Vol. 55, No. 7 (2006)
2006-04-05
GENERAL
2006, 55 (7): 3203-3207.
doi: 10.7498/aps.55.3203
Abstract +
Information barrier technology has become more and more important in the R&D of radiation fingerprint verification associated with classified items such as nuclear warheads, nuclear components and military-used nuclear materials. The function of information barriers is two-fold: one is to prevent the classified information from leaking out; the other is to provide creditable verification. To fulfill these two functions, the information barriers for a viable verification system (including all its hardware and software) must be designed on the basic principles of protecting classified information and the ability to authenticate. The Spectral Blanking-out Controller (SBC) is developed to illustrate the two functions of the information barriers and to explore some practice measures to meet the required design fundamentals. This paper briefs the task assigned to the SBC, the specific design concerns and the practical information barrier measures. The R&D of the SBC embodies the concepts of information barrier technology and has to confom to the basic guidelines: If a verification system is expected to possess strict information barriers, the design of the system must be integrative with due considerations given to the factors such as the efficiency of the verification technique, the possible measures to protect the classified information from directly or indirectly leaking out, the complete openness in all aspects of the system for the inspectors to authenticate the system for the sake of achieving certain degree of confidence on the verification results.
2006, 55 (7): 3208-3214.
doi: 10.7498/aps.55.3208
Abstract +
The uncooled IR thermal imaging technology with its wide applications in military, medical and industrial areas has been an active topic in international research. Thermal imaging based on optical readout bi-material microcantilever array is a new concept in methodology. In this paper, a new kind of bi-material micro-cantilever unit with multi-fold legs and interval gild structure is designed and its thermal and thermo-mechanical performance are analylized. A 100×100 microcantilever array is fabricated as a FPA (focal plane array), and by using this FPA, a thermal image of a room-temperature body (human body) is successfully detected. The NETD (noise-equivalent temperature difference) is about 200mK.The experimental results are well accordant with the thermal analysis of the microcantilever unit.
2006, 55 (7): 3215-3222.
doi: 10.7498/aps.55.3215
Abstract +
By combining the reproducing kernel particle method (RKPM) and boundary integral equation method for elasticity, the reproducing kernel particle boundary element-free (RKP-BEF) method is presented in this paper. Formulae for the RKP-BEF method are derived. The discrete boundary integral equations of the RKP-BEF method are established by considering the numerical integral schemes and the treatment of singular integrals, and the formulae of the displacement and stress of inner points for the RKP-BEF method are given. The RKP-BEF method has a higher precision as the smoothness of the shape function of RKP method is the same as that of the kernel function, and the values of polynomials at interpolating points can be exactly reconstructed. Numerical examples are given for verifying the effectiveness and correctness of the RKP-BEF method presented in this paper.
2006, 55 (7): 3223-3228.
doi: 10.7498/aps.55.3223
Abstract +
An effective fuzzy edge detection algorithm is proposed in this paper. This novel algorithm is different from other fuzzy edge detection algorithms based purely on image enhancement technology. Several kinds of information are used as the characteristics of edge detection, and fuzzy logic is used to fuse the information together. So, the edge detecting process is more effective and gives much better edge information. It is proved that this algorithm is applicable to detect the edge of highly-noisy images.
2006, 55 (7): 3229-3232.
doi: 10.7498/aps.55.3229
Abstract +
A time delay sea-air oscillator model is studied. Using the perturbation theory and corresponding method, the asymptotic expansion of the solution for the sea-air oscillator model is obtained.
2006, 55 (7): 3233-3236.
doi: 10.7498/aps.55.3233
Abstract +
A nonlinear transmission system for the laser pulse amplifier is discussed. Using the generalized functional-variational iteration theory and method, the corresponding approximate solution of the system is obtained, which facilitates the design of laser pulse amplifiers.
2006, 55 (7): 3237-3240.
doi: 10.7498/aps.55.3237
Abstract +
The perturbation of symmetries and adiabatic invariants for Lagrangian system are studied. The exact invariants introduced by the Lie symmetries of Lagrangian system without perturbation are given. Based on the definition of high-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for Lagrangian system with the action of small disturbance is investigated, and a type of Hojman adiabatic invariants of the system are obtained. An example is given to illustrate the application of the results.
2006, 55 (7): 3241-3245.
doi: 10.7498/aps.55.3241
Abstract +
The conservation theorems of the Lagrange's equations for generalized nonconservative systems in terms of quasi-coordinates are studied by using the method of integrating factors. The differential equations of motion of systems are written. The definition of integrating factors is given. The necessary conditions for the existence of the conserved quantity are studied in detail. Finally, the conservation theorem and its inverse are established, and an example is given to illustrate the application of the result.
2006, 55 (7): 3246-3254.
doi: 10.7498/aps.55.3246
Abstract +
On the basis of homogeneous balance method, tanh-function method and auxiliary equation method, new types of exact solitary wave solutions of the dispersive long-wave equation and Benjamin equation are constructed by using a new auxiliary equation and with the aid of computer algebraic system Mathematica in this paper. This method also can be used to find new solitary wave solutions of other nonlinear evolution equations.
2006, 55 (7): 3255-3258.
doi: 10.7498/aps.55.3255
Abstract +
A single N-dimensional quNit quantum secret sharing scheme is proposed. In this scheme, extending two bases and four states used in Bennett and Brassard protocol(BB84) to multi-bases and multi-states,a distributor sends the encoded N-dimensional quantum system to one of his two recipients. After receiving the quNit, the recipient makes a unitary operation on it using a N-dimensional cloning machine, and then sends it to the other recipient. After being informed that the second recipient has received the quNit, the distributor announces his preparing base, and then the two recipients perform measurements on their systems using the same base as the distributor and obtain the sent quantum state after collaboration. The security of the scheme is based on quantum non-cloning principle. In addition, this scheme has the features of great information flux and high efficiency. At last, the generalization from two recipients to N recipients is discussed.
2006, 55 (7): 3259-3264.
doi: 10.7498/aps.55.3259
Abstract +
Closely related to the quantum information processing in solid states, we study the quantum measurement of single electron state by a mesoscopic charge-sensitive detector, namely the quantum point contact (QPC). We find that the conventional Lindblad-type master equation is not appropriate for describing the underlying measurement dynamics. The treatment developed in this work properly accounts for the energy-exchange between the detector and the measured system, and its role on the detailed-balance relation. A valid description for the QPC measurement dynamics is provided which may have impact on the study of quantum measurement and quantum feedback control in solid states.
2006, 55 (7): 3265-3271.
doi: 10.7498/aps.55.3265
Abstract +
Based on the Gross-Pitaevskii(G-P) energy functional and variational method, we present a new method to find the ground state wave function for Bose-condensed gas in a harmonic trap at zero temperature. With this method we are able to find the analytic expression of ground state wave function and explore the relevant quantities, such as energy, chemical potential and so on. These results agree well with previous ground state numerical solutions of the G-P equation given by Dalfovo et al. Under the large number of particles N limit for repulsive interaction, our results and Thomas-Fermi approximation model approach to reaching unanimity. This new method is simple compared to other methods used to solve numerically the G-P equation, and one can obtained the analytic and reliable results.
2006, 55 (7): 3272-3276.
doi: 10.7498/aps.55.3272
Abstract +
Using the improved brick-wall film model， we calculated the entropy of Dirac field in a generalized non-stationary spherically symmetric black hole with charge. From the point of view of the model， these entropies are nothing but the entropy of the black hole. The result showed that this entropy is proportion to the area of event horizon.
2006, 55 (7): 3277-3282.
doi: 10.7498/aps.55.3277
Abstract +
Modulated stochastic resonance method which can detect weak periodic signals under strong noise in wide parameter conditions is proposed in this paper. The high frequency weak signal mixed with noise is modulated to a low frequency difference signal. The signal conforms to the adiabatic elimination theory. So when it acts on stochastic resonance system, the stochastic resonance can arise. If the low frequency signal is demodulated, the original high frequency weak signal mixed with noise can be relrieved. To deal with the unknown frequency mixed with noise, the frequency of modulate oscillator is changed continuously to achieve a suitable difference frequency signal for inputting to stochastic resonance system. According to the change of resonance spectral peak value, the unknown frequency can be found from the demodulated signal. The method is effective for future application.
2006, 55 (7): 3283-3288.
doi: 10.7498/aps.55.3283
Abstract +
In this paper, a scheme for digital secure communications is proposed by using different drive functions of hyperchaotic systems based on APD approach. Two different drive functions can be alternately sent according to the transmission of binary signal “0" and “1", which will enhance the complexity and decrease the correlation of transmitted signals. Meanwhile, by designing compound nonlinear function transformation for transmitted signals to further intercalate the secret key, a determined intruder is very difficult to retrieve the contents of message signal using forecasting method. Theoretical analysis and numerical simulation results show that this method is effective.
