Vol. 55, No. 11 (2006)
2006-06-05
GENERAL
2006, 55 (11): 5575-5578.
doi: 10.7498/aps.55.5575
Abstract +
The simulated and measured electric field distributions along the separated function radio frequency quadrupoles(SFRFQ) are presented in this paper. Based on the simulations, the parameters of flake-electrode and the effective gap voltage gain have been optimized. As a design example, one set of SFRFQ electrode with 5 periods and inter-electrode voltage 70 kV is designed to accelerate O+ from 1MeV to 1.5MeV.
2006, 55 (11): 5579-5584.
doi: 10.7498/aps.55.5579
Abstract +
By using the function and equation transformations,a coupled linear second-order differential equations are reduced to a nonlinear first-order Elliptic equation. And the analytical solutions to coupled transformations that include first-order and second-order transformations are given.The special approximate solution to a superconductivity question derived from a reference is reformed by using the new result given in this paper, and the existence of electric field in the surface of superconductor is validated.
2006, 55 (11): 5585-5589.
doi: 10.7498/aps.55.5585
Abstract +
A general approach to the construction of conservation laws for nonholonomic nonconservative dynamical systems in the event space was presented. Firstly, the differential equations of notion of systems are written, and the definition of integrating factors is given. Next, the necessary conditions for the existence of the conserved quantities are studied in detail. Finally, the existence theorem and its converse of conserved quantities for the nonholonomic nonconservative dynamical systems in the event space are established, and an example is given to illustrate the application of the result.
2006, 55 (11): 5590-5593.
doi: 10.7498/aps.55.5590
Abstract +
The purpose of this paper is to study local energy integral for the Birkhoffian systems. The condition under which there exists the integral in the Birkhoffian systems is obtained. Two examples are given to illustrate the application of the result.
2006, 55 (11): 5594-5597.
doi: 10.7498/aps.55.5594
Abstract +
The Mei symmetry, i.e. the form invariance, of an Emden system is studied. The definition and determining equation of Mei symmetry in the Emden system are given. The relations between the Mei symmetry,the Lie symmetry and the Noether symmetry are studied, and the conserved quantities of the Emden system are obtained. An example is given to illustrate the application of the results.
2006, 55 (11): 5598-5605.
doi: 10.7498/aps.55.5598
Abstract +
Symmetry theory of the generalized Hamilton-Tabarrok-Leech’s canonical equations is presented. The differential equations of motion of systems are written. The Noether symmetry, the form invariance and the Lie symmetry of systems are studied, and the corresponding conserved quantities are found. Finally, an example is given to illustrate the application of the results.
2006, 55 (11): 5606-5610.
doi: 10.7498/aps.55.5606
Abstract +
Seeking for higher-dimensional integrable models is important in nonlinear science. By using the infinite dimensions Virasoro symmetry subalgebra［σ(f1),σ(f2)］=σ(f′1f2-f′2f1) and prolongation theory, many higher-dimensional models can be derived. By means of a concrete realization, some higher-dimensional differential integrable models with infinite dimensions Virasoro symmetry subalgebra can be obtained. In this paper, this method is extended to obtain differential-difference models and a (3+1)-dimensional Toda-like lattice which is week multi-linear variable separation solvable (MLVSS) model is derived. In addition, this model can be symmetry reduced to a (2+1)-dimensional special Toda lattice which is a MLVSS model. A (1+1)-dimensional MLVSS Toda lattice also can be obtained. Because some arbitrary functions are included, abundant new localized excitations such as dromion solution, lump solution, ring soliton, breather instanton et al can be found by selecting appropriate functions.
2006, 55 (11): 5611-5616.
doi: 10.7498/aps.55.5611
Abstract +
Using an entended Riccati mapping approach, we discuss the related Schr?dinger system and obtain the new exact solutions. Based on the derived solutions, the soliton-impulse and temporal-soliton and the interaction between solitons were constructed in this paper.
