to the microwave’s velocity in the material, and the equivalent admittance is related to the microwave’s frequency.
2010, 59 (7): 5061-5066.
doi:10.7498/aps.59.5061
Abstract +
A hard template process for preparing piezoelectret films with ordered void structure was described. By using the fabrication process, fluorocarbon polymer piezoelectret film was prepared. The scanning electron microscope (SEM) images showed that the fluorocarbon polymer film piezoelectret has very regular void structure as expected. The piezoelectricity of the fluorocarbon polymer film was investigated by measuring the quasi-static piezoelectric d33 coefficient using positive piezoelectric effect. The thermal stability of d33 was studied by taking the measurement of d33 decay at elevated isothermal temperatures. The results showed that a piezoelectric d33 coefficient of 300 pC/N was achieved. Compared with the fluorocarbon polymer film with disordered void structure, the film with ordered void structure has much improved thermal stability of d33, which can be further improved by pre-ageing treatment. The piezoelectric d33 coefficient is dependent on the applied pressure considerably in the range of 2—35 kPa, which is probably associated with the enhancement of Young’s modulus of the film with the increasing pressure.
2010, 59 (7): 5067-5072.
doi:10.7498/aps.59.5067
Abstract +
The distribution of trap levels in the low density polyethylene (LDPE) was studied by means of photo-stimulated discharge (PSD). And two scanning modes, continuous scanning and step scanning, were discussed. It was pointed out that there may be some problems because of the incomplete detrapping of the trapping charges for the continuous scanning. The principle and the experimental process for the step scanning were presented. It is found that there is a linear relationship between the logarithm of PSD current produced under the irradiation of the monochromatic light and the time, which is in accordance with the theoretical analysis and indicates that the retrapping effect of the carriers can be neglected. The charges are trapped in the levels of 4.36—6.22 eV in LDPE, the main part of which were trapped in the energy levels of 4.78—5.18 eV.
2010, 59 (7): 5073-5077.
doi:10.7498/aps.59.5073
Abstract +
Plane wave expansion method is applied to simulate the bandgap of two-dimensional photonic crystals made of a triangular lattice of dielectric rods(circular,hexagon,square cross sections) in air. Moreover, the effect on band gap of a triangular lattice of square dielectric rods in air is discussed as a function of the rotation angle, the refractive index and the filling fraction, respectively. In the low frequency region, the maximum complete photonic band gap appears when the rotation angle equals 17 degrees. the maximum complete photonic band gap can be attained steadily as the refractive index changes continuously. In the high frequency region, the maximum complete photonic band gap appears when the rotation angle equals 30 degrees. The complete photonic band gap is observed when the refractive index is greater than 2.2. The width of complete photonic band gap reaches the maximum when the dielectric refractive index is equal to 2.6.
2010, 59 (7): 5078-5084.
doi:10.7498/aps.59.5078
Abstract +
The spin ladder compounds Sr14Cu24O41+δ were synthesized by conventional solid state reaction method with subsequent annealing at 400, 500, 600, 800 and 900 ℃, respectively. The energy dispersive spectroscope (EDS) measurement confirms that the content of oxygen in the samples decreases with the increasing of annealing temperature. The measurement of magnetic susceptibility reveals that the sample annealing at 600 ℃ has the largest number of dimers. The measurement of Raman spectrum shows some new Raman vibrational features. Corresponding to δ>0 or δα=cl/cc is near the minimal value 10/7 and the Cu—O bond has relatively long length.
2010, 59 (7): 5085-5090.
doi:10.7498/aps.59.5085
Abstract +
Raman spectra of KTa1－xNbxO3(KTN) single crystal,its melt, and the solid-liquid boundary layer in the growing process at different temperatures were measured in-situ. The structure transformation in KTN crystal growth process was investigated. The results showed that the [Ta/NbO3] entities came into solid-liquid boundary layer from KTN melt, and they were transformed to [Ta/NbO6] octahedron entities. And the structure of [Ta/NbO6] octahedron entity was just like that of KTN single cell. Regarding [Ta/NbO6] octahedron as growth units, the growth habit of KTN crystal in which the (100), (1-00), (010) and (01-0) faces are easily revealed was discussed. The thickness of the growth solid-liquid boundary layer of KTN crystal was about 80—90 μm.
