Vol. 56, No. 2 (2007)
2007-01-20
GENERAL
2007, 56 (2): 597-603.
doi: 10.7498/aps.56.597
Abstract +
Combining the interpolation function, which has the delta function property and is constructed on the basis of radial basis functions and polynomial functions, using the local boundary integral equation method (LBIE), the local boundary integral equation method based on radial basis functions is presented for potential problem in this paper. The corresponding discrete equations are obtained. Comparing with the other meshless boundary integral equation methods, the present method has simpler numerical procedures, lower computation cost and higher accuracy. In addition, the essential boundary conditions can be implemented directly. Some numerical results to show the efficiency of the present method are given.
2007, 56 (2): 604-610.
doi: 10.7498/aps.56.604
Abstract +
The dynamic properties of one-dimensional cubic nonlinear Schr?dinger equation and drifting of the solution pattern are investigated numerically by using the symplectic method with different nonlinear parameters in the perturbation initial condition. The numerical simulation illustrates that the system shows different dynamic behaviors with varying nonlinear parameters, but the motion in the phase space is regularly recurrent. The results show that the drifting velocity for the small nonlinear parameter is small. With the nonlinear parameter increasing, drifting velocity of the solution pattern becomes faster at the same time of evolution.
2007, 56 (2): 611-619.
doi: 10.7498/aps.56.611
Abstract +
Applying the extended Riccati mapping approach to the (3+1)-dimensional nonlinear Burgers system, we obtain new variable separation solutions which contain an arbitrary function. With the help of numerical simulation of Mathematica, abundant special types of new localized excitations and fractals are discussed by selecting the arbitrary function appropriately. The solutions indicate that the extended Riccati mapping approach is valid for solving a class of (3+1)-dimensional nonlinear equations and can obtain much more abundant localized excitations than that of the (2+1)-dimensional nonlinear equations.
2007, 56 (2): 620-626.
doi: 10.7498/aps.56.620
Abstract +
By an improved mapping approach, a series of excitations of the (2+1)-dimensional Boiti-Leon-Pempinelli system (BLP) is derived. Based on the derived solitary wave excitation, we obtain some special chaotic solitons and the interaction between solitons.
2007, 56 (2): 627-636.
doi: 10.7498/aps.56.627
Abstract +
The paper gives a method for combining the auxiliary equation with hyperbolic function by function transition. And then the method is applied to construct the new solitary wave solutions and the trigonomical function wave solutions to the (2+1)-dimensional Hybrid-Lattice and discrete mKdV equation with the help of the symbolic computation system Mathematica.
2007, 56 (2): 637-642.
doi: 10.7498/aps.56.637
Abstract +
A sort of new method is put forward which is not similar to existing methods for a class of parabolic type systems with time-varying delays. By employing generalized Halanay's inequality, Dini derivative and the technique of differential inequality, a sufficient condition for the type of stabilization are derived. The stabilization criteria are delay-independent. A computation example is given to illustrate the proposed method. In addition, the distinct advantage of the method is that the criterions in the paper are easy to be checked, and can be applied in practice easily.
2007, 56 (2): 643-648.
doi: 10.7498/aps.56.643
Abstract +
The SiC nano-bar relaxation has been investigated using MD method. The Tersoff potential is adopted as the potential function. The characteristic of the homeostasis of SiC nano-bar relaxation is demonstrated. The nano-bar is affected by the strong surface effect and small size effect. The phenomena of torsion and bending is observed during the relaxation.
Hojman conserved quantities for systems with non-Chetaev nonholonomic constraints in the event space
2007, 56 (2): 649-654.
doi: 10.7498/aps.56.649
Abstract +
Hojman conserved quantities deduced by using the special Lie symmetry, the Noether symmetry and the Mei symmetry for systems with non-Chetaev nonholonomic constraints in the event space are studied. First, the differential equations of motion for the above systems are established. Second, the criterion of the Lie symmetry, the Noether symmetry, the Mei symmetry and the relation between them are obtained. Third, the conservation law obtained by Hojman is generalized and applied to the systems, and Hojman conserved quantities are obtained. An example is given to illustrate the application of the results.
2007, 56 (2): 655-660.
doi: 10.7498/aps.56.655
Abstract +
In this paper, the differential variational principles of mechanical systems in the event space are studied. The D'Alembert-Lagrange principle, the Jourdain principle, the Gauss principle and the universal D'Alembert principle in the event space are established on the basis of the D'Alembert principle of the system. The parametric forms of Euler-Lagrange, Nielsen and Appell for these principles are given, and the parametric form of Mangeron-Deleanu for the universal D'Alembert principle is deduced.
2007, 56 (2): 661-665.
doi: 10.7498/aps.56.661
Abstract +
The Mei symmetry of Tzénoff equations for nonholonomic systems under the infinitesimal transformation of groups is studied in this paper. The definition and the criterion equations of the symmetry are given. If the symmetry is a Lie symmetry, then the Hojman conserved quantity of the Tzénoff equation can be obtained by the Mei symmetry.
2007, 56 (2): 666-672.
doi: 10.7498/aps.56.666
Abstract +
For a Bose-condensed gas in an axially symmetric harmonic trap at zero temperature, a new trial wave function of the ground and single vortex states is considered based on the mean-field energy functional and variational method. Once the wave function is known, we can explore the particle-number dependence of relevant quantities, such as energy, chemical potential, aspect ratio of the velocity distribution and critical angular velocity for production of vortices. These results agree well with previous numerical solutions of the G-P equation given by Dalfovo et al.
2007, 56 (2): 673-677.
doi: 10.7498/aps.56.673
Abstract +
Based on the order rearrangement of single photon sequence, we present a multiparty controlled quantum secure direct communication protocol. The present protocol can be applied to some special scenario. In the protocol, the sender's secret message can only be recovered by the receiver under the permission of all the controllers. The security for the protocol is ensured by the quantum no-cloning theorem and the secret transmitting order of the single photon sequence. Moreover, all photons are used to encode the secret message except those chosen for eavesdropping check and it is unnecessary for the protocol to use entanglement. Our protocol is efficient and practicable.
2007, 56 (2): 678-682.
doi: 10.7498/aps.56.678
Abstract +
On the condition of electric-LO phonon strong coupling in parabolic quantum dot, we obtain the eigenenergy and the eigenfuctions of the ground state and the first excited state by using variational method of Peakar type. This system in quantum dot may be employed as a two-level quantum system-qubit. When the electron is in the superposition state of the ground state and the first excited state, we obtain the time evolution of the electron density. It is shown that the period of oscillation decreases with the strength of coupling increasing when the confined length is constant. And the period of oscillation increases with the confined length increasing when the strength coupling is constant.
2007, 56 (2): 683-685.
doi: 10.7498/aps.56.683
Abstract +
Taking for an example the Reissner-Norstrom black hole, we reinvestigate its Hawking radiation of charged particles via tunneling, which is viewed from the laws of black hole thermodynamics. After rewriting the imaginary part of the action into the related functions of laws of black hole thermodynamics, we find that there is an underlying relation between the first and second law of black hole thermodynamics and Hawking radiation via tunneling based on Parikh and Wilczek's original works. Moreover, if we consider the tunneling process as a reversible process, the result in Hawking radiation via tunneling is consistent with the first and second law of black hole thermodynamics. In other words, Parikh's conclusion is only valid for the reversible process.
2007, 56 (2): 686-692.
doi: 10.7498/aps.56.686
Abstract +
The tracking problem for a class of uncertain chaotic systems with dead-zone nonlinearity in the input function is considered in this paper. With the dead-zone nonlinearity in the controller, the disadvantage can be eliminated. The knowledge about the dead-zone nonlinearity in the input is unnecessary. To make this controller physically realizable, an extended state observer is used to estimate the unknown information. Numerical simulations are carried out to show the effectiveness of the design with respect to Duffing oscillator.
2007, 56 (2): 693-700.
doi: 10.7498/aps.56.693
Abstract +
Based on the fractal structure of strange attractor and self-affine property of time series, a method is proposed for predicting chaotic time series. The algorithm first exploits the iterative function system to track current chaotic trajectory and selects the segment which possesses the best self-affine property of the time series statistically. Then the prediction model is constructed according to attractor and coverage theorem. To illustrate the performance of the proposed model, simulations are performed on the chaotic Mackey-Glass time series, EEG signal and Lorenz chaotic system. The results show that the chaotic time series are accurately predicted, which demonstrates the effectiveness of the model.