2006, 55 (7): 3289-3294.
doi: 10.7498/aps.55.3289
Abstract +
A new type of four-dimensional chaotic system is studied by constructing a new nonlinear function. The characteristic of this chaotic systems is that the 2n+2 scroll chaotic attractors are found in our computer simulation with the natural number n increasing, and the bounds of the chaotic attractors is modified by changing the control parameter k. Finally, the circuit is designed and emulated on EWB platform.
2006, 55 (7): 3295-3301.
doi: 10.7498/aps.55.3295
Abstract +
In order to generate complex chaotic attractors, we construct a new three-dimensional quadratic autonomous chaotic system, in which each equation contains a single quadratic cross-product term and a system parameter. Basic dynamic properties of the new system are investigated via theoretical analysis and numerical simulation using the Lyapunov exponent spectrum and bifurcation diagram. Our results show that this system has five equilibria, therefore is not topologically equivalent to the Lorenz, Rsslor or the Chen and Lü systems, and the new system is chaotic when its parameters satisfy certain conditions. Compared with the systems mentioned above, the proposed system has larger positive Lyapunov exponent，displays a complex attractor and some other interesting properties. An electronic circuit was designed to realize the new chaotic system. Experimental chaotic behaviors of the system were found to be identical to the dynamic properties predicted by theoretical analysis and numerical simulations.
2006, 55 (7): 3302-3306.
doi: 10.7498/aps.55.3302
Abstract +
The paper introduces a new method for fuzzy modeling based on a hierarchical fuzzy-clustering scheme. The method consists of a sequence of steps aiming at developing a Takagi-Sugeno (TS) fuzzy model of optimal structure. The premise parameters' identification consists of two steps: Start from an initial fuzzy partition of input space by a nearest-neighbor clustering method to get the number of rules and the initial clustering center; then premise parameters are further processed using a fuzzy C-means algorithm (FCM). The conclusion parameters are identified by the weighted least square method and further optimized by selective recursive least square method. To illustrate the performance of the proposed method, simulations on chaotic Mackey-Glass time series prediction are performed. The results show that the chaotic Mackey-Glass time series are accurately predicted, which demonstrates the effectiveness of this method.
EDITOR'S SUGGESTION
2006, 55 (7): 3307-3314.
doi: 10.7498/aps.55.3307
Abstract +
This paper further analyzes some basic properties of a new complex four-dimensional continuous autonomous chaotic system, in which each equation contains a cubic cross-product term. The new system has 9 equilibria which display graceful symmetry with respect to the origin and coordinate planes, and they are similar with respect to their linearized characteristics and invariant manifolds. Two coexisting symmetric double-wing chaotic attractors are described. Finally, an analog circuit is designed to implement the new system, which shows a good agreement between numerical simulation and experimental results, and explains their significant distinction in applications due to difference in frequencies.
2006, 55 (7): 3315-3321.
doi: 10.7498/aps.55.3315
Abstract +
Taking into consideration the Coulomb interaction between two ions trapped in the coplanar Paul trap,the exact solutions of the Schrdinger equations of the two-ions system are obtained.The energy level degeneracy for center-of mass is obtained using the exact solutions. We also calculate the equilibrium distance of the ions and several state functions of the low energy levels. The radial probability distribution graph for the center of mass is plotted using a computer program.
2006, 55 (7): 3322-3327.
doi: 10.7498/aps.55.3322
Abstract +
This paper proposes a method of non-autonomous feedback control, and proves its validity by the stability theory. This method is used in numerical emulation of energy resource chaotic system and Arneodo system. The result indicates that it is correct and feasible.
2006, 55 (7): 3328-3335.
doi: 10.7498/aps.55.3328
Abstract +
A cellular automaton model for the bottleneck in high speed traffic caused by a bridge is proposed. It takes the initial density apart into six regions. Based on the mean field theory and the results of definitive NS model, the relations of car density of every line are given. The simulation results show that the theoretical model is correct.
2006, 55 (7): 3336-3342.
doi: 10.7498/aps.55.3336
Abstract +
In this paper, the correlation functions in the CA (cellular automaton) traffic models incorporating the `slow-to-start' rule, such as VDR model, BJH model and T2 model, are systematically studied at different traffic densities. The results show that there are anti-correlations and correlations between cars at low density. When anti-correlation disappears with the increases of density, it means the transition from free flow to jamming. In order to study the characteristics of phase transition, we study the order parameters of these models with the delay probability and slow-to-start probability. We found that the CA traffic model with ‘slow-to-start’ rule will change the characteristics of phase transition. Independently of the delay probability and in the case of less than maximal velocity, the transition from free flow to jamming in the CA model with slow-to-start probability not exceeding 0.5 is the second phase transition, which has an analogy to one in the deterministic NaSch model. Otherwise, the first phase transition will appear. Under conditions of stochastic delay, the crossover phenomena will occur. When the limiting velocity has larger values, it will show the first phase transition in spite of the delay probability.
2006, 55 (7): 3343-3348.
doi: 10.7498/aps.55.3343
Abstract +
With ［Si］ time series of No. 1 BF at Laiwu Iron and Steel Group Co. and No.6 BF at Linfen Iron and Steel Group Co. as sample space, and based on rescaled range analysis and method of box dimension, the Hurst exponents of ［Si］ time series of these two BFs and the box dimensions are figured out to be ranging from 0.257 and 0.224 and 1.712 and 1.724, respectively. The complex degree of ［Si］ time series is described, and it is also proved that ［Si］ time series is a long-term negative association fractal time series. With the correlative parameter fixed, the simulated trend was pictured by the theory of iterated function system.
2006, 55 (7): 3349-3354.
doi: 10.7498/aps.55.3349
Abstract +
According to the experimental observation of Au atomic aggregations on a molten glass surface, we established a computational model to simulate Improved Restricted Cluster-Cluster Aggregation (IRCCA) on nonlattice substrates with regularly and randomly distributed impurities. In the model, the random diffusion step and rigidity rotation around the mass center of cluster were considered. The aggregation process was simulated and the influence of the distribution of impurity on the properties of aggregations was systemically investigated. The results show that regularly distributed impurities play a more important role in restricting the aggregation of clusters than randomly distributed impurities, resulting in a higher number density of fractal aggregates with smaller radius of gyration and fractal dimension.
2006, 55 (7): 3355-3359.
doi: 10.7498/aps.55.3355
Abstract +
Proposed an one-dimensional sandpile model which include avalanche probability, and performed computer simulation by cellular automata method. The results show that there are two critical points p1 and p2 when avalanche probability p transits from 0 to 1. The self-organized criticality(SOC) behavior can be found in the model when p12. There is a sharp transition between the trivial behaviour and the SOC behaviour in the model. When there is SOC, the SOC behaviour is universal, the two critical exponents are 1.50±0.02 and 1.58±0.15. With the model, the SOC phenomenon appearing in the experiment of one-demensional rice-pile is well explained.
2006, 55 (7): 3360-3362.
doi: 10.7498/aps.55.3360
Abstract +
Base on the establishment of an ambipolar transport equation of conductivity modulation base with non-uniform lifetime, WKB solutions of excess carrier profiles under different boundary conditions have been obtained by using Liouville-Green transform. The results can be used in modeling of conductivity modulation power devices under localized lifetime control.
2006, 55 (7): 3363-3367.
doi: 10.7498/aps.55.3363
Abstract +
A new confocal measurement method based on superresolution image restoration and shaped annular beam is proposed. Firstly, we employ a binary optical element (BOE) to shape a Gaussian beam into an annular beam which preliminarily improves the lateral resolution of a confocal microscopy system, then we use a superresolution image restoration technique based on the theory of maximum likelihood estimate (MLE) to retrieve the lost high frequency information of the testing image, which further enhances the lateral resolution. The experimental results indicate that a lateral resolution of better than 0.1μm is achieved when λ= 632.8nm and N.A.= 0.85. In addition to the distinct superresolution effect, the proposed method also has the advantage of low cost, therefore, it provides a novel technical way to improve the lateral resolution of a confocal microscopy system.