2010, 59 (7): 5091-5099.
doi:10.7498/aps.59.5091
Abstract +
The article reports the infrared quantum cutting phenomenon of the Er-doped nanophase oxyfluoride vitroceramics (Er(3):FOV). The infrared and visible fluorescence spectra of Er(3):FOV are measured carefully. It is found that the approximate quantum cutting efficiency of the 1543.0 nm 4I13/2→4I15/2 fluorescence, when the 2H11/2 levels are excited, is about 186.28%. The relative nonradiative relaxation rate and spontaneous emission rate and energy transfer rate are calculated. The relative energy transfer dynamics is analyzed. It is found that the {2H11/2→4I9/2, 4I15/2→4I13/2} energy transfer channel, with the rate of 371000 s-1, is the main reason for 2H11/2 energy level to have high quantum cutting efficiency. To our best knowledge, the present article for the first time reports Er(3):FOV to have an effective three-photon infrared quantum cutting excited by visible light and a four-photon infrared quantum cutting excited by near-violet light.
2010, 59 (7): 5100-5104.
doi:10.7498/aps.59.5100
Abstract +
Excited respectively by the light with wavelengths of 300, 400, 440 and 380 nm, the fluorescence spectra of synthetic food color ponceau 4R, amaranth, allurea red and industrial dye Sudan Ⅳ have been measured. For each sample, 60 emission wavelength values were selected. The fluorescence intensity corresponding to the selected wavelength was used as the network characteristic parameters, a probabilistic neural network for kind identification was trained and constructed. It was employed to identify the 32 kinds of color solution samples. Because the fluorescence spectra of these colors overlap, the identification rate is low. In order to solve this problem, a derivative fluorescence spectroscopy was introduced. The derivative fluorescence data was used as the network characteristic parameters, a probabilistic neural network was constructed and was employed to identify colors. The identification rate is up to 100%. Based on this, a new method is presented, which combines the derivative fluorescence spectroscopy and probabilistic neural network, and can identify synthetic colors easily, quickly and accurately. This method can provide support for food safety supervision and management.
2010, 59 (7): 5105-5109.
doi:10.7498/aps.59.5105
Abstract +
The simulation of a plasmonic very-small-aperture laser is demonstrated in this paper. It is an integration of the surface plasmon structure and very-small-aperture laser (VSAL). The numerical results demonstrate that the transmission field can be confined to a spot with subwavelength width in the far field (3.5 μm far from the emitting surface), and the output power density can be enhanced over 30 times of the normal VSAL. Such a device can be useful in the application of a high resolution far-field scanning optical microscope.
2010, 59 (7): 5110-5115.
doi:10.7498/aps.59.5110
Abstract +
The new phase grating based on two-dimensional structured thin films is reported. The rigorous coupled-wave analysis (RCWA) is employed to calculate the diffraction efficiency which varies with incident wavelength and angle. According to the result obtained by using RCWA, when the wavelength ranges from 600 to 640 nm, TE mode and TM mode can be diffracted in the transmitted 0th and ±1st orders, respectively, at normal incident angle. For example, at the wavelength of 633 nm, the polarization extinction ratio of 0th order is I0,TE/I0,TM=109.8, and the polarization extinction ratio of ±1st order is I±1,TM/I±1,TE =334.6. This polarizing beam splitting phenomenon is confirmed by theoretical simulation with finite-difference time-domain method, which shows that TE mode and TM mode can be separated by an angle of about 10°in glass substrate. The same simulation method is performed for the diffraction at incident angle of 23° in order to compare with the results from RCWA and grating equation calculation.
2010, 59 (7): 5116-5121.
doi:10.7498/aps.59.5116
Abstract +
Positron annihilation spectroscopy(PAS)and photoluminescence (PL) have been adopted to study defects in proton-irradiatied Zn-doped GaSb. A monovacancy VGa having a lifetime of 293 ps was observed in the non-irradiated sampls and a divacancy VGaVSb with a tifetime of 333 ps was identified in the proton-irradiated samples when the fluence reached 3×1015 cm-2.The PL results reveal that the acceptor Zn is not related with proton irradiation-induced defects, which act as non-radiation recombination centers in the samples. The acceptor level of Zn in GaSb has been calculated from the PL spectra. After proton irradiation, interstitial monatomic hydrogen in a negative charge state (Hi-) in GaSb has been found, which acts as a shallow-acceptor. Annealing experiments indicated that the as-grown and proton-irradiated samples have different annealing behaviors, the reason for which was attributed to the existence of monatomic hydrogen interstitials in the proton-irradiated samples.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (7): 5122-5127.
doi:10.7498/aps.59.5122
Abstract +
The micro subsurface cracks of fused silica etched with HF solution were recorded using atomic force microscope (AFM) and optical microscope. The damage characteristics of cracks with different structures were studied. Experimental results show that after HF etching, the cracks cross section turns into cosine pattern, and its laser induced damage threshold (LIDT) is not determined by the individual breadth or depth parameters, but by the breadth depth ratio of the crack cross section. The curve of LIDT versus the cracks breadth depth ratio was experimentally obtained. Finite difference time domain algorithm was used to calculate the electric field intensity distribution in the vicinity of a crack with cosine cross section, and the theoretical results agree well with the experimental ones.