2007, 56 (2): 701-706.
doi: 10.7498/aps.56.701
Abstract +
Separation of multiple mixing chaotic signals is an important issue in chaos and its applications. An instantaneous blind separation method for linearly mixed chaotic signals is proposed in this paper, in which the uncorrelation characteristics of chaotic signals are utilized. In the case of unknown mixture matrix and chaotic equations, the inverse matrix for reconstructing the source chaotic signals can be directly estimated from the observation by the approach of solving eigenvectors. The results by computer simulation indicate that the multiple mixing chaotic signals, by using the method, can be effectively separated from noisy background even when the signal to noise ration is low.
2007, 56 (2): 707-712.
doi: 10.7498/aps.56.707
Abstract +
A class of switchable four-dimensional chaotic systems is built by adding an additional state to the three-order Lorenz system or Liu system. Some of its basic dynamical properties are studied briefly, such as the feature of equilibrium, the chaos attractor, Lyapunov exponent and fractal dimension. An electronic circuit is designed to realize the class of switchable four-dimensional chaos systems. A method of chaos switch-synchronization between several chaotic systems based on nonlinear feedback control is proposed. Based on the stability theory, the functions of the nonlinear feedback control for synchronization of these systems are determined and the range of available feedback gain is derived.
2007, 56 (2): 713-719.
doi: 10.7498/aps.56.713
Abstract +
Two-phase learning method is considered in this paper to configure the RBF neural networks for chaotic time series prediction. When determining the hidden-layer centers with the unsupervised learning algorithm, a new distance measure is presented based on Gaussian basis, and the strategy of input-output clustering is employed in combination. The punishment factor in Gaussian basis distance is designed based on Fisher separable ratio, which can improve the clustering performance. Moreover, the introduction of input-output clustering strategy establishes the relation between the clustering performance and the prediction performance. Therefore, the RBF neural networks constructed by this method can not only assure the compact structure, but also improve the prediction performance. This method is applied to Mackey-Glass, Lorenz and Logistic chaotic time series prediction, and the results indicate its validity.
2007, 56 (2): 720-729.
doi: 10.7498/aps.56.720
Abstract +
To discuss the relation between complexity measures extracted from time series and flow pattern transition in gas-liquid two-phase flow, this paper analyzes the recognition capability of three complexity measures, including Lempel-Ziv complexity, spectral entropy and approximate entropy to different signals, such as periodic signal, stochastic signal, mixed stochastic signal and chaotic signal, and then the paper discusses the influence of the length of time series to the algorithms of the three complexity measures. Based on the above studies, we extracted the three complexity measures from eighty conductance fluctuating signals of gas-liquid two phase flow in vertical upward pipe. The results indicate that the three complexity measures are sensitive to the flow pattern transition in gas-liquid two-phase flow. By analyzing the rules of three complexity measures with the changes of gas-liquid two-phase flow parameters, we can get the dynamics structure inversion characters of gas-liquid two-phase flow, and they provide an efficient, supplementary diagnostic tool to reveal the flow pattern transition mechanism of gas-liquid two-phase flow.
2007, 56 (2): 730-739.
doi: 10.7498/aps.56.730
Abstract +
By analysis of local field distribution of the neurons in stationary state of associative memory neural networks, the role of the analog neuron transfer function in affecting the neural network performance is re-investigated. Different from the research done before, we find that the analog transfer function has no obvious advantages over the hard limit transfer function. Furthermore, analog transfer function sometimes produces a negative impact on certain functions of the network, such as the maximal storage capacity. We show that in pursuing the same performance a proper design rule is more essential than the choice of the transfer function.
The influence of the length and the velocy of vehicles on the mixed traffic flow in one-lane highway
2007, 56 (2): 740-746.
doi: 10.7498/aps.56.740
Abstract +
Based on NaSch traffic flow model, the mixed traffic flow model of whicles with different length and different maximum velocitdes on one-lane highway is proposed. Under periodic boundary condition, the influence of the length and the velocity of vehicles on the mixed traffic flow is studied by computer simulation.
2007, 56 (2): 747-754.
doi: 10.7498/aps.56.747
Abstract +
Analytical solution in terms of series for temperature oscillation in the heater/thermometer film is derived for 3ω measurements. The complex temperature solution is seperated into the real and imaginary parts. Analysis is performed to show the effect of the combined parameters of ac frequency, heater width and sample thermal properties on the temperature oscillation. The mathematical model for the measurement is corrected based on the solution. Accordingly, a 3ω setup is developed to determine thermal conductivity of 500 nm-thick thin film on Si substrate. Uncertainty analysis and comparison with the results of differential-3ω methods and published values are made, the results show good mutual agreement. The thermal conductivities of SiO2 film and Si substrate are determined simultaneously with the series solution and by extension to high frequency. The method is also employed to measure the thermal conductivity of the multi-layer antireflective coating of ZrO2/SiO2 deposited on Nd:YAG surface. The ZrO2 film has a thermal conductivity smaller than the volume value. The established 3ω setup and analytical method can be applied to investigate the thermal performance of thin film-substrate structures for use with micro-systems such MEMS.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2007, 56 (2): 755-763.
doi: 10.7498/aps.56.755
Abstract +
The action of type IIB superstring in AdS5S5 background given by Metsaev and Tseytlin(MT) can be reformulated in the Nambu-Goto form. For this form we give the new projection operator involving vielbeins in the target space to con-struct local κ-transformations which leave the action invariant. This new formulation of κ-symmetry(called target space form)is first suggested by Schwarz for the Green-Schwarz(GS) model. Due to the difference between GS model and MT model, our con-struction has some new aspects, which is applicable to all models similar to the MT model. An example is given for the AdS5S1 IIB superstring. We also study the κ-symmetry in target space form for the Polyakov model.
NUCLEAR PHYSICS
2007, 56 (2): 764-768.
doi: 10.7498/aps.56.764
Abstract +
Fusion barriers have been calculated for different orientations of the axial symmetry axis of deformed projectile-and target-nucleus. Using the concept of dinuclear system, considering the strong competition between fusion and quasifission processes, by solving the master equation numerically to calculate the fusion probability of superheavy nuclei, we have estimated the dependence of the fusion probabilities for 76Ge+208Pb and 48Ca+244Pu on the orientation angles of the symmetry axis of projectile-and target-nucleus, which shows that belly-belly is the most favorable orientation for synthesizing superheavy nuclei.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (2): 769-773.
doi: 10.7498/aps.56.769
Abstract +
In this paper，the structures and potential energy functions of the ground states of BeH, BeD, BeT molecules are investigated by quantum mechanical ab initio method in the level of QCISD(T)/aug-cc-pVTZ and CCSD(T)/6-311++G(3df，2pd). The spectroscopic data, ωe，ωeχe，Be，αe and De for the ground states obtained from the calculation are in good agreement with the data from experiment. It indicates that the potential energy functions of BeH, BeD, BeT can be expressed by the corrected Murrell-Sorbie functions.
2007, 56 (2): 774-780.
doi: 10.7498/aps.56.774
Abstract +
We solve the time-dependent Schr?dinger equation in two-color laser fields by using asymptotic boundary condition and symplectic algorithm. The P?schl-Teller potential model with three bound states was considered in the numerical calculation. The population of ionization, average distance, HHG and the population of transition were calculated. We show that the efficiency of high-order harmonic generation (HHG) in two-color laser field can be enhanced, and analyze the mechanism of the enhancement of HHG. We demonstrate qualitatively the enhancement of conversion efficiency of HHG by the transition probability.
2007, 56 (2): 781-785.
doi: 10.7498/aps.56.781
Abstract +
This paper reports the spectral characteristics of histidine and arginine in THz range by calculation and terahertz time-domain spectroscopy (THz-TDS). Absorption peaks are found at 0.88，1.64，2.23 THz (for histidine) and 0.99，1.47，2.60 THz (for arginine) by THz-TDS，respectively. The vibrational absorption spectra of the two molecules are calculated based on semi-empirical theory in the range of 0.1—10 THz. The calculated spectrum exhibits many absorption peaks and the first three of them are well comparable with the experiment results in the range of 0.2—2.8 THz. The vibration rotation modes corresponding to the absorption peaks of the molecules are presented. These results mutually validated both approaches, and can further be used in identification of molecules and experimental research in wider effective spectral range.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (2): 786-790.
doi: 10.7498/aps.56.786
Abstract +
A new method of multiresolution time domain analysis is proposed, which is based on compactly supported Daubechies scaling functions in the electromagnetic scattering of three dimensional objects. The highly linear dispersional properties are investigated. Using the interfaces of MRTD/FDTD technique, the connecting and absorption boundaries are dealt with. Numerical experiments show that, compared with conventional FDTD, this method can reduce cells without sacrificing solution accuracy, and uses less CPU time. Finally, the characteristics of PBG structure are obtained using this scheme.