2006, 55 (7): 3368-3374.
doi: 10.7498/aps.55.3368
Abstract +
This article has introduces the basic components and characteristics of a femoto-second electron diffraction system, i.e. the photo-cathode, magnetic lens, deflector and detector with doubled MCP etc., and demonstrated our design method and results. The photo-cathode is an Ag film deposition on a sapphire disk and the femtosecond electron pulses are accelerated to 50 keV through an extraction electric field of 10kV/mm between the photocathode and the extraction mesh. After extraction, the electron pulses are reshaped in size by a 100 μm pinhole, which screens out electrons with larger elevation angle and makes the passed electrons flying almost parallel to the axis, which results in a reduced electron beam spot. The beam is collimated with a magnetic lens and positioned to the sample by a pair of deflection plates for diffraction measurements. The electron diffraction images are recorded with a two-dimensional imaging system composed of a Chevron-type microchannel plate and a P20 phosphor screen on an optical-fiber faceplate. The initial position, kinetic energy and angle distribution of the photoelectrons is sampled with Monte Carlo method. The electric field is calculated with finite difference formula, and the magnetic flux of the focus region is calculated with finite elements methods, and the electron trajectory is traced with Runge-Kutta method. We analysized the temporal and spatial distribution of 3000 electrons when they reached the prime plane and give out the temporal and spatial modulation transfer function of the femoto-diffraction system.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2006, 55 (7): 3375-3379.
doi: 10.7498/aps.55.3375
Abstract +
In this paper, the D→Klv～l decay is researched using by QCD light cone sum rules. Firstly, the form factor of D→K is calculated by choosing a new correlative function to eliminate the effect caused by the uncertainty of twist-3 function, so the calculation result of form factor is more precise, and the branching ratio is consistent with the experimental data.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (7): 3380-3385.
doi: 10.7498/aps.55.3380
Abstract +
The energy spectrum and oscillator strength of hydrogen atom in static magnetic field have been calculated using basis set method. Both the radial and angular wave-functions are expanded in terms of B-spline functions. The resultant size of Hamiltonian matrix is reduced considerably, which enables the calculations to be carried out in personal computer. Diamagnetic spectrum of Rydberg hydrogen atom from -40cm-1 to the field free ionization threshold was obtained with high accuracy. The results have been compared with those of most accurate ones in the literature. The method presented in this paper can be extended easily to the region with positive energy and to the cases of non-hydrogen atoms and the crossed field problem.
2006, 55 (7): 3386-3392.
doi: 10.7498/aps.55.3386
Abstract +
A laser phase determination method and a transfer equation which makes use of the proportional term of the measured photoelectron energy spectrum are presented to directly measure the detailed temporal structure of a narrow bandwidth attosecond XUV pulse. The method is based on the spectrum measurement of electrons generated by XUV photo-ionization interacting with a femtosecond laser field. The results of the study suggest that the measurement should be taken at 0° or 180° with respect to the linear laser polarization. The method has a temporal measurement range of about half a laser oscillation period. The temporal resolution also depends on the jitter and control precision of the laser and XUV pulses.
2006, 55 (7): 3393-3395.
doi: 10.7498/aps.55.3393
Abstract +
It has great meaning to study the effect of a moving mirror in a cavity on the dynamic behavior of a two-level atom injected in the cavity. In this paper, for a system composed of a two-level injected atom and a single-mode field and a moving mirror in the cavity (the moving mirror to be regarded as a quantum harmonic oscillator with frequency ωm), the time-evolution of its state is obtained by means of complete quantum theory in the interaction picture. The time-evolution of the atomic population is derived on the basis of former investigations. It is found that the atomic population oscillates near its initial value. The result shows that the periodic motion of the mirror has a periodic effect on the atomic population.
2006, 55 (7): 3396-3402.
doi: 10.7498/aps.55.3396
Abstract +
We propose a novel scheme to produce an array of micro-optical traps by using an optical system composed of a Damman grating and a spherical lens, which is illuminated by a red detuned Gaussian laser beam. We derive formulas to calculate the periodical structures of the micro-optical well arrays, and characteristics of each well, such as the spatial intensity distribution, intensity gradient, and geometrical parameters. Applications of our micro-optical traps in the fields of atom and molecule optics are briefly discussed. Our study shows that the proposed array of micro-optical wells can be used to trap cold atoms or cold molecules more efficiently than previous optical traps, even to prepare novel optical lattices.
2006, 55 (7): 3403-3407.
doi: 10.7498/aps.55.3403
Abstract +
The number of cold atoms trapped in magneto-optical trap(MOT) can be derived from probe absorption signal. After the MOT is switched off, the cold cloud freely expands in gravitational field with an initial velocity distribution. So the measurement process can be described with the interaction model between the individual stationary two-level atom and single mode resonate laser. Absorption method can largely improved the measurement precision. In this paper we introduce the physical principle of measurement and demonstrate the whole experimental procedure in detail. The number of atoms trapped in our MOT, (8±0.3)×106 is measured in experiment. And the number of steady-state atoms and the lifetime of atom trapped in MOT was used to deduce the capture rate of MOT.
2006, 55 (7): 3408-3412.
doi: 10.7498/aps.55.3408
Abstract +
The density function (B3P86) method with relativistic effective core potential has been used to optimize the structure of the ground state of BH2,BH2+ and BH2- molecules or ions,which are angular H-B-H, whose equilibrium nuclear distance and dissociation energy respectively are RBH=RBH=0.11899nm,RHH=0.21514nm，and 7.752eV; RBH=RBH=0.12896nm,RHH=0.14223nm; RBH=RBH=0.12037nm,RHH=0.21087nm. The analytic potential energy function of the ground state of BH2(2A′) has been derived by the many-body expansion theory using the equilibrium geometry structure parameters,dissociation energy and force constants,which is successfully used for describing the equilibrium geometry of BH2(2A′).
2006, 55 (7): 3413-3419.
doi: 10.7498/aps.55.3413
Abstract +
A “floating window method” is proposed to optimize the existing methods of calculating d electron occupancy in alloys from electron energy loss spectrum (EELS) with high accuracy. This method is free of some systematic errors that are serious in previous approaches. The application of this method will throw new light on the understanding of the change of d electron occupancy in alloys and the relationship between the electronic structure and properties of materials.
2006, 55 (7): 3420-3432.
doi: 10.7498/aps.55.3420
Abstract +
Geometric configurations and harmonic frequencies of AlHn(n=1—3) molecule, their univalent cation and univalent anion have been calculated by means of b3lyp and qcisd methods at 6-311++g** level with Gaussian03 software packages. Dissociation energies, first vertical ionization energies, electron affinities of the neutral molecules are studied. We compared the above theoretical values with experimental values and other theoretical values from literatures, and found that the values from qcisd method are closer to experimental values, the bond length of AlHn(n=1—3) and their univalent cation shorten with the H atom numbers increasing in AlHn molecule. That is to say, the Al atom attracts H atoms stronger as the number of the H atoms increases and electronic cloud are closer to aluminum atom. The computational results show that the equilibrium pressure of AlH3 is higher than that of NiH, but it is rather low still. For the AlH3 molecule we have the results: De=9.3705eV,ΔG0=-163.373kJ at 298.15K, so the AlH3 molecule is more stable thermodynamically. The problem is that AlH3 molecule is easier to dissociate and produce hydrogen gas. It may be stable if preserved in hydrogen gas environment.
2006, 55 (7): 3433-3437.
doi: 10.7498/aps.55.3433
Abstract +
A supersonic beam of NO molecules mixed with Ar atoms was ionized by VUV synchrotron radiation from Hefei Light Source(HLS) at National Synchrotron Radiation Laboratory (NSRL). Photoionization efficiency spectroscopy (PIES) measurement was made for NO, Ar and heterogeneous clusters Ar·NO. In PIES spectum of Ar·NO, a strong resonance peak at the position of atomic rare gas resonance lines (11.5—12.0 eV) was observed, and it is shown that the excitation energy of the rare gas atom is transferred to the attached NO molecule within a heterogeneous cluster, leading to ionization of the molecule NO.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (7): 3438-3442.
doi: 10.7498/aps.55.3438
Abstract +
Starting from the Jaynes-Cummings (J-C) model describing the interaction of a trapped ion with a standing-wave laser field, we derive the interaction Hamiltonian on the nonlinear J-C model of the trapped ion excitated resonantly with 1-quantum vibrational mode. After solving the time-dependent states of this model, we study the evolution of population inversion for the ion numerically. It is shown that the period of the quantum collapse and revival of the population inversionis related with the Lamb-Dick parameter and the position of the ion in the standing-wave laser field. With the increasing of the parameter, it will decrease the period of the collapse and revival. When moving the ion from the node of the standing-wave laser to the antinode, the period of the collapse and revival becomes longer.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (7): 3443-3450.
doi: 10.7498/aps.55.3443
Abstract +
It is a common way to obtain ion-ion plasmas from pulsed electronegative discharges. The pumping pulse can excite ion oscillation at the early active glow stage of a pulsed electronegative discharge. To study the ion oscillation and its influence on the self-sustaining condition of the discharge, a global model was developed to describe the interaction between ion oscillation and a small amount of electrons in a low-pressure ion-ion plasma. A parameter r was introduced in this model to describe the momentum residual/loss of the electrons after the collision with the electrodes. It was found a critical value r=rc that differentiates two electron loss mechanisms. Another critical value r=4rc determines two different threshold of the electron density growth. Thus, the threshold of the electron density growth is non-monotonously depend on r. Therefore, there might be a gap existing in the parameter space of the self-sustaining condition. The above result has been examined by a particle-in-cell simulation with Monte-Carlo collision (PIC-MCC).