2010, 59 (7): 5128-5134.
doi:10.7498/aps.59.5128
Abstract +
Density functional theory was performed to study the reaction mechanism of the reaction of FC(O)O2 with NO. The geometric configurations of reactants, intermediates, transition states and products were optimized by B3LYP method at 6-311G(d) level. The energies of stationary points along the pathway were also calculated. Intermediates and transition states were confirmed by the results of vibrational analysis. From the results of the mechanism of the reaction of FC(O)O2 with NO, we found that the reaction of FC(O)O2+NO has four pathways and several steps. Comparing the four pathways activation energies, we can find that the pathway FC(O)O2+NO→bM→bT→FC(O)O+NO2 is the main reaction pathway and the main products are FC(O)O radical and NO2, which is in good agreement with the result reported in the literature.
2010, 59 (7): 5135-5140.
doi:10.7498/aps.59.5135
Abstract +
The antisite defect, electronic conductivity and ionic dynamic properties of LiFePO4 have been investigated using first-principles density functional theory taking into account the on-site Coulomb interaction within the GGA+U scheme. Results indicate the Li/Fe exchange defect is the most preferred to occur in LiFePO4, which causes the Fe—O bond length to change in the direction favoring the formation of Li+ diffusion channels, hence improving the ionic dynamic properties of the olivine LiFePO4.
2010, 59 (7): 5141-5147.
doi:10.7498/aps.59.5141
Abstract +
In the present work, the processes of charge transport and electron transfer in dye-sensitized solar cell (DSC) under the stable illumination or forward bias were discussed, and the frequency response characteristic to the small perturbation of the light or voltage in DSC was also interpreted. The electron transit time and electron lifetime were investigated by electrochemical impedance spectroscopy (EIS), photoelectrochemical impedance spectroscopy (PEIS), intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS). The time constants determined by different measurement techniques were compared. The results showed that the process of charge transport and electron transfer has no significant influence on the time constants under low bias or low light intensity, and this process affected predominately the electron lifetime under high bias or high light intensity.
2010, 59 (7): 5148-5153.
doi:10.7498/aps.59.5148
Abstract +
The density distributions of water molecules and hydrogen bond in a specific nanocapsule at different temperatures were investigated by molecular dynamics simulation. We also analysed the intra-molecule angle and orientation of water molecules. The result indicates that, due to the confinement of carbon nanocapsule, water molecules are distributed mainly in three capsule-like layers, between which there are almost no water molecules. With temperature rising, the peaks of density distribution broaden to the nanotube wall. The hydrogen bonds are distributed similarly and affect the orientation of water molecules. There are a lot of hydrogen bonds at 1000 K, and the nanocapsule break with some molecules coming out at 3100 K.
2010, 59 (7): 5154-5162.
doi:10.7498/aps.59.5154
Abstract +
A newly developed Chernin cell was combined with the smog chamber for the volatile organic compounds(VOCs) detection using ultraviolet-visible spectroscopy. The principle, design and application of the Chernin cell were introduced in this paper. The Chernin cell has good vibrostability and is easily adjusted. The optical pathlength can be adjusted from 3 to 330 m. The system precision, stability and reliability were proved with NO2 detection. With 37 m absorption pathlength, the NO2 detection limit was 19.1 μg/m3. For the application of this system for VOCs detection, the concentrations of o, m, p-xylene and toluene in the smog chamber were measured with 36 m absorption pathlength, and the corresponding detection limits were 42.6, 15.1, 9.9 and 19.7 μg/m3 respectively.
2010, 59 (7): 5163-5168.
doi:10.7498/aps.59.5163
Abstract +
The coupling relation between heartbeat and respiration for the youth after exercise is investigated. We use empirical mode decomposition method as a filter to analyze the data of heartbeat and respiration obtained. It is shown that the cardiorespiratory phase synchronization still exists after exercise. Moreover, the ratio of phase-locking is different for different people and changes along with time. We proposed a measure of coupling relation based on transfer entropy, and found the coupling effect of respiration on heart is relatively large.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (7): 5169-5174.
doi:10.7498/aps.59.5169
Abstract +
We investigated the neutrino energy loss by electron capture of the nuclide 56Fe, 56Co, 56Ni, 56Mn and 56Cr in superstrong magnetic field at the crusts of neutron stars. The results showed that the superstrong magnetic field has only a slight effect on the neutrino energy loss rates when B13 G on surfaces of most neutron stars. Whereas for some magnetars, the range of the magnetic field is 1013—1015 G, the neutrino energy loss rates would be lowered greatly and may be even decreased more than five orders of magnitude by superstrong magnetic field.