2007, 56 (2): 791-797.
doi: 10.7498/aps.56.791
Abstract +
For the description of the focusing properties of a Bessel beam generated by an axicon, we first deduce a type of analytic expression other than Huygens-Fresnel diffraction integral theory. Based on the interferential theory, the analytic expression can be used to calculate the focusing beam evolution behind the focal plane of the positive lens and under the circumstance of the positive lens placed beyond the maximum non-diffraction distance, and can better illustrate the formation of the optical bottle beam. These results can not be described based on the Huygens-Fresnel diffraction integral theory. In addition, we get a different result from the one (that if z0max, hollow beam will be generated) obtained by Wei adopting geometrical optics. All of our theoretical calculations are confirmed by the experimental results.
2007, 56 (2): 798-804.
doi: 10.7498/aps.56.798
Abstract +
In this paper, the Goos-H?nchen shift on the interface of uniaxially anisotropic left-handed materials is investigated exhaustively, and the analytical expressions of Goos-H?nchen shift is presented for the cases of the optical axis being perpendicular and parallel to the interface, respectively. Moreover, the conditions for the existence and the sign of Goos-H?nchen shift are determined. Under Fresnel approximation, the expression of Goos-H?nchen shift around the critical angle is obtained, and the result shows that the shift around the critical angle is a function of the beam waist and incident angle. A simple approximate expression of the lateral shift with incident angle equals the critical angle is also presented. Thus, the general expression of Goos-H?nchen shift for any incident angles is obtained.
2007, 56 (2): 805-810.
doi: 10.7498/aps.56.805
Abstract +
Dispersion management is a technology that alternately and periodically uses fibers with opposite dispersion sign in wavelength-division multiplexing link, thus the path averaged dispersion coefficient over each period is close to zero. This paper studies the cross-phase modulational sideband instability in chain of periodic dispersion managed and lumped amplified fiber link. Analytisis and numerical simulation are applied to show that there are multi-sidebands in the dispersion managed fiber link if the path averaged dispersion exhibits the abnormal dispersion, while there is only the lowest order if the path averaged dispersion exhibits the normal dispersion. The results of analytical and numerical simulation methods are consistent.
2007, 56 (2): 811-818.
doi: 10.7498/aps.56.811
Abstract +
Using the vector Fourier transform and stationary phase method, an integral representation of the structure of image field in an aplanatic system with polarized point source located at arbitrary position on the optical axis is obtained. Effects of wide aperture angle in object space on the structure of image field are examined numerically for the case of linearly polarized illumination. Simulation calculations show that, in a plane perpendicular to the optical axis, if the object space aperture angle is wide, the distribution of magnetic field will not be identical to that of electric field after they are rotated 90° around the optical axis with respect to each other, the contours of distribution of the electric and magnetic energy densities and the Poynting vector are approximately elliptical, and the object space aperture angle is the dominant factor that makes the distribution of Poynting vector lose circular symmetry. At the same time, the major axis of the contour of distribution of the electric energy density is perpendicular to the direction of the electric vector in the object space when using small image aperture angle, and will turn graduately to the same direction as the electric vector in the object space with the increase of image aperture angle. These conclusions are completely different from the predications of the previous theory.
2007, 56 (2): 819-823.
doi: 10.7498/aps.56.819
Abstract +
When calculating the intensity propagating in the far field in coherent combining of fiber laser arrays, the previous approaches simply assumed that each aperture is a Gaussian amplitude distribution in a general way. The purpose of the present paper is to study the irradiance distribution where master-oscillators are partially coherent light, for example, the Gaussian-Schell model (GSM) beam. Based on the propagation law of partially coherent light, detailed numerical examples are given to illustrate the dependence of irradiance distribution on the coherence parameter of the GSM beam.
2007, 56 (2): 824-829.
doi: 10.7498/aps.56.824
Abstract +
On the basis of researchon the theory and mathe matics of interference data collection of the spatially modulated polarization interference imaging spectrometer designed by us, this paper mainly analyses and compares three different methods of spectrum reconstruction and interferogram processing. Specially, the authors introduce the nonparametric model of Music algorithm which is maturely used in power spectrum estimation into the spectrum reconstruction processing for the first time. This method prodigiously improves the resolution of reproduced spectrum, and provides a better math matic model for the improvement of resolving power in spectrum reproduction.
2007, 56 (2): 830-836.
doi: 10.7498/aps.56.830
Abstract +
We have investigated the coherence of resonance fluorescence for a coherently driven two two-level atoms coupled to a single-mode cavity in the bad cavity limit. By adjusting the detuning of the cavity-mode frequency from the driving filed frequency, we can enhance the fringe contrast factor as well as decrease the second order correlation function. The surprising effect produced by the detuning has an effect on the atomic dress-state population, which makes the fringe contrast factor and the second order correlation function changed evidently.
2007, 56 (2): 837-844.
doi: 10.7498/aps.56.837
Abstract +
The atomic dipole squeezing effect in the system of two identical two-level atoms in the Bell state interacting with the two-mode entangled coherent state field in Kerr medium are investigated by means of solving the Schrdinger equation and numerical calculations. The effects on the atomic dipole squeezing effect produced by the atomic initial state, mean photon number of light field, the degree of the entanglement of the entangled coherent field, the coupling strength of the Kerr medium with the light field and the coupling strength of dipole-dipole interaction between atoms are discussed. The results show that the dipole squeezing effect does not appear for the Bell state |β11>, while there can be dipole squeezing effect under certain conditions for the Bell states |β00> or |β01> or |β10>. In the latter case, the dipole squeezing effect depends on the coupling strength of the Kerr medium with the light field, the mean photon number and the degree of entanglement of the two-mode entangled coherent field.
2007, 56 (2): 845-853.
doi: 10.7498/aps.56.845
Abstract +
In this paper, the quantum statistical properties of a class of superposed q-deformed generalized coherent states |ψ>=a|β>+beiφ|βeiδ> are studied. The results show that the superposition of q-deformed coherent generalized states generally exhibits squeezing and anti-bunching effects. The change of the phase difference between two generalized coherent states, the phase difference between two superposition coefficients, and both the amplitude and phase of the inner product of two generalized coherent states play important roles in squeezing effect and anti-bunching effect.
2007, 56 (2): 854-858.
doi: 10.7498/aps.56.854
Abstract +
The orbital angular momentum (OAM) states can be used to construct a high-dimensional Hilbert space, which implies higher data density when applied in data storage. This work proposes a method to realize high density optical data storage by using OAM of light beam, with the encoded area illuminated by a light beam with certain OAM resulting in distribution of power in the OAM states (the spiral spectrum or OAM spectrum), and detection of the power distribution conducing to its decoding. A quadrant staircase structure (QSS) used as an encoded element can realize 57 different states, and it is expected to enhance the data density 6 times as high as the conventional method.
2007, 56 (2): 859-862.
doi: 10.7498/aps.56.859
Abstract +
By using slowly-varying envelope approximation, a family of solutions of the paraxial wave equation are found in theory, which represents a new family of ultrashort pulsed beams called ultrashort pulsed complex argument Sinc-Gaussian beams. These pulsed beams with a certain frequency have a nearly complex argument Gaussian profile, a sinc function temporal shape. The ultrashort pulsed complex argument Sinc-Gaussian beams and their propagation properties in free space are studied detailedly, such as intensity on the axis, transversal intensity distribution of the pulsed beams, polarity reversal, pulse time delay, etc..
2007, 56 (2): 863-870.
doi: 10.7498/aps.56.863
Abstract +
Some important parameters, such as gain, 3 dB bandwidth and threshold current of 1.3 μm quantum dot vertical-cavity surface-emitting laser (QD VCSEL) are theoretically investigated. Some methods are developed to improve the VCSEL's modulation response. Significant improvement are prediced for p-type modulation doping. In connection with the threshold characteristic, we found that a structure with short cavity, multilayer quantum dots stack, p-type modulation doping and double intracavity contact on an un-doped DBR is much better suited to high speed quantum dot VCSELs. The parasitic effects of the VCSEL are analyzed and the influence of packaging of the VCSEL on its modulation responds is analyzed.
2007, 56 (2): 871-877.
doi: 10.7498/aps.56.871
Abstract +
A new scheme for all-optical AND gate and NOR gate based on simultaneous four-wave mixing (FWM) and cross-gain modulation (XGM) in a semiconductor fiber ring laser (SFRL) is proposed, and a comprehensive broad-band dynamic model of this kind of all-optical logic gates is presented. By numerical simulation, the effects of the input signal peak power and the coupling of the couplers in SFRL on the output performances of the logic gates are analyzed.