2006, 55 (7): 3451-3457.
doi: 10.7498/aps.55.3451
Abstract +
An original DC double anode plasma torch operating with argon at atmospheric pressure which provides a long time and highly stable plasma jet is analyzed through its electrical and optical signals. Effects of gas flow rate and current intensity on the arc dynamics behaviour are studied using standard diagnostic tools such as FFT and correlation function. An increasing current-voltage characteristic is reported for different argon flow rates. It is noted that the takeover mode is characteristic for argon plasma jet and arc fluctuations in our case are mainly induced by the undulation of torch power supply. Furthermore, the excitation temperatures and electron densities of the plasma jet inside and outside the arc chamber have been determined by means of optical emission spectroscopy (OES).The criteria for the existence of local thermodynamic equilibrium (LTE) in plasma is then discussed. The results show that argon plasma jet at atmospheric pressure under our experimental conditions is close to LTE.
2006, 55 (7): 3458-3463.
doi: 10.7498/aps.55.3458
Abstract +
When the frequency of the incident electromagnetic wave is lower than that of the plasma, the high-density and low-temperature plasma column is equivalent to a good conductor. However, because of the dispersive relation and the uneven distribution of density, the wave vector propagating along the plasmas is not a real constant, but a complex quantity varying with the change in the space. So, it is hard to calculate the radiation pattern, radiation impedance and gain of the column plasma with the normal methods used with the metallic antenna. In this paper, the space distribution of the wave vectors of the signal along the column plasma is calculated from the dispersive relation of the non-magnetized columnar plasma. And then, according to the antenna equation, the radiation pattern, radiation impedance and gain of the columnar plasma with even or uneven axial density distribution can be derived. The experimental results show that the numerical values calculated by this new method are much more accurate. This method will be of great importance in the application of the plasmas in the antenna transportation.
2006, 55 (7): 3464-3469.
doi: 10.7498/aps.55.3464
Abstract +
The dielectric property of dispersive media is written as rational polynomial function, the relation between D and E is derived in time domain. It is named shift operator FDTD (SO-FDTD) method. The high accuracy and efficiency of this method is confirmed by computing the reflection coefficients of electromagnetic waves by a collisional plasma slab. The reflection coefficients between plasma and the atmosphere or vacuum can be calculated by using the SO-FDTD method.The result is that the reflection coefficients are affected by plasma thickness, electron numerical density, the distributing orderliness of electron density, and incidence wave frequency.
2006, 55 (7): 3470-3474.
doi: 10.7498/aps.55.3470
Abstract +
The JEC finite-difference time-domain (JEC-FDTD) method is extended to three dimensional anisotropic dispersive media—the magnetized plasma. The problem which incorporates both anisotropy and frequency dispersion at the same time is solved for the electromagnetic wave propagation. The three dimensional JEC-FDTD formulations for anisotropic magnetized plasma are derived. The method is applied to the electromagnetic scattering of dihedral corner reflector and sphere-cone coated with anisotropic magnetized plasma. By simulating the interaction of electromagnetic wave with magnetized plasma, some numerical results are obtained, which indicate that an appropriate plasma coating may efficiently reduce the RCS of a metallic target.
2006, 55 (7): 3475-3479.
doi: 10.7498/aps.55.3475
Abstract +
The J×B heating mechanism of plasma under the radiation of non-relativistic linearly polarized laser light is studied analytically and a self-consistent theory including the effects of two kinds of ponderomotive forces is developed. Meanwhile, the J×B heating mechanism with the density profile modification is discussed, and the relation curve of the corresponding absorption coefficient vis the laser intensity is obtained. The result shows that the absorption coefficient fabs owing to the J×B heating is about 2.8% when the laser intensity factor A0＝20.
2006, 55 (7): 3480-3487.
doi: 10.7498/aps.55.3480
Abstract +
Two groups of Sr14(Cu1-yFey)24O41 compounds with Fe3+ doping and 2/3Fe3++1/3Fe2+ admixture doping respectively were prepared by conventional solid-state reaction. X-ray diffraction analysis shows that the samples have single phase with y≤0.03 of Fe3+ doping and y≤0.02 of 2/3Fe3++1/3Fe2+ admixture doping. The lattice parameters a and b decrease gradually when the doping content increases for each group. The measurements of electronic transport properties show that the electrical resistivity decreases monotonically with the increase in y of Fe3+ doping, which indicates that free hole carriers in the ladder increase. A crossover temperature Tρ was observed in the Arrhenius plot of the resistivity versus temperature. The decrease of resistivity of the Fe3+ doped samples is interpreted in term of the dissociation of spin dimers and hole pairs located in the ladder induced by the substitution of Fe3+ for Cu2+ .Two kinds of possible conduction mechanisms above and below Tρ are presented respectively. The fitting of experimental data proves that the conduction mechanism above Tρ is due to thermal activated single-holes′ contribution, while below Tρ one-dimensional hopping conduction is dominant.
2006, 55 (7): 3488-3493.
doi: 10.7498/aps.55.3488
Abstract +
Nested wire-array is a kind of promising structured-load because it can improve the quality of Z-pinch plasma and enhance the radiation power of X-ray source. Based on the zero-dimensional model, the assumption of wire-array collision, and the criterion of optimized load (maximal load kinetic energy), optimization of the typical nested wire-array as a load of Z machine at Sandia Laboratory was carried out. It was shown that the load has been basically optimized. The Z-pinch process of the typical load was numerically studied by means of one-dimensional three-temperature radiation magneto-hydrodynamics (RMHD) code. The obtained results reproduce the dynamic process of the Z-pinch and show the implosion trajectory of nested wire-array and the transfer process of drive current between the inner and outer array. The experimental and computational X-ray pulse was compared, and it was suggested that the assumption of wire-array collision was reasonable in nested wire-array Z-pinch at least for the current level of Z machine.
2006, 55 (7): 3494-3500.
doi: 10.7498/aps.55.3494
Abstract +
In recent years, in order to cut down the production cost, substrates with large area are used in semiconductor industry, especially in the field of thin film transistor display. Obviously, the key point for the substrate fabrication needs a uniform plasma sources with large area. Among them, inductively couple plasma is one of the good candidates. In our experiments, based on a small chamber of inductively coupled plasma with a single multi-turn coil, we investigated the relationship between coil configuration and power coupling efficiency, and applied these experimental results to the generation of large-area inductively coupled plasma with parallel-connected multi-sources. By using Langmuir probe measurement, plasma parameters of this kind of large area ICP were characterized. It was shown that the large-area ICP source with parallel-connected multi-sources can produce a plasma density lager than 1010cm-3 under a rather low pressure (<10Pa). The uniformity of plasma density and the photoresist etching can be controlled to a level better than 80% by adjusting the process parameters.
2006, 55 (7): 3501-3505.
doi: 10.7498/aps.55.3501
Abstract +
Gaussian distribution models of voltage wave form of MID of TEMP Ⅱ accelerator and IPIB density near the MID focus region have been built according to the results of experiments. The energy deposited in the target were calculated by using Monte Carlo method based on these models. Then we use them as thermal sources in hydrodynamic equations, and simulate the evolution process of pressure transported in target based on different kinds of state equations of material. The pressure evolution profile of plasma generated by IPIB irradiated Al target with high enough beam energy density has also been calculated by combining the ideal gas model of plasma and HD equations.
2006, 55 (7): 3506-3513.
doi: 10.7498/aps.55.3506
Abstract +
A four-species 1-D hybrid numerical model was set up to simulate the process of formation of large-dimension plasma produced by injecting electron beams into air. It showed that plasma of the order of 0.5m in length and 1012cm-3 in density can be produced by an electron beam with the energy of 140keV and flux of 50mA/cm2. The effect of space charge associated with the beam on the beam propagation and related process vanishes soon after the plasma is produced. The beam flux is directly relevant to the plasma density, but the beam energy affects both the dimensions and the density of produced plasma.
2006, 55 (7): 3514-3518.
doi: 10.7498/aps.55.3514
Abstract +
A tape helix show wave structure is filled with uniform plasma.A dielectric is loaded inside the region between helix and a conducting waveguide.The system is immersed in a strong longitudinal magnetic field.By means of helix tape model and linear field theory,the field equations and the boundary conditions in plasma region and dielectric region are given.On the basis of the field analysis,the dispersion relation of the slow wave structure is derived and some discussions are given.
2006, 55 (7): 3519-3523.
doi: 10.7498/aps.55.3519
Abstract +
In this paper, a fluid model of electro-optic switch of plasma-electrode Pockels cells (PEPC) driven by one-pulse process is proposed. The model includes a simplified set of fluid continuity equations, Poisson's equation and the electron average energy equation, and these equations are numerically solved with the exponential difference scheme, the classical successive over relaxation method (SOR) and the classical fourth-order Runge-Kutta method, respectively. The evolving characteristics of density of charged particles, electronic temperature, electric field, discharge current, charging voltage of the KDP crystal and the switching efficiency of PEPC are simulated. The model for PEPC, which reveals the relationship between the microcosmic physical processes of gaseous discharge plasma and macrocosmic parameters of PEPC, is very useful for the design of large aperture electro-optic switches.