2007, 56 (2): 878-882.
doi: 10.7498/aps.56.878
Abstract +
In this paper, the pulse waveform of stimulated Brillouin scattering (SBS) is investigated experimentally and theoretically. The variations of SBS pulse waveform with pump parameters, structural parameters and medium parameters are experimentally investigated with a Nd∶YAG Q-switched laser，and numerically simulated using SBS theory model. The theoretical calculations are in good agreement with the experimental results. The results indicate that modulation of pulse waveform is difficult to realige with low pump energy, short focal length, long lens-cell distance and long phonon life time. The influence of the pump parameters, structural parameters and medium parameters on SBS pulse waveform is discussed extensively.
2007, 56 (2): 883-888.
doi: 10.7498/aps.56.883
Abstract +
A novel dual-cell Brillouin oscillator-amplifier phase conjugate mirror for high energy and high peak power operation in double-pass solid state laser amplifier is described. Correction of static aberration and dynamic aberration induced in single-pass amplifier was achieved in the second passage through the aberrating medium under the condition of using the stimulated Brillouin scattering phase conjugate mirror as reflector. Output energy of 13 J was obtained with input energy of 7.1 J. An energy reflectivity of 65% and a conjugation fidelity of 90% were achieved by the use of this dual-cell phase conjugate mirror. Finally, the performance of this kind of SBS reflector in a double-pass amplifier has been compared to that of a flat mirror. The results show that the SBS reflector is highly effective in correcting the spatial aberrations of laser radiation. Excellent near-and far-field conjugation fidelities were obtained even with high input energy.
2007, 56 (2): 889-894.
doi: 10.7498/aps.56.889
Abstract +
It is shown from experiments that the stimulated Raman thresholds of the first and the second Stokes lines of CS2 are influenced by the absorption and fluorescence from the solution of β-Carotene in CS2 in liquid core optical fiber. The threshold of the first Stokes line of CS2 becomes higher when the concentration of the solution increases. And the second Stokes line of CS2 can be observed at a lower pump energy in the solution of β-Carotene in CS2 compared with that of the solution of pure CS2. Then the theoretic explanations are given and the theoretic results agree well with the experimental results.
2007, 56 (2): 895-901.
doi: 10.7498/aps.56.895
Abstract +
In the photoisomerized polymer，the perpendicular and all-optical control of optical spatial soliton is simulated by numerical method.The results show that if the controlling beam (c-beam) and the signal beam (s-beam) are coherent, the s-beam under controll of the c-beam will be dispersed, deflected or even collapse. The interactions depend on the difference of the two beam's initial phases，c-beam's intensity and the incident position of c-beam. The effect of perpendicular and all optical control has potential applieations in all-optical switching and optical integration.
2007, 56 (2): 902-907.
doi: 10.7498/aps.56.902
Abstract +
A model of integrated twin-guide semiconductor optical amplifier optical switch (ITG-SOA-Switch) is proposed. Comparison analyses with semiconductor optical amplifier (SOA) reveals that because of the combination of several physical effects by ITG-SOA-Switch, only a small increase of input power around 3 dB saturation point can cause a big decrease of gain. Theoretical analyes and the simulation results of 10Gbit/s wavelength conversion indicate that the extinction ratio of output converted signal of ITG-SOA-Switch can be greatly improved compared with that of input pump signal in a moderate pump power range.
2007, 56 (2): 908-915.
doi: 10.7498/aps.56.908
Abstract +
We investigate numerically the interactions of multiple partially incoherent spatial solitons in a nonlinear medium with logarithmic saturable nonlinearity based on the coherent density approach. Numerical results show that the interactions of incoherent solitons is somewhat similar to that of coherent solitons when the incoherence parameter is small; while for large incoherence parameter, the interactions of incoherent solitons are always attractive because the strong incoherent interactions blur out the initial relative phase between the incoherent solitons. Especially for the π-out-of-phase incoherent solitons, they can propagate in parallel under appropriate incoherence parameter. Mutual interactions of multiple partially incoherent spatial solitons can lead to a variety of induced waveguide configurations that allows steering, switching and guiding light with light.
2007, 56 (2): 916-921.
doi: 10.7498/aps.56.916
Abstract +
A method of manufacturing two-dimensional photonic crystals on several kinds of semiconductor materials in near infrared region by a focused ion beam is introduced, and the corresponding fabrication results are presented and show that the obtained parameters of fabricated photonic crystals are identical with the designed ones. Using the tunable laser source, the spectra of the fabricated passive photonic crystal and the active photonic crystal are measured. The experiment demonstrates that the focused ion-beam can be used to fabricate the perfect two-dimensional photonic crystals and their devices.
2007, 56 (2): 922-926.
doi: 10.7498/aps.56.922
Abstract +
A two-dimensional chessboard of non-Bravais lattice is designed in this paper: the square columns in photonic structure of a two-dimensional square lattice are rotated by 45°,and a cylinder is introduced into the center of each lattice unit cell. The complete photonic band gap in two-dimensional chessboard of non-Bravais lattice is calculated by the plane wave expansion method. The result shows that a gap width to midgap frequency ratio Δω/ω of chessboard non-Bravais lattice is almost 5 times that of the ordinary chessboard lattice, and the number of complete photonic band gaps is increased. Comparaed with other compound lattices, the optimal Δω/ω of chessboard non-Bravais lattice is 2.1 times that of a kind of compound lattices.
2007, 56 (2): 927-932.
doi: 10.7498/aps.56.927
Abstract +
Genetic Algorithms (GAs) were used to design triangular lattice photonic crystals with large absolute band-gap. Considering fabricating issues, the algorithms represented the unit cell with large pixels and took the largest absolute band-gap under the fifth band as the objective function. By integrating Fourier transform data storage mechanism, the algorithms ran efficiently and effectively and optimized a triangular lattice photonic crystal with scatters in the shape of ‘dielectric-air rod'. It had a large absolute band gap with relative width (ratio of gap width to midgap) 23.8%.
2007, 56 (2): 933-940.
doi: 10.7498/aps.56.933
Abstract +
Making use of the spectrum gain narrowing effect during the ultra-short pulse amplification in the gain media and the filter effect of the etalon, and adopting the principles of the regenerative amplifier, the multi-pulse coherent addition scheme is proposed and analyzed. In the small signal gain region of the ultra-short pulse amplification in the regenerative amplifier, theoretical analysis and numerical simulation have been made on the multi-pulse coherent addition stage. The simulation suggests that the width of the sub-pulse, the loss in the regenerative amplifier and the mismatch between the oscillator and the regenerative amplifier are the key factors affecting the temporal shape of the composite pulse, although they have little influence on its spectrum. Both the numbers of the constituent sub-pulses and the bandwidth of the etalon have influence on the shape and spectrum of the pulse.
2007, 56 (2): 941-945.
doi: 10.7498/aps.56.941
Abstract +
We designed a novel and low switching-power all-optical fiber switch. The highly nonlinear photonic crystal fiber and the bi-directional pumped Er-doped fiber amplifier are inserted into the Sagnac loop mirror simultaneously. The switching is realized based on cross-phase modulation because the symmetry of the loop is broken. The theoretical analysis shows that the switching-power is inverse proportional to the product of the amplifier gain and the nonlinear coefficient of the photonic crystal fiber. In our experiment, 40 mW switching-power and 15.9 dB switching-extinction are obtained; furthermore, the transmission of signal light is a cosine function of the peak power of the control pulse. All the results of experiment well agree with the theory.
2007, 56 (2): 946-951.
doi: 10.7498/aps.56.946
Abstract +
Confinement loss for the fundamental mode in the triangular lattice microstructured optical fibers with elliptical air holes is analyzed using the complex finite element method under the perfectly matched layer boundary condition. It is shown by the numerical results that the confinement losses decrease when the pitch of the air holes, the air-filling fraction and the rings of the air holes increase. In addition, the confinement losses are dependent on the fundamental mode polarization, and the confinement loss ratio of the y-polarized mode compared to the x-polarized mode increases with increasing pitch of the air holes, the air-filling fraction and the hole ellipticity. In the end, two kinds of highly nonlinear microstructured optical fibers that can achieve single-polarization, single mode transmission are designed.
2007, 56 (2): 952-957.
doi: 10.7498/aps.56.952
Abstract +
On the basis of optical resilient packet ring (O-RPR), this paper analyzes the control optical power needed for dual loop optical buffer (DLOB) to achieves ‘write-read’ successfully, and discusses the influencing factors on this power. Then we discuss the pulse compression and chirp caused by the signal pulse not being ideally square, and analyze the influence of power fluctuation and signal-to-noise ratio(SNR) of control light on output data.
2007, 56 (2): 958-967.
doi: 10.7498/aps.56.958
Abstract +
Erbium-doped hole-assisted lightguide fiber (EDHALF) is composed of a high-index core doped with erbium, a low index cladding and a small number of air holes surrounding the core. The finite element method is applied for solving the modal field of the EDHALF. The numerical calculation methods of the cutoff wavelength and mode field diameter are described in detail. The modified average population inversion iteration method is proposed for calculating the gain and noise figure of erbium-doped fiber amplifiers. The effects of the air holes on EDHALFs' cutoff wavelengths, mode field diameters and the gain coefficients of fiber amplifiers are studied. It's found that decreasing the relative hole-to-core spacing can make the cutoff wavelength move to shorter wavelength and decrease the mode field diameter. When the relative size of air holes is relatively large, further enlarging it only slightly changes the cutoff wavelength, mode field diameter and the maximum of the gain coefficient. Finally, four structural parameters, namely the EDHALF-core radius, the refractive index difference between the core and cladding, the relative hole-to-core spacing and the relative size of air holes are optimized in terms of the design criteria, which take into account the cutoff wavelengths of fundamental mode and the second order mode, the gain and noise figure of fiber amplifiers and the splice loss between the EDHALF and the conventional single-mode fiber.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2007, 56 (2): 968-976.
doi: 10.7498/aps.56.968
Abstract +
The influence of relativistic and thermal effects on plasma wave breaking has been studied by solving the coupled Vlasov-Poission equations. When the relativistic effect is not considered, the wave breaking will not occur, provided the initial perturbation is less than certain value as predicted previously, and the largest amplitude of the plasma wave will decrease with the increase of the initial temperature. When the relativistic effect is considered, wave breaking always occurs during the time evolution, irrespective of the initial perturbation amplitude. Yet the smaller the initial perturbation amplitude is, the longer is the time for wave breaking to occur. With large initial perturbations, wave breaking can always occur with and without the relativistic effect. However, the results are significantly different in the two cases. The thermal effects of electrons decrease the threshold value of initial amplitude for wave breaking and large phase velocity makes the nonlinear phenomenon occur more easily.
2007, 56 (2): 977-981.
doi: 10.7498/aps.56.977
Abstract +
Inductively coupled plasma (ICP) etching of InP in Cl2/BCl3 gas mixtures is studied in order to achieve low-damage and high-anisotropy etching of two-dimensional InP/InGaAsP photonic crystal. The etching mechanisms are discussed and the effect of plasma heating on wafer during etching is analyzed. It is shown that the balance between the undercut originating from plasma heating and the redeposition of sputtering on the side-wall is crucial for highly anisotropic etching, and the balance point moves toward lower bias when the ICP power is increased. High aspect-ratio etching at the DC bias of 203 V is obtained. Eventually, photonic crystal structure with nearly 90° side-wall is achieved at low DC bias after optimization of the gas mixture.
2007, 56 (2): 982-987.
doi: 10.7498/aps.56.982
Abstract +
For studing the transport of hot electrons in solid targets by transition radiation, the image pattern of spatial distribution and spectrum of optical emission were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer on the 100 TW femtosecond laser facility.The image pattern of spatial distribution has a disc-shape, in which is distributed a bright localized signal, which shows the filament effect during hot electron transport. The spectrum of optical emission has sharp peaks near the 3 and 3/2 multiple of the fundamental frequency, corresponding to the third-order harmonic and 3/2-order harmonics, respectively, which is ascribed to the coherent transition radiation (CTR) generated by microbunches of hot electron beams produced in transport. The intensity of transition radiation decreases with the increase of target thickness.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Phase constitution and solidification characteristics of undercooled Ag-Cu-Ge ternary eutectic alloy
2007, 56 (2): 988-993.
doi: 10.7498/aps.56.988
Abstract +
Liquid Ag38.5Cu33.4Ge28.1 ternary eutectic alloy was undercooled by a great degree up to 175 K(0.22 TE). X-ray diffraction analysis reveals that its rapidly solidified microstructure is composed of (Ag) solid solution phase, (Ge) semiconducting phase and η(Cu3Ge) intermetallic compound phase. With the increase of undercooling, there occurs a transition from the cooperative growth of three eutectic phases to the preferential nucleation and growth of (Ge) phase. The (Ag) and η phases usually grow to form pseudobinary lamellar eutectic structure. When the undercooling exceeds 80 K, the structural morphology of primary (Ge) phase transfers from faceted blocks to branched dendrites. Some (Ge) dendrites look like flowers, which usually have 5—8 lobes. In addition, the number of lobes tends to increase as undercooling increases. The crystal surfaces of the flower-like (Ge) dendrite are {111} planes and the dendrite grows along the 〈100〉 preferred growth direction.
2007, 56 (2): 994-998.
doi: 10.7498/aps.56.994
Abstract +
The matrix method is employed to analyze the optical activity of liquid crystal, and the matrix presentation of optical rotation is given. The magneto-optical rotation angle of BL-009 nematic liquid crystal is measured using JG-3 type continuous tunable magnetism device and infrared 1350 nm laser. The effect of magnetic field on optical rotation capability of liquid crystal is analyzed in detailed. The threshold of liquid crystal is discussed through experimental testing, and we reached at the conclusion that the rotation direction in liquid crystal is independent of the direction of magnetic field. The obtained result is useful for the design and manufacturing of liquid crystal device.
2007, 56 (2): 999-1003.
doi: 10.7498/aps.56.999
Abstract +
The microstructure change in the Vickers indent of the Zr65Al7.5Ni10Cu12.5Ag5 metallic glass at room temperature is investigated by transmission electron microscopy. It is found that the indentation-induced crystallization occurs namely underneath the indenter edges, where viscous flow is involved and crystals with the size larger than 1 μm appeav. The selected area electron diffraction shows that the crystalline phases are stable tetragonal CuZr2 or NiZr2, but not the icosahedral one that grows as metastable phase on heating. The local temperature rise during indentation can be ignored, which further suggests that the mechanically induced crystallization in a metallic glass is attributed to the viscous flow rather than the local heating effect.
2007, 56 (2): 1004-1008.
doi: 10.7498/aps.56.1004
Abstract +
Ni nanopowders with various grain sizes were successfully prepared by anodic arc discharging plasma method.The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected-area electron diffraction (SAED) to determine the crystal structure, lattice parameter, morphology and particle size. The experiment results indicate that the samples have fcc crystal structure as the bulk materials. The lattice parameter of Ni nanopowders is always larger than the equilibrium value of the perfect single crystal lattice, so the lattice expansion has taken place. The lattice parameter and the value of the unit cell volume increase significantly with the decrease of the grain size, and the increase in lattice parameter is inversely proportional to the grain size. The lattice expansion is the result of the interfacial energy and surface tension induced mutual attraction of Ni grains, and this phenomenon can be explained according to the thermodynamic theory.
2007, 56 (2): 1009-1013.
doi: 10.7498/aps.56.1009
Abstract +
In this paper, we have studied the formation of silicon nanoparticles on surfaces of carbon nanotubes by molecular dynamics simulation. We found that, due to the Si-nanotube interaction and the enormous curvatures of carbon nanotubes, Si atoms on the surface of a carbon nanotube prefer to form a three-dimensional nanoparticle rather than a thin film covering the nanotube.Small Si nanoparticles have similar atomic structures as are found in Si nanoparticles grown without any substrate.Large Si nanoparticles are elongated in the axial direction of the nanotube and have amorphous network structures of Si，different from the crystalline structure of Si nanoparticles without considering Si-nanotube interaction.
2007, 56 (2): 1014-1019.
doi: 10.7498/aps.56.1014
Abstract +
Large size (φ75 mm) high quality Nd∶YAG crystals were grown by the temperature gradient technique(TGT). The carbon atoms were eliminated after O2 annealing. We have studied the core distribution and growth stripes by Zygo interferometer and orthogonal polarization microscope. The absorption spectra of Nd∶YAG crystal at room temperature have been measured. The distribution of Nd ions in Nd∶YAG crystal were studied by using absorption spectra. A comparison of temperature gradient technique and Czochralski (Cz) grown Nd∶YAG crystals was made.
2007, 56 (2): 1020-1026.
doi: 10.7498/aps.56.1020
Abstract +
A composite was fabricated by an infiltration process using graphite particulates for damping enhancement phase and a Cu-11.9Al-2.5Mn (wt%) shape memory alloy as the matrix, and the internal friction of the resulting composite was studied. Two internal friction peaks were observed in the quenched specimens during heating at 240℃ and 370℃ respectively, of which only the evolvement and the mechanism of the low-temperature peak were investigated in the present study. It was found that, the peak only appears in the composite; the location of the peak is independent of frequency but its height increases with increasing frequency; the peak rises and shifts towards high temperature as the heating rate is increased; the height increases with increasing volume fraction of the graphite particulates; and it disappears after several thermal cycles. It is demonstrated from these features together with microstructure examinations that the peak results from the interaction between the applied stress and the dislocations in the matrix.