2006, 55 (7): 3524-3530.
doi: 10.7498/aps.55.3524
Abstract +
The effect of adding hydrogen to a nitrogen dc glow discharge is investigated by using Monte Carlo code to simulate the electron behavior in the cathode dark space (CDS). It is shown that when increasing the percentage of H2, the electron mean energy is increased, the electron density and various e-N2 collision rates are decreased, and when adding small amounts of H2 into nitrogen gas, e-N2 dissociation and electron excitation rates can be enhanced under certain discharge conditions, which will contribute to increase the density of significant active nitrogen species (N*2，N+，N) in discharge space. The hydrogen concentration is varied between 0% and 30%. These effects can be explained by the collisions taking place in the discharge. We have also compared our calculated results with experimental data.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (7): 3531-3535.
doi: 10.7498/aps.55.3531
Abstract +
The structure and magnetic properties of (Nd1-xGdx)3Fe27.31Ti1.69 compounds have been investigated by means of X-ray diffraction and magnetic measurements. All compounds with x in the range of x≤0.6 crystallize in Nd3(Fe, Ti)29-type structure. Substitution of Gd for Nd leads to a contraction of unit-cell volume. The Curie temperature TC and anisotropy field Ba of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds increases monotonically with increasing Gd content. Saturation magnetization Ms of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds decreases with increasing x. As temperature lowers from room temperature to 5K, a spin reorientation from the easy plane to the easy cone occurs for (Nd1-xGdx)3Fe27.31Ti1.69 compounds. Spin phase diagrams have been constructed for (Nd1-xGdx)3Fe27.31Ti1.69 compounds.
2006, 55 (7): 3536-3539.
doi: 10.7498/aps.55.3536
Abstract +
The structure of novel LiAlO2 crystal with Ti concentration of 0.2 at% was studied by measuring the absorption, luminescence and IR spectra. It was found that the crystal has the 196nm typical quarivalent Ti absorption peak, and also the 384nm typical quarivalent Ti emission peak when excited by 235nm light. A color-center model successfully explains the four small peaks in the range of 660—820nm, which disappeared when the samples were annealed in air or Li-rich atmosphere. Compared to the pure LiAlO2, we can find that the intensity and situation of ［LiO4］ are unchanged. Combined with the ICP results, we can count the number of Li vacancies to be about 5.5×1020 for the Ti: LiAlO2 with dimensions of 50mm×1mm.
2006, 55 (7): 3540-3545.
doi: 10.7498/aps.55.3540
Abstract +
The process of deposited energy in sensitive volumes in a static random access memory (SRAM) chip induced by 10—20MeV neutrons is simulated using the Monte Carlo method. In the simulation, the physical parameters related to the single event upset (SEU) of the SRAM chip are calculated. The results provide detailed statistical data for the SEU process induced by 10—20MeV incident neutrons, and reference information for the deface reinforcement of the SRAM chip.
2006, 55 (7): 3546-3551.
doi: 10.7498/aps.55.3546
Abstract +
The stopping power and accumulation energy for protons in SiO2 are calculated by using Monte Carlo software TRIM95. As a result, the ionizing stopping power and the nucleus stopping power are compared for protons in SiO2, and the relation between absorption dose of material surface and factual absorption dose of sensitive area is discussed. CC4007RH and CC4011 devices were irradiated with Co-60 gamma rays, 1MeV electrons and 1—9MeV protons to compare the ionizing radiation damage of the gamma rays with the charged particles. The result show that the radiation damages from Co-60 gamma rays, 1MeV electrons and 1—7MeV protons were equivalent for 0V gate bias conditions. Under 5V gate bias, the radiation damage for Co-60 gamma rays was most serious. The distinction in damage between 1MeV electrons and Co-60 gamma rays was not large. The damage from protons below 9MeV was always less than that from Co-60. The lower the proton energy, the less the damage.
2006, 55 (7): 3552-3557.
doi: 10.7498/aps.55.3552
Abstract +
Based on the molecular dynamics method and improved reactive empirical bond order potential, Green-Kubo function is used to calculate the thermal conductivity of carbon nanotube. The overlapping method is used which shortens the simulation time greatly. The result shows that the most significant contribution to the thermal conductivity is presented by the auto correlation of interactive force of atoms. The thermal conductivity decreases as the tube diameter increases. The thermal conductivity increases as the temperature increases for temperature lower than 300K and converges to a constant when the temperature rises above 300K. The thermal conductivity of the single-walled carbon nanotube ranges from 1000W/mK to 4000W/mK, and the results are in good agreement with the experimental data.
2006, 55 (7): 3558-3568.
doi: 10.7498/aps.55.3558
Abstract +
In this paper, through a systematic statistical analysis of the characteristics of the serrated yielding, including the stress drop amplitude and the drop duration, etc., the difference between the results of thinner samples (1mm and 2mm) and those of thicker samples (3mm), has been reported. The size effect in Portevin-Le Chrtelier (PLC) effect also manifests itself in the difference of PLC types of jerky flow of 1mm or 2mm thick samples and those of 3mm thick samples under the same experimental conditions. Moreover, the geometrical characteristics of attractor of the former series in phase space are described by using methods of nonlinear time series analysis, and chaotic behavior is proved to exist in these series through the application of principal component analysis. The distribution of stress drops of the latter is found to follow a power-law distribution, which is referred to as the signature of self-organized criticality phenomenon.
2006, 55 (7): 3569-3575.
doi: 10.7498/aps.55.3569
Abstract +
The serrated yielding in metals and alloys is an important and interesting physical phenomenon. No. 3004 aluminum alloy has been subjected to tension test in a range of strain rates 5.56×10-5s-1—5.56×10-3s-1 and temperatures 223K—773K to investigate the ordinary rules of serrated yielding phenomenon. The micro-mechanism and physical essence of serrated yielding of the material has been studied by means of activation energy, internal friction and microstructure. The results show that the serrated yielding phenomenon is associated with the dynamic strain aging process. In the serrated yielding temperature region, an anomalous serrated yielding phenomenon was found. Within this temperature region, a critical transition temperature Tt exists. The critical plastic strain for the onset of serrations has a negative or positive temperature coefficient within the temperature region lower or higher than Tt, respectively. The former is the normal serrated yielding and the latter is called “anomalous”. It is believed that the process at the temperature region lower than Tt is controlled by the interaction between Mg solute atom atmosphere and dislocations. In the positive coefficient region, the aggregation of Mg atoms and precipitation of second phase decrease the effective amount of Mg atoms in solid solution and leads to the appearance of a positive temperature coefficient of the critical plastic strain for the onset of serrations.
2006, 55 (7): 3576-3580.
doi: 10.7498/aps.55.3576
Abstract +
Based on the generalized gradient approximation, we have investigated the phase transition of 3C-SiC from ZB to NaCl structure using first-principles method, and obtained the accurate symmetry Imm2 (previously regarded as lower symmetry Cmm2 and Pmm2) of the intermediate phase. The relative activation enthalpy 0.647eV is close to the result of Catti. The obtained transition pressure 69GPa is lower than the experimental value of 100GPa which may be attributed to the hysteresis of the phase transition. Meanwhile, the energy bands for ZB- and NaCl-SiC were also calculated and discussed, the results suggest that the phase transition of 3C-SiC is accompanied by an electronic transition from semiconducting to metallic character besides the structure reconstruction, which may be useful for the accurate determination of the transition pressure.
Preparation and mechanism of p-type ZnO films formed by modified ion beam enhanced deposition method
2006, 55 (7): 3581-3584.
doi: 10.7498/aps.55.3581
Abstract +
In-N codoped ZnO films were prepared on Si and SiO2/Si substrates by modified ion beam enhanced deposition method. ZnO mixed with 2 atm % In2O3 powder was used as sputtering target and during the deposition N+/Ar+ mixed beam was implanted into the deposited films. The XRD results showed that all polycrystalline In-N codoped ZnO films deposited on Si and SiO2 substrates have a preferred (002) orientation and showed p-type conduction. The as-deposited films were annealed in N2 and O2. After annealed in N2 the lowest resistivity of p-type In-N codoped ZnO films was 0.9Ωcm. The dependence of film structure and electrical properties on deposition and annealing condition were discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (7): 3585-3589.
doi: 10.7498/aps.55.3585
Abstract +
Electrical structures and optical properties of β-Si3N4 have been calculated by means of plane wave pseudo-potential method (PWP) with GGA. The results such as lattice constants and band structures are in good agreement with experimental data. Furthermore, the pressure-dependent coefficient and band gap of β-Si3N4 have also been calculated, which will be helpful in the application of Si3N4 under high pressure.
2006, 55 (7): 3590-3596.
doi: 10.7498/aps.55.3590
Abstract +
In order to study 2D metallic photonic crystal, a new plane-wave expansion method was proposed. Based on traditional plane wave expansion method, the “original problem” to be solved was extended to a “new problem”. First, the relation between them were given, second, the “new problem” was transformed to an integral-differential eigen equation through an auxiliary function. The eigen equation was solved to obtain the band gap structures of the “new problem”. The band gap structures of the “original problem” were deduced according to “new problem”. Finally, numerical computations were done for 2D square-lattice square metallic rods photonic crystal, and excellent results were achieved.