2007, 56 (2): 1027-1031.
doi: 10.7498/aps.56.1027
Abstract +
The cap layers of InAsP/InP SMQWs and InAsP/InGaAsP strained single quantum wells (SSQW) are etched to different depths using ICP. The PL intensity of the quantum wells is enhanced by different degrees after dry etching. The quantum well surface becomes rough and the microstructure inside the quantum well is changed during dry etching. The influence of surface roughness to the photoluminescence of quantum well is eliminated by selectively wet etching the InP cap layer of the SSQW. It is attained that after the cap layer is dry etched off about 20 nm the PL intensity of SSQW is enhanced about 1.8 and 1.2 times due to the change in microstructure and the roughening of surface, respectively.
2007, 56 (2): 1032-1035.
doi: 10.7498/aps.56.1032
Abstract +
The characteristics of oxidation of InN film in different oxygen atmosphere have been investigated. At the temperature under 400 ℃, the oxidation of InN film is difficult, but the oxidation of metal In is very easy. Thus, the oxidation of In is the main process during oxidation of the In-rich InN film under the temperature less than 400 ℃. As the annealing temperature is higher than 400 ℃, metal In and InN are oxidated meanwhile. Although oxidation under the temperature high than 400 ℃, InN is apparently oxidated very slowly. This may be due to the decomposition of InN. The oxidation rate under the ambience of wet oxygen is larger than that under dry oxygen.
2007, 56 (2): 1036-1040.
doi: 10.7498/aps.56.1036
Abstract +
Mg delta-doped GaN epilayers have been grown by metalorganic chemical vapor deposition, and their characteristics have been investigated. It is shown that not only the p-type conduction, but also the overall quality of p-GaN is improved by delta-doping. It is observed that the dislocation density is reduced due to the growth interruption. A pre-purge step has been employed during delta-doping process, but the carrier concentration was decreased by the pre-purge.
2007, 56 (2): 1041-1047.
doi: 10.7498/aps.56.1041
Abstract +
The gap breathers (GBs) in a one-dimensional Klein-Gordon diatomic chain are studied under rotating-wave approximation (RWA). The analytical investigation of heavy-particle centered symmetric mode (HS mode) has been implemented under the boundary condition of standing waves. We examine the effects of the coupling constant, nonlinear constant and the mass ratio on the GBs. The GB profiles are sensitive to the coupling constant, nonlinear constant and the mass ratio. As the coupling constant increases, the GB profiles become broader. But, with the nonlinearity and the mass ratio increasing, the GB profiles appear more localized.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2007, 56 (2): 1048-1053.
doi: 10.7498/aps.56.1048
Abstract +
In order to investigate the effect of N-doping on the electronic structure of anatase TiO2,and discover the mechanism of band gap narrowing after N-doping, we have carried out first-principles calculations based on density-functional theory(DFT) for anatase TiO2 system. Studies of band structures and densities of states and densities of electron distributing show that Ti atoms and N atoms at the conduction band(CB) area, happens a kind of strong correlated interaction, which will lead electrons of Ti atom on the 3d orbit to move to 2p orbit of N atom, and the entire conduction band will move to the Fermi level. Band gap will narrow and the Red Shift electrophoresis will happen. Theoretical result has been compared with the experiment result.
2007, 56 (2): 1054-1060.
doi: 10.7498/aps.56.1054
Abstract +
We demonstrate logic circuits with carbon nanotube field-effect transistors (CNTFETs). The p-type CNTFETs are fabricated based on single-walled carbon nanotubes and n-type CNTFETs are fabricated based on nitrogen-doped multiwalled carbon nanotubes. To be specitic, we demonstrate three types of logic circuits with CNTFETs, which include an inverter (a p-type CNTFET), a complementary inverter (a p-type CNTFET and an n-type CNTFET in a single clip), and a logic NOR (two p-type CNTFETs).
2007, 56 (2): 1061-1065.
doi: 10.7498/aps.56.1061
Abstract +
In this paper, a coupled 6×6 Hamiltonian valence eigenfunction is considered using effective mass approximation. Using a trial wave function separable in z direction and x-y plane, variational calculations are presented for energies of ground state and first excited state of heavy hole exciton and binding energies in ZnO film, and for radius of exciton under a variety of thickness d of ZnO film. And the correction of energies due to quantum tunnel effect of electronic wave function with the thickness d<2.0 nm is discussed.
2007, 56 (2): 1066-1074.
doi: 10.7498/aps.56.1066
Abstract +
A magnon-phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. The transverse acoustic phonon damping and longitudinal acoustic phonon damping are studied through Matsubara Green function theory, and transverse acoustic phonon damping and longitudinal acoustic phonon damping curves are calculated on the main symmetric point and line in the first Brillouin zone. It’s found that in the first Brillouin zone, on line Δ, there is no damping for the transverse acoustic phonon, on line Z, there is no damping for longitudinal acoustic phonon. In the first Brillouin zone, the transverse acoustic phonon damping is one order larger than the longitudinal acoustic phonon damping. The influences of transverse acoustic phonon damping and longitudinal acoustic phonon damping for different parameters on them are also illustrated in this article. According to the relationship between phonon damping and phonon lifetime, and the relationship between phonon damping and phonon density of state, the lifetime and density of state for transverse acoustic phonon and longitudinal acoustic phonon is discussed.
2007, 56 (2): 1075-1081.
doi: 10.7498/aps.56.1075
Abstract +
The experiment result shows that the holes generated by avalanche can be injected into gate oxide of a NMOSFET biased into snapback, and then both hole trapping and interface state generation can be found. These trapped holes may recombine with electrons tunneling into gate oxide due to the ultrathin gate oxide, and then many neutral electron traps would be generated and the gate oxide current would be increased. The threshold voltage would increase and the sub-threshold current would decrease when the injected electrons are trapped by the electron traps. The degradation of drain leakage current can be divided into two phases. Sub-threshold current is predominant in the first phase, while in the second phase gate current is predominant. After pre-HE stress, the generated interface states can reduce the number of holes being injected into gate oxide generated by avalanche process during snapback stress, which causes the MOSFET snapback degradation to decrease in on-state and off-state modes.
2007, 56 (2): 1082-1087.
doi: 10.7498/aps.56.1082
Abstract +
Wurtzite ZnO/MgO superlattices were successfully grown on Si(001) substrates at 750℃ using radio-frequency reactive magnetron sputtering method. X-ray reflection and diffraction, electronic probe and photoluminescence analysis were used to characterize the multiple quantum wells (MQWs). The results showed the periodic layer thickness of the MQWs to be 1.85 to 22.3 nm. The blueshift induced by quantum confinement was observed. Least square fitting method was used to deduce the zero phonon energy of the exciton from the room-temperature photoluminescence. It was found that the MgO barrier layers has a much larger offset than ZnMgO. The fluctuation of periodic layer thickness of the MQWs was suggested to be a possible reason causing the photoluminescence spectrum broadening.
2007, 56 (2): 1088-1092.
doi: 10.7498/aps.56.1088
Abstract +
Top-emitting organic light-emitting devies (TOLEDs) have been constructed with Ag/ITO reflective anode and LiF/Al/Ag semi-transparent cathode. The cavity effect have been researched by using Alq and TBADN:TBPe as emitting layers respectively. Different colors from the same emitting layer have been realized by changing the thickness of ITO. For Alq-based TEOLEDs, the full width at half maximum(FWHM) was narrowed to 20—40 nm from the 100 nm of bottom-emitting organic light-emitting devices (BEOLEDs). the EL peak was shifted from 500 nm to 584 nm by changing the thinckness of ITO. The maximun current efficiency of the TOLEDs is 1.77 cd/A, which approaches to the 1.8 cd/A of tranditional devices. For TBADN:TBPe-based devices, the FWHM was narrowed to 20 from BEOLEDs's 65 nm. the EL peak was shifted from 464nm to 532 nm by changing the thinckness of ITO, and navy blue with CIE coordinates x=0.141,y=0.049 have been obtained by TBADN:TBPe-based TEOLEDs with cavity effect.
2007, 56 (2): 1093-1098.
doi: 10.7498/aps.56.1093
Abstract +
We investigate the effects of H2O molecule environment on the transport properties of a seven-atom carbon wire coupled to two Al(100) electrodes based on a recently developed ab initio nonequilibrium Green function formalism. Our results show that the transport properties are sensitive to the variation of the number and the position of the H2O molecule on the carbon wire. Especially, the equilibrium conductance of the carbon wire with single H2O molecule exhibits an oscillatory behavior with the shift of positions of the H2O molecule. For the case of two H2O molecules, the contribution of the third eigenchannel becomes larger in some configurations. The calculated current-voltage curves show different behaviors with the variation of the positions of the H2O molecules. In certain cases, large negative differential resistance is found, but not in other cases.
2007, 56 (2): 1099-1104.
doi: 10.7498/aps.56.1099
Abstract +
Transport through the quantum wire with many side-coupled quantum chains is investigated by using a recursive Green's function technique. We obtained the modulation rules of the parameters N and NU, which are the number of side-coupled quantum chain and the quantum-dot number of side-coupled quantum chain, respectively. The results show that the recursive Green's function method not only can conveniently tune the model and the number of the quantum chain, but also can be applied to study the varied nanofabrication of quantum devices.
2007, 56 (2): 1105-1109.
doi: 10.7498/aps.56.1105
Abstract +
To visualize the relationship between the collector current and source-drain voltage in the SiGe/Si chare injection transistor (CHINT), the mathematical model of this device is set up by using the tunnel model of two-dimensional hole gas(2DHG)in SiGe/Si quantum well. Then the model is simulated by MATLAB, the result shows that the drain current shows strong negative differential resistance when VDS is about 1.5V, which is in accordance with the results of the other papers.
2007, 56 (2): 1110-1115.
doi: 10.7498/aps.56.1110
Abstract +
Surface roughening of Cu and Ta polycrystalline thin films deposited by magnetron sputtering at different homologous temperature Ts/Tm (Ts and Tm are the substrate temperature and the material melting point, respectively) have been studied using atomic force microscopy. With increasing Ts/Tm, the surface roughness of the films increased and growth exponent first increased and then decreased. The observed temperature dependence of growth exponent indicates a transition of growth modes from random growth at lower Ts/Tm through surface diffusion-dominated growth at intermediate Ts/Tm to anomalous scaling growth at higher Ts/Tm. We also found that the surface roughening of the films reflects the anomalous scaling behavior when the value of Ts/Tm is lower than 0.41, which implies that the boundary diffusion mechanism plays an important role in the scaling behavior of surface roughening.
2007, 56 (2): 1116-1120.
doi: 10.7498/aps.56.1116
Abstract +
The Co2+ ions doped ZnO diluted magnetic semiconductor films, Zn1-xCoxO, were prepared on glass substrate using PVA method. The structure of Zn1-xCoxO thin films with different x value and its photoluminescence properties were investigated. The vibrating sample magnetometer (VSM) measures the ferromagnetic properties of Zn0.88Co0.12O thin films at room temperature. We analyzed the influence of doping content on its luminescence performance, and discovered that with the doping content increasing, the blue luminescence peak shows a red shift.
2007, 56 (2): 1121-1126.
doi: 10.7498/aps.56.1121
Abstract +
Utilizing X-ray magnetic circular dichroism spectra we have investigated in-plane element-specific magnetic anisotropy in Co0.9Fe0.1 films. Apart from known field-induced easy axis during film growth, a soft axis perpendicular to it was observed, and the hard axis is 66°away from the easy axis. Thus in-plane bi-axisial anisotropy is realized. For different contents of Co and Fe, the variation trends of magnetic moment per hole in different magnetization directions are similar, and the values of magnetic moment of Fe is about 87% that of Co, which suggested that there exists strong ferromagnetic coupling between Fe and Co atoms.
2007, 56 (2): 1127-1134.
doi: 10.7498/aps.56.1127
Abstract +
La0.833K0.167MnO3 (LKMO) and La0.833K0.167MnO3/SrTiO3 (LKMO/STO) are fabricated at different temperatures. STLK08, STLK10 and STLK12 stand for the samples sintered at 800, 1000 and 1200℃ respectively. X-ray diffraction (XRD) shows that all of the three samples consisted of homogeneous solid solution phases. The resistivity for LKMO shows insulator-metal transition with decreasing temperature, but the resistivities of STLK10 and STLK12 show an insulator behavior over the whole temperature regime (4—300 K). The low-field (0.02 T) magnetoresistance increases from 0.2% to 11% with temperature decreases from 250 K to 4 K for STLK12 sample. The high field (μ0H=5.5 T) magnetoresistance almost increases linearly with decreasing temperature, which is much higher than the magnetoresistance of LKMO (The high field magnetoresistance are 65% and 40% at 4 K for STLK12 and LKMO, respectively). The enhancement in magnetoresistance is quantitatively explained by spin-polarized-tunneling at grain boundaries.
2007, 56 (2): 1135-1140.
doi: 10.7498/aps.56.1135
Abstract +
The nanocomposite Nd-Fe-B/FeCo mutilayer films have been prepared by rf sputtering. XRD results and HRTEM observation showed that as-deposited films deposited at substrate temperature of 300K were amorphous. The columnar grains of Nd2Fe14B phase with the c-axis perpendicular to the film plane developed after annealing at 923 K for 15 min. Nd2Fe14B grain size was about 10 nm in average and Nd-O particles of about 7 nm were dispersed within the grains and along the grain boundaries. The magnetization of these samples is found to increase with increasing FeCo layer thickness (tFeCo) and the coercivity decreases with increasing tFeCo. The multilayer films of maximum energy product is 200 kJ/m3 for tFeCo=5 nm at room temperature. The enhancement of the remanence and energy product in nanocomposite films is attributed to the exchange coupling between the magnetically hard and soft phases.
2007, 56 (2): 1141-1145.
doi: 10.7498/aps.56.1141
Abstract +
The magnetization measurements of Hg0.89Mn0.11Te sample grown by vertical Bridgman method have been carried out at 5 K under external field from -5200 to 5200 kA/m, and at 800 kA/m from 5 to 300 K with zero-field-cooling and field-cooling respectively using the superconducting quantum interference device (SQUID) magnetometer. Based on the mean field theory, a modified Brillouin function is well fitted with the data of magnetization vs magnetic field over the entire magnetic field range. The analysis indicates that there is an antiferromagnetic exchange coupling between Mn ions. The results of reciprocal susceptibility vs temperature show Curie-Weiss behaviors at temperatures above 40 K and a deviation from the Curie-Weiss law at temperatures from 5 to 40 K, which shows that the antiferromagnetic exchange coupling between Mn ions increases with decreasing temperature. The result was explained by extending higher-order terms in the calculation of susceptibility. Hg0.89Mn0.11Te is a paramagnetic material in temperature range from 5 to 300 K.
2007, 56 (2): 1146-1151.
doi: 10.7498/aps.56.1146
Abstract +
Based on effective medium approximation, self-consistent mean field approximation and the spectral representation method were adopted to investigate the temperature dependence of optical bistability of metal/dielectric granular composite. Numerical calculations were used to find out the temperature effects on optical bistability at different values of incidence frequency, volume fraction and shape factor. The results show that the emergence of optical bistability, optical bistability threshold and threshold width are all greatly dependent upon the temperature.
2007, 56 (2): 1152-1155.
doi: 10.7498/aps.56.1152
Abstract +
The High temperature Raman spectra of BGO crystal and melt were studied. The structures of BGO crystal and melt were analyzed. The rule of structure change of BGO crystal with increasing temperature was analyzed. The results show that the peaks of spectra move to the low wavelength and broaden in different degrees. The intensities of spectra peaks decrease, too. And there exit ［GeO4］ and ［BiO6］ bond structure in the melt of BGO crystal, while the bond between ［GeO4］ and ［BiO6］ bond structures disappear, so those two structures are unattached in the melt.
2007, 56 (2): 1156-1161.
doi: 10.7498/aps.56.1156
Abstract +
Multi-layer phosphorescent OLED with (tpbi)2Ir(acac) was fabricated which has the structure: ITO/CuPc (40 nm)/α-NPD (45 nm)/CBP: (tpbi)2Ir(acac) (3%, 30 nm)/BCP (20 nm)/Alq3 (20 nm)/LiF (1 nm)/Al (100 nm). Absorption spectra, phosphorescence lifetime of Ir complex, and I-V-L characteristic of the device was tested. The current of the device under low applied voltage conforms to the Richaardon-Schotty emission, and shows linear relationship under high voltage. Gauss peak fit shows the OLED spectra to be composed of α-NPD peak(450 nm), (tpbi)2Ir(acac) main peak(518 nm) and shoulder peak(543 nm). Maximum power efficiency of PHOLED is 12.1 lm/W (at 6V) with luminance 136 cd/m2, and the maximum luminance is 13500 cd/m2 with power efficiency 0.584 lm/W.