2006, 55 (7): 3597-3600.
doi: 10.7498/aps.55.3597
Abstract +
The electron structure of barium's VIB compound is not clearly known yet. The main problem is that not only the band gap calculated by using DFT (density functional theory) has a large discrepancy compared with experimental results,but also the theoretical values of band gap are inconsistent for different research groups.In order to resolve these problems, this paper makes the Green function-screened coulomb interaction quasiparticle theory(GW) calculation to get the quasiparticle band structure of BaSe.For the convenience of comparison, it deals with the systematic calculation of the energy band of BaSe by using the methods of local density approximation (LDA) and the generalized gradient approximation(GGA). The result shows that the methods LDA and GGA can not describe the band gap of the material accurately, because the calculation errors are as high as 39.9% and 32.6%, respectively. However, the result of quasiparticle band gap by GW improves the band gap value greatly and give the theoretical result which agrees with the experimental measurement. At variance with the known result, BaSe of quasiparticle band gap in the B1 structure is shown to have a direct gap at the Γ-point in the present paper,which indicates that it is important to take into account the 4d electronic effect in the valence electron configuration of barium.
2006, 55 (7): 3601-3605.
doi: 10.7498/aps.55.3601
Abstract +
The geometric and electronic properties of the three isomers for C72 and La2@C72 have been studied using the generalized gradient approximation in density functional theory (DFT). It is found that C72(D6d) which satisfies the isolated-pentagon rule is the most stable structure among the three isomers of C72, while La2@C72 (#10611) is the most stable structure and La2@C72 (D6d) is the most unstable structure among the three isomers of La2@C72. It is also found from the analysis of energy levels as well as the density of states that the stability change is due to the mixing of La atomic orbital with C atomic orbital in C72. From Milliken populations, we find that there are about three electrons transferring from the two encaged La atoms to C72 cage so the electronic configuration of La2@C72 (#10611) can be described as La3+2@C3-72. We also come to the conclusion from the net spins of La as well as of La2@C72 that the magnetic moments of La have been completely quenched so La2@C72 (#10611) shows no magnetism.
2006, 55 (7): 3606-3610.
doi: 10.7498/aps.55.3606
Abstract +
Patterned c-plane sapphire substrate is prepared by chemical etching. GaN films are grown by LP-MOCVD on surface treated sapphire substrate and common c-plane sapphire substrate. The structure and properties of the GaN films are analyzed by high-resolution double crystal X-ray diffraction(DCXRD), scanning electron microscope(SEM) and atomic force microscope(AFM).The results indicate that the quality of GaN film grown on sapphire substrate prepared by surface treatment is superior to that grown on common c-plane sapphire substrate. High-resolution double crystal X-ray diffraction shows that for the GaN grown on surface treated sapphire substrate,the (0002) and (1012) reflections have full-width at half-maximum as low as 208.80arcsec and 320.76 acrsec, respectively. The shortcomings of procedure complexity and high crystallographic tilt in conventional lateral epitaxial overgrowth are overcome by using the new method.
2006, 55 (7): 3611-3616.
doi: 10.7498/aps.55.3611
Abstract +
In this paper, the band profiles of HgCdTe (MCT) heterojunctions with the configuration of wide/narrow gap-p on narrow/wide gap-n are calculated, respectively. In the theoretical model employing a valence band offset, a new simple carrier density approximation is proposed to include the carrier degeneracy and conduction band non-parabolicity in the calculations. The effects of the location of p-n junction (zB) and the interface charge density (Q) on the band profiles of MCT heterojunctions are studied systemically, which is found to be significant and can't be neglected. With the help of the results of above research, the optimal design related to zB and Q is obtained.
2006, 55 (7): 3617-3621.
doi: 10.7498/aps.55.3617
Abstract +
In view of the specific properties of InP-based composite channel High Electron Mobility Transistor(HEMT),we made a correction to the traditional single channel HEMT and promote a new small signal physical model which can be applied to composite channel HEMT.The commercial device simulation program-ISE(Integrated Systems Engineering) has been used to simulate and verify this new model. We have compared the measured and simulated Hemt's I-V and transference characteristics, The change of electric field and electric current density in InGaAs/InP composite channel when quantum effect is taken into consideration are studied, The results show that due to quantum effect in InGaAs channel,in the area under the gate and near the source where electric field is low, current flow is distributed mostly in the InGaAs channel,while in the area under the gate and near the drain where electric field is high ,current flow is distributed mostly in the InP channel.Under different gate voltages ,the current flow shows different proportions in both InGaAs and InP channel. The new model is proved to be valid.
2006, 55 (7): 3622-3628.
doi: 10.7498/aps.55.3622
Abstract +
As the most remarkable effect in GaN microwave power device, Current slump has been studied widely.However,there still exist unsolved proplems.Based on the analysis of experiment and theory on the AlGaN/GaN high electron mobility transistor (HEMT) under dc sweep,an analytical model for the current collapse is developed considering the effects of polarization and surface states.The comparison between simulations and physical measurements shows a good agreement.
2006, 55 (7): 3629-3635.
doi: 10.7498/aps.55.3629
Abstract +
In this article a first-principles total energy calculation of the atomic geometry and electronic structure of carbon-monoxide and hydrogen co-adsorbed on Ni(111) p(2×2) surface at a coverage of 0.25 ML is reported. The optimized atomic geometry is in good agreement with the most recently reported LEED experiment on Ni(111) p(2×2)/(CO+H) co-adsorbed system. The carbon-monoxide is predicted to be adsorbed on the hcp site while hydrogen atom occupies the fcc site, and both adsorbates locate on opposite p(1×1) cells within a p(2×2) supercell. The adsorption energy of CO and H in this configuration is 2.81 eV with respect to the CO and H2 molecule and the surface work function is calculated to be 6.28 eV in comparison with 5.23 eV of clean Ni(111) surface. The bond lengths of C—O, C—Ni, and H—Ni are estimated to be 1.19?, 1.96?, and 1.71?, respectively, and the substrate interlayer distance variations, Δd12 and Δd23, are calculated to be +1.6% and +0.4%, respectively. The chemisorptions of CO and H atom on the Ni(111) p(2×2) surface were calculated in the same way and the adsorption heights of CO and H were evaluated to be 1.33? and 0.90?, respectively. The interaction energy between CO and H in the best fit geometry of Ni(111) p(2×2)/(CO+H) system is about 0.60 eV, which could be taken as the essential factor for the realization of Fisher-Tropsch reaction.
2006, 55 (7): 3636-3641.
doi: 10.7498/aps.55.3636
Abstract +
Dilute GaNxAs1-x thin films with N concentration from 0.0% to 3% have been grown by molecular beam epitaxy. Piezomodulated reflectance (PzR) spectra of these thin films have been measured at room temperature, and optical transitions in PzR spectra have been well resolved. The N-related transition of E1+Δ1+ΔN had been observed in PzR spectrum of GaN0.005As0.995 and GaN0.01As0.99 films. The well resolved split between heavy hole and light hole of Γ valence band is shown in PzR when the N doping level is up to 1%. The N concentration dependence of transition energies supports the model that both E+ and E* originate from the L conductive band at room temperature.
2006, 55 (7): 3642-3648.
doi: 10.7498/aps.55.3642
Abstract +
Because of the isotropic energy band structure of the Γ electrons in the GaAs/AlGaAs quantum well infrared photodetector (QWIP), normal incident radiation absorption is forbidden, so that the optimization of optical grating becomes a key technology. In this work we present a scattering-matrix method based on plane-wave expansion for the two-dimensional QWIP grating. The transmission spectrum of the QWIP grating has been studied theoretically and experimentally. It has been shown that in general, both the propagating wave and the evanescent wave contribute to the optical coupling in n-type QWIP. The grating parameters, like period, depth and filling factor, will strongly affect the optical coupling.
2006, 55 (7): 3649-3655.
doi: 10.7498/aps.55.3649
Abstract +
Within the framework of effective-mass approximation, the properties of the localized electronic states in a N-layer superlattice (SL) with structural defects in finite magnetic fields are investigated by utilizing the transfer matrix and effective barrier-height methods. When the mismatch of electron effective mass in different constituent layers is considered, an external magnetic field will lead to the magneto-coupling. The numerical results show that the magneto-coupling brings about not only quantization of localized electron levels but also the degree of the strong dependence of the localized levels on Landau indices and magnetic fields, especially for the localized levels in higher energy region. In addition, we demonstrate in detail the correlations between the localized electronic states inside the minigaps of the infinite SL with structural defect layer and the resonant transmission peaks in dips of the finite SL. A good coincidence between the localized states and transmission peaks is found, which provides a theoretical basis for experimental observation of the localized electronic states in SLs.