2007, 56 (2): 1162-1166.
doi: 10.7498/aps.56.1162
Abstract +
Nanocrystalline Gd2O3:Eu3+ was prepared by modified combustion synthesis using citric acid as the fuel and metal nitrates as oxidants. By using X-ray diffraction (XRD)，high resolution transmission electron microscopy (HRTEM) and fluorescence spectrophotometry, the structural, morphological and luminescent properties of the nanocrystals were investigated. The results showed that Gd2O3:Eu3+ nanocrystal with pure cubic phase was produced after the samples prepared using different citric acid-to-metal nitrate (C/M) molar ratios were calcined at 800℃ for 1 hour. The grain size was approximately 30 nm and the size distribution was narrow. The Gd2O3:Eu3+ nanocrystals whit C/M ratio 1.0 had the best crystallinity and strongest photoluminescence. The main emission peak of Gd2O3:Eu3+ nanocrystal was 612 nm, being attributed to 5D0→7F2 transition. The charge transfer state had an obvious red shift in the excitation spectrum. The efficient energy transfer from Gd3+ to Eu3+ was also observed. In addition, the influences of C/M molar ratio on crystallinity and luminescent properties were studied and discussed.
2007, 56 (2): 1167-1171.
doi: 10.7498/aps.56.1167
Abstract +
In this paper, we analyze and compare electrical compensation and deep level defects in semi-insulating (SI) materials prepared by Fe-doping and high temperature annealing of undoped InP. Influence of deep level defects in the SI-InP materials on the electrical compensation has been studied thermally stimulated current spectroscopy (TSC). Electrical property of the Fe-doped SI-InP is deteriorated due to involvement of a high concentration of deep level defects in the compensation. In contrast, the concentration of deep defects is very low in high temperature annealed undoped SI-InP in which Fe acceptors formed by diffusion act as the only compensation centre to pin the Fermi level, resulting in excellent electrical performance. A more comprehensive electrical compensation model of SI-InP has been given based on the research results.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2007, 56 (2): 1172-1176.
doi: 10.7498/aps.56.1172
Abstract +
Carbon-doping oxide materials (SiCOH films) with k of 2.62 are prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) from the mixture of decamethylcyclopentasioxane (D5) and oxygen (O2). This paper investigates the effect of O2-doping on bonding configuration, dielectric property and leakage current of the SiCOH low dielectric constant films. The results show that the leakage current can be reduced obviously on the premise that dielectric constant k is kept at a lower value by small O2-doping amount. For the SiCOH film deposited under O2 flow of 3 cm3/min, the dielectric constant k as low as 2.62 and leakage current of 8.2×10-9 A/cm2 can be obtained.
2007, 56 (2): 1177-1181.
doi: 10.7498/aps.56.1177
Abstract +
In this paper a series of hydrogenated silicon thin films were prepared by high-pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) using various plasma powers. The influence of plasma power on Raman crystallinity and deposition rate was investigated to study the silane depletion level during the deposition of silicon thin films. Based on these results the status of silane depletion were classified as un-depleted, depleted and over-depleted status. Additionally, the structural and opto-electrical properties were also investigated for those materials deposited under different silane depletion status. The results demonstrated that the μc-Si:H films, which are deposited at depleted status, have good opto-electrical properties and are suitable for application as intrinsic layers in solar cells.
2007, 56 (2): 1182-1187.
doi: 10.7498/aps.56.1182
Abstract +
Ag-doped BaTiO3 nanocomposite films have been synthesized on MgO substrates by excimer laser deposition. X-ray diffraction was used to characterize the structure and crystallinity of the films. The Ag chemical band and concentrations in the composite films were determined by X-ray photoelectron spectroscopy. The optical absorption were measured in the range of 300 to 800 nm and the absorption peaks due to the surface plasmon resonance of Ag particles were observed. z-scan results showed that the films exhibited large optical nonlinearities and the signs of the nonlinear absorption, β, and nonlinear refractive index, n2, changed with the increase of Ag concentration. The mechanism of the enhanced optical nonlinearities in Ag: BaTiO3 films is discussed.
Effect of high-intensity ultrasound on restraining solute segregation in Al-Si alloy casting process
2007, 56 (2): 1188-1194.
doi: 10.7498/aps.56.1188
Abstract +
The influence of high-intensity ultrasound on the microstructure and the distribution of solute elements Si in α (Al) of Φ10mm Al-1% Si alloy bonding wire produced by horizontal continuous casting have been investigated. Experimental results show that under high-intensity ultrasonication the microstructure is refined, the solid solubility and the uniformity of the distribution of Si in α (Al) are improved and the solute segregation is suppressed. The effect of high-intensity ultrasonic vibration on restraining solute segregation in Al-1% Si alloy ingot in horizontal continuous casting is explained from such factors as the diffusion of solute, solidification interval, solidifying front shape, temperature field, flow pattern and microstructure.
2007, 56 (2): 1195-1202.
doi: 10.7498/aps.56.1195
Abstract +
In this paper we briefly review the latest progress on the propagation of stress in granular bed and the resistant force of an object moving in granular media, and report our studies on the grain-size effect, which revals the discrete properties of granular media. We found that the sinking depth of a sphere on a granular bed driven by its own weight decreases monotonically with increasing grain-size. The supporting force of the granular bed experienced by the intruder sphere, during sinking, is measured. It is found that except for about 1 mm depth near the surface, the supporting force and the sinking depth of the sphere is related by a power-law with exponents between 1.5—1.0. The exponent decreases with increasing grain-size. This-size dependence of the power-law relation can be a macroscopic manifest of the reorganization of the stress chains in the granular system during the sinking process of the intruder sphere.
2007, 56 (2): 1203-1207.
doi: 10.7498/aps.56.1203
Abstract +
Based on equivalent particle scattering model, Mie theory is introduced to calculate the scattering phase function, anisotropy factor and scattering coefficient of biological tissue. Numerical results show that the anisotropy factor and scattering coefficients increase with the increasing of the equivalent particle's diameter when the tissue is irradiated by visible light; the anisotropy factor and scattering coefficients decrease monotonously with the increasing of incident light wavelengths when the equivalent particle's diameter is relatively small; the anisotropy factor and scattering coefficients have no monotonicity with respect to the wavelengths when the equivalent particle's diameter is big. The above numerical results explain the published experiments well.
2007, 56 (2): 1208-1213.
doi: 10.7498/aps.56.1208
Abstract +
The DNA molecule is considered as one-dimensional disordered binary system. Its electronic structure is discussed in terms of base pairs′ relative percentage and distribution using the density of electronic states which are calculated by the negative eigenvalue theory. The result shows that the effect of the base pairs′ relative percentage and distribution on the electronic energy state structure is great. In other words, the sequence of the base pairs plays an important role in determining the electronic structure.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (2): 1214-1223.
doi: 10.7498/aps.56.1214
Abstract +
According to synchrotron radiation theory, we derive the absorption coefcient, emission coefficient, and the emission intensity from relativistic electrons in the plasma under the different kinds of magnetic fields. Furthermore, we study the maser effect of the synchrotron radiation. The effects of two kinds of magnetic fields are investigated, the first kind is a curved magnetic field, but its strength is homogenous. The other is a dipole magnetic field. We find some special characteristics in the dipole magnetic field. Because of the uncertainty of the energy distribution spectrum of electrons, we choose three typical energy distribution spectra, namely the power law spectrum, Gauss spectrum and thermal spectrum. By calculating the emission intensity, we find the maser effect of synchron-curvature radiation under several kinds of astronomical condition. It is clearly shown that the maser emission of the synchrotron radiation does exist in plasma environment. These results could give some explanations for the atmospheric radiation of planets and might be helpful to solve the problems of the high brightness temperature of some radio sources.
2007, 56 (2): 1224-1230.
doi: 10.7498/aps.56.1224
Abstract +
The activity of the sunspot influences the space environment directly. In order to guarantee the flight safety of the spacecraft in the space, it is necessary to predict the sunspot number effectively. To solve this problem, a time series prediction model based on the process neural network with time-varying threshold functions is proposed. To simplify the calculation, a learning algorithm based on the expansion of the orthogonal basis functions is developed. The functional approximation capability of the proposed prediction model is analyzed, and the effectiveness of the prediction model and its learning algorithm is validated by the prediction of the Mackey-Glass time series. Finally, the proposed time series prediction model is utilized to predict the smoothed monthly mean sunspot numbers in solar cycle 23, and the results are satisfying. The application results also indicate that in comparison to other traditional prediction methods, the prediction method used in this paper has a higher prediction accuracy, thus it has theoretical meaning and practical value for the space environment prediction.