2006, 55 (7): 3656-3663.
doi: 10.7498/aps.55.3656
Abstract +
2D analytic models for the electric field distribution of charge imbalance SJ structures, such as concentration and width imbalance, trapezoid n-/p- regions and lateral linearly graded doping have been presented. The comparison of the 2D analytic model with numerical device simulations shows that the proposed model can accurately predict electric field distribution. Although this solution is in the form of trigonometric series, some most important information also can be obtained from this solution. For example, the peak electric field and breakdown voltage in charge imbalance SJ structure can be obtained from the results of this paper.
2006, 55 (7): 3664-3669.
doi: 10.7498/aps.55.3664
Abstract +
Fe-Ni-BaTiO3 three-phase composites with super high dielectric constant were successfully prepared by sintering BaTiO3 with various amount of metal (Ni and Fe with a fixed mol ratio of 78∶22) in nitrogen atmosphere at 1250℃ for 2h. The impedance and the dielectric properties were measured by an Agilent 4294A precision impedance analyzer, and the dc conductivity was measured by a Keithley 6571 high resistance meter. The results indicate that this type of composite undergoes an insulator-conductor transition with increasing metal concentration and the dielectric constant diverged near the percolation threshold. The dielectric constant reaches as high as 22000 when fMetal=0.23, which is about 12 times that of the BaTiO3 matrix, while the dielectric loss keeps still a low and stable value of about 0.08 with increasing metal concentration. And the dielectric relaxation shows a notable Maxwell-Wagner characterization, which suggests that conduction mechanisms may play an important role in the dielectric response.
2006, 55 (7): 3670-3676.
doi: 10.7498/aps.55.3670
Abstract +
A threshold condition different from the classical one is proposed for MOSFET with quantum effects, by means of self-consistent numerical solution of the Schrdinger's and Poisson's equations, and thus an accurate 1-D threshold-voltage model is obtained with good agreements between simulated results and measurement data. Based on this 1-D model, an accurate 2-D quantum-modified threshold-voltage model for small-scale MOSFET is developed by solving the quasi-2D Poisson's equation and taking short-channel effects and quantum-mechanical effects into consideration. The model can also be used for simulation of electrical properties and design of structural parameters for deep-submicron MOSFETs with high-k materials as gate dielectric.
2006, 55 (7): 3677-3682.
doi: 10.7498/aps.55.3677
Abstract +
The principle of high-electron-mobility transistor (HEMT) and the property of two-dimensional electron gas (2DEG) have been analyzed theoretically. The concentration and distribution of 2DEG in various channel layers are calculated by numerical method. Variation of 2DEG concentration in different subband of the quantum well is discussed in detail. Calculated results show that sheet electron concentration of 2DEG in the channel is affected slightly by the thickness of the channel. But the proportion of electrons inhabited in different subbands can be affected by the thickness of the channel. When the size of channel lies between 20—25 nm, the number of electrons occupying the second subband reaches the maximum. This result can be used in parameter design of materials and devices.
2006, 55 (7): 3683-3687.
doi: 10.7498/aps.55.3683
Abstract +
We used a time-dependant Ginzburg-Landau modified model to calculate the model under pressure. We obtained some expressions for the relation between the external pressure and the temperature of superconductivity. In some special cases, the critical temperature decreases with applied pressure. In some other cases, the critical temperature increases with applied pressure.
2006, 55 (7): 3688-3691.
doi: 10.7498/aps.55.3688
Abstract +
The ground-state properties of spin-Peierls ladder model with interchain Heisenberg interaction and interchain Dzyaloshinskii-Moriya(DM)interaction are studied by Lanczos numerical method. We mainly concentrate on the influence of interchain Heisenberg interaction and interchain DM interaction on system dimerization. The results show that these two interchain interations always act against the dimerization of the system, and they can make system ground state dimerization diminishing, which means that increasing the system dimensions may reduce system dimerization, even destroy the dimerization phase.
2006, 55 (7): 3692-3697.
doi: 10.7498/aps.55.3692
Abstract +
The magnetic transition and conducting behaviors of LaMn1-xCuxO3 (x=0.05, 0.1, 0.2, 0.3, 0.4) system have been systematically studied. The results show that very small amount of Cu-doping (x=0.05) into the anti-ferromagnetic LaMnO3 matrix induces strong ferromagnetic transition below about 157K. The Curie temperature decreases gradually with the increase of Cu-doping content, while the magnetization increases firstly and then decreases. In accordance with the magnetic properties, the electrical resistivity decreases at low dopant (x≤0.10) and then increases with the increase of Cu-doping content. All samples exhibit insulating conducting behavior in the whole temperature range: from a paramagnetic insulator to a ferromagnetic insulator. The conducting behavior of lower doped samples (x≤0.10) is well fitted by the Mott Variable Range Hopping (VRH) model,and then favors to the thermoactivation model when 0.10≤x≤0.40. With the increase of Cu-doping content, the influence of Cu ions on the double exchange interaction among the Mn-O-Mn chains and the magnetic structure results in that the eg electron transport obeys the domination of potential barrier in the VRH model at lower doping and then favors the domination of energy gap in the thermal activation model at higher doping contents.
2006, 55 (7): 3698-3704.
doi: 10.7498/aps.55.3698
Abstract +
The detailed expressions of orientation-related relative permeability in amorphous alloy ribbons and films with in-plane nearly transverse uniaxial anisotropy under applied driving ac current flowing through the ferromagnetic materials and dc external magnetic field are derived by simultaneously solving the Maxwell's equations and the Landau-Lifshitz equation of motion and establishing the magnetic domain structure model. The calculation formula of mean relative permeability averaging over 90°orientation angle and the magneto-impedance are obtained. The relation between permeability and the component of tensor susceptibility is deduced. The dependences of the real part and imaginary part of the relative permeability on frequency at several values of the applied external field are calculated, and the corresponding magnetic permeability spectra are plotted. The calculation formula of permeability which were inferred by Panina et al and Kraus can be unified by our theoretical result which is in good agreement with the experimental data under lower external magnetic field for both amorphous ribbons and films.
2006, 55 (7): 3705-3710.
doi: 10.7498/aps.55.3705
Abstract +
In this work, the polarization of the ferroelectret was first estimated based on the experimental results of charging current by a corona charging with a grid in combination with the reverse-polarity corona charging compensation method. The experimental results indicated that the polarization drastically increases with the rise of grid voltage accompanying the breakdown of gas in the void. Also, by means of the charging method mentioned above and analyzing the thermally stimulated discharging spectra, the charge dynamics of macroscope dipoles with space charges and their compensation charges near the free surface of the film during thermal depolarization were discussed. A geometric distribution of trap levels trapping two kinds of charges was discovered, that is, the space charges formed in the macroscopic dipoles were trapped in shallow- and deep- energy level traps respectively, while the space charges located near the free surface of the film were trapped in medium energy level traps.
2006, 55 (7): 3711-3715.
doi: 10.7498/aps.55.3711
Abstract +
Na0.25K0.25Bi0.5TiO3(NKBT50)lead-free ceramics were prepared by solid-state reaction. The dielectric property of the ceramics was investigated in the lemperature range from room temperature to 400℃. Our results show that there exists a dielectric anomaly in the vicinity of 70℃ for the unpoled ceramics sintered in air, which will disappear after the ceramic were poled or sintered in oxygen. It is believed that the dielectric anomaly is caused by defect dipoles related to oxygen vacancies. Thermal stimulated depolarization current shows that the materials are depolarized at 225℃ and the dielectric anomaly corresponding to this phase transition is also affected by oxygen vacancies.
2006, 55 (7): 3716-3720.
doi: 10.7498/aps.55.3716
Abstract +
The ferroelectric ceramics samples of SrBi4-x/3Ti4-xMoxO15(x=0.00, 0.003, 0.012, 0.03, 0.06, 0.09) have been prepared by the conventional solid-state reaction method. X-ray diffraction analysis shows that the crystal structure of SrBi4Ti4O15 (SBTi) is not affected by Mo-doping. The scanning electronics microscope (SEM) images indicate that all the samples consist of sheet grains and the grain size is reduced by Mo-doping while the ferroelectric properties are improved significantly. The remanent polarization (2Pr) increases at first，then decreases with the increasing Mo content. At x=0.06, the 2Pr maximizes at a value of 26.5 μC/cm2, which about 117% higher in comparison with that of SBTi. And the coercive field of SBTi is increased only about 20%. The Curie temperature of the samples varied slightly after doping, which implies that the good thermal stability of SBTi is not sacrificed.
2006, 55 (7): 3721-3724.
doi: 10.7498/aps.55.3721
Abstract +
To explain the fast motion of ferroelectric-paraelectric interface, a mechanism based on latent heat release and conduction has been introduced. Its finite-size effect shows that the velocity of interface motion increases with decreasing system thickness. The theoretical results agree with experiments.
2006, 55 (7): 3725-3729.
doi: 10.7498/aps.55.3725
Abstract +
A series of one-dimensional disordered photonic crystals were designed for use as filters. We prepared the filters experimentally and measured the transmission characteristic of the filters by using infrared spectrometer. The experimental results are in agreement with the calculation results.
2006, 55 (7): 3730-3735.
doi: 10.7498/aps.55.3730
Abstract +
Au/SiO2 nano-composite multilayer thin films were prepared by magnetron plasma sputtering. The effect of microstructure on the absorption spectra of films of the same thickness but under different deposition conditions, and films deposited under the same conditions but having different thicknesses was investigated. The results show that the optical absorption peaks appeared at 560 nm for the Au/SiO2 nano-composite multilayer films, the intensity of the absorption peak increased with increasing Au content and thickness of films. No nano-multilayer structure and absorption peak was observed when Au particle connected together due to high Au content. The optical absorption spectra of Au/SiO2 multilayer thin films well agree with the theoretical optical absorption spectra calculated from modified Maxwell-Garnett effective medium theory.
2006, 55 (7): 3736-3742.
doi: 10.7498/aps.55.3736
Abstract +
Carbon nanotubes coated with an nonlinear optical (NLO) polymer, poly［3-hexylthiophene-2,5-diyl］-［3-methoxyl-4-hydroxyl-benzylidenequino-methane］(PHTHMOBQ/MWNTs), were synthesizedvia in-situ polymerization. The micrograph of PHTHMOBQ/MWNTs has the coaxial tubular structure, which indicated that the polymer was restricted and wrapped on the surface of carbon nanotubes while propagating during polymerization. PHTHMOBQ/MWNTs showed fluorescence quenching, which involved the inter-molecular photo-induced charge transfer process. Third-order nonlinear susceptibility χ(3) and second-order hyperpolarizability γ of PHTHMOBQ/MWNTs were measured using degenerate four wave mixing at 532nm under nanosecond pulse excitation. The two pump beams were vertically polarized and the probe beam was horizontally polarized to avoid thermal effect. The third-order NLO responses were enhanced gradually when nanotube content increased, which was attributed to inter-molecular photo-induced electron transfer between PHTHMOBQ and MWNTs.
2006, 55 (7): 3743-3747.
doi: 10.7498/aps.55.3743
Abstract +
Positron annihilation lifetime spectroscopy and Fourier transform Infrared spectrometer were used to study the effect of γ irradiation dose on free volume and microstructure of polystyrene-block-butadiene diblock copolymer, respectively. Based on the free volume classic model of Eldrup and examonation of the correlation between their results, the model of γ irradiation effect on cross-linking and degradation of SB is established. Thermal gravity analysis was used to study thermal stability of SB at various irradiation doses to reveal the relationship between thermal stability and micro-structure changes.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (7): 3748-3755.
doi: 10.7498/aps.55.3748
Abstract +
Diamond-like carbon (DLC) films were prepared on copper substrate through preparation of intermediate layers by combined plasma enhanced sputtering physical vapor deposition and microwave electron cyclotron resonance plasma enhanced chemical vapor deposition techniques. Raman spectroscopy indicated that the films had amorphous structure and typical characteristic of DLC film. With the increase of deposition bias voltage, D and G band both shifted to high wave-number and ID/IG increased gradually. The morphology was characterized by atomic force microscopy (AFM) and the results indicated that the films were dense and homogeneous , and the roughness of the films decreased with the increase of the deposition bias voltage. Hardness and modulus of DLC were measured by the nanoindentation.
2006, 55 (7): 3756-3759.
doi: 10.7498/aps.55.3756
Abstract +
Poly-SiGe films were prepared by a metal-induced growth technique with ultrahigh vacuum chemical vapor deposition(UHVCVD) at low temperature. The crystal quality and morphology of poly-SiGe films were characterized by XRD and SEM. The influences of varying the thickness of Ni prelayer and the growth parameters on poly-SiGe films were investigated. It is shown that thicker Ni(≥10nm) has an obvious effect on poly-SiGe growth at 420—500℃. And for the samples with 60nm thick Ni layers, poly-SiGe deposition yields a continuous, highly crystalline film with good morphology.
2006, 55 (7): 3760-3765.
doi: 10.7498/aps.55.3760
Abstract +
ZnO nano-bulk materials with high density and low brittleness is prepared on CS-1B 6×8000kN cubic high pressure apparatus. Grain sizes and microstructures of the samples have been characterized by X-ray diffraction and field emission scanning electron microscopy. The Raman spectra of polar semiconductor ZnO are studied by Raman spectrophotometer in the range of 50—500cm-1. No obvious size confinement effect is found in the polar semiconductor oxide.
2006, 55 (7): 3766-3771.
doi: 10.7498/aps.55.3766
Abstract +
The magnetoelectric effect can be observed in the composites of magnetostrictive and piezoelectric phases by the the mechanical transfer from one to the other. The large magnetoelectric effect exists in the multiferroic composites with Pb(Zr,Ti)O3 rod arrays embedded in a ferromagnetic medium of (Tb,Dy)Fe2/epoxy. The large magnetoelectric effect and its origin in this structure was discussed on the basis finite element method. The numberical results were close to that of the experiment. The distributions of strain, stress and electric polarization and their relation were analyzed. The authors gave a way to improve the magentoelectric effect based on the distribution of the electric polarization.
2006, 55 (7): 3772-3777.
doi: 10.7498/aps.55.3772
Abstract +
The composites of polyaniline/multi-walled carbon natotubes (PANI/MWCNT) were prepared by electrostatic interaction between MWCNT and aniline via in situ polymerization. The results of Fourier transform infrared spectroscopy, Raman spectroscopy and ultraviolet-visible absorption spectroscopy indicated that aniline molecules were adsorbed and polymerized on the surface of MWCNTs. The composite dimensions were observed by scanning electron microscope and transmission electron microscope, the diameter of PANI/MWCNT was measured to be about 40—70 nm, and the thickness of the coated polyaniline was about 15—20 nm. Third-order optical nonlinear susceptibility of PANI/MWCNT composites were measured by degenerate four-wave mixing. The results showed that the resulting PANI/MWCNT composites exhibited larger third-order optical nonlinear susceptibilities than that of pure PANI, which can be ascribed to the π-electron coupling between the PANI and the MWCNTs.
2006, 55 (7): 3778-3784.
doi: 10.7498/aps.55.3778
Abstract +
The effect of an applied magnetic field on the growth patterns of Zn electrodeposits on filter paper was investigated using an optical microscope and an atom force microscope. It was found that the concentration of electrolyte and the fibre of filter paper influenced strongly the morphology of Zn electrodeposits obtained in unsaturated electrolyte. No evidence indicated that the magnetic field affected the morphology of electrodeposits obtained in unsaturated electrolyte. The branches of Zn electrodeposits obtained in saturated electrolyte grew in two layers, and the thin layer that adhered to the filter paper grew faster than the thick layer. In the case of saturated electrolyte, the 0.40T magnetic field made the branched electrodeposits grow into a spiral pattern. On the basis of these experimental results and the related theories, it was proposed that the magnetic field influenced the morphologies of the branched Zn electrodeposits grown on filter paper through the Hall effect.
2006, 55 (7): 3785-3788.
doi: 10.7498/aps.55.3785
Abstract +
Well-aligned and highly ordered nano-hole array copper membranes were copied from anodic aluminum oxide (AAO) template by vacuum plating. SEM shows that the nanoholes of copper membranes are hexagonally arranged with high regularity consistent with that of AAO template. The mean diameter of the holes was dependent on the corresponding parameter of AAO template. Compared with AAO membranes, the nano-hole array metal ones have many advantages in better chemical and thermal stability and higher mechanical strength, and are likely to play an important role in nano-copy field.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (7): 3789-3795.
doi: 10.7498/aps.55.3789
Abstract +
The calculation of radiative energy flux is very important in the study of diffusive supersonic wave transfer when the radiative thermal conduction approximation is used. In this paper, a formula of radial position-dependent spectral energy flux is given for the diffusive supersonic wave in a low density filled cylinder with a high density wall. A geometrical factor is defined to describe the influence of the radial size of the cylinder on the radiative energy flux. From the formula, the geometrical factor decreases with the radial position from center to edge, due to the much shorter mean free path in the wall than in the fill. This is another important reason in causing a significant curvature in the radiation front, which was observed in recent diffusive supersonic wave experiments. In addition, expressions for calculating the averaged spectral energy flux over the cylinder cross-section and the energy flux in local thermal equalibrium are given. The geometrical factor in the expression of the averaged spectral energy flux is compared with the conventional geometrical factor obtained via geometrical free path which people usually used in their simulation. Finally, to make the simulation easy, approximate expressions are given for the geometrical factors.
2006, 55 (7): 3796-3798.
doi: 10.7498/aps.55.3796
Abstract +
In this paper the tunneling framework is adopted to investigate the Hawking radiation. The emission rate which massive particles tunnel across the event horizon of the Schwarzschild black hole is calculated. It is consistent with an underlying unitary theory and takes the same functional form as that of massless particles.