2006, 55 (11): 5617-5622.
doi: 10.7498/aps.55.5617
Abstract +
By constructing two new Riccati equations and using the generalized Riccati method, we simplified the form and enriched the general results.Using Mathematica software, exact solutions of the variable coefficient combined KdV equation with forced term are obtained, including many kinds of solitary-wave-like solutions,guasi-periodical solutions and solitary wave solutions with variable speed.
2006, 55 (11): 5623-5628.
doi: 10.7498/aps.55.5623
Abstract +
In this paper, we exploit two-mode model to investigate the influence of quantum fluctuation on the self-trapping of the Bose-Einstein Condensate(BEC). We found that, even for the finite number of particles, the transition to self-trapping is still observed.In particular, because of the quantum fluctuation due to the finite number of particles, the critical phenomenon becomes fuzzily: the smaller the number of particles is, the more obviously fuzzily the critical phenomenon becomes. Quantum entanglement entropy is then introduced to depict the critical behavior near the transition point.
2006, 55 (11): 5629-5637.
doi: 10.7498/aps.55.5629
Abstract +
Antisymmetrizing the actions of hand triple contained in volume operator and grasping on the segments rooting through any-valent vortex of spin netwok, and using the binor identity, a proof is given that all these actions are eigenactions with eigenvalue -2. A systematic algebraic method to calculate the eigenvalues of volume operator for any-valent vortices is given, and the general and algebraic expressions of volume eigenvalues for 3-, 4-, 5-, 6- valent vertices are obtained.
2006, 55 (11): 5638-5642.
doi: 10.7498/aps.55.5638
Abstract +
The thermodynamic quantities of massless scalar, neutrino, electromagnetic, massless Rarita-Schwinger and gravitational fields near the general spherically symmetric static black holes are investigated by using the modified equation of state density due to the generalized uncertainty relation. It is shown that the thermodynamic quantities depend not only on the characteristic of the black hole but also on the spin of the fields and the size of minimal length.
2006, 55 (11): 5643-5647.
doi: 10.7498/aps.55.5643
Abstract +
By evaporative cooling in QUIC trap, Bose-Einstein condensate (BEC) was achieved with 2×105 87Rb atoms in |F=2, mF=2〉 state. We have demonstrated the criterion of BEC transition by the variation of the axial size of the atoms in tight confinement, and observed phase transition from thermal atomic gases to Bose-Einstein condensate, and measured the shift of aspect ratio of BEC during free expansion, which compared with theoretical prediction.
2006, 55 (11): 5648-5656.
doi: 10.7498/aps.55.5648
Abstract +
In this paper, a simple infinite dimensional system (time-delayed van der Pol’s electromagnetic system) with rigorous solution is developed. Based on Poincaré mapping of the right-traveling voltage wave at the left end of the transmission line (x=0), the phenomena of bifurcations and chaos are investigated with the variation of system parameters E and λ. Numerical results show that there are very complex nonlinear dynamical behaviors in this time-delayed system, such as attractor co-existing, intermittent chaos, quasi border collision bifurcation to chaos and period-adding phenomena. In the meantime of studying the temporal chaotic behaviors, the spatial chaotic behaviors are preliminarily analyzed. Through depicting spatial distribution profile of the voltages, the different spatial patterns are observed in the time-delayed van der Pol’s electromagnetic system with the variation of system parameters E and λ, such as chaos, period and so on.
2006, 55 (11): 5657-5666.
doi: 10.7498/aps.55.5657
Abstract +
Based on a simple infinite dimensional electromagnetic system consisting of a linear lossless transmission line in combination with a nonlinear boundary condition, the local map of backward voltage wave is established by using the traveling wave theory. The numerical simulation results show rich spatiotemporal nonlinear phenomena in the voltage wave on the lossless transmission line. The pattern dynamics in spatiotemporal chaos of the voltage wave on the lossless transmission line are qualitatively analyzed by depicting space-amplitude plot and space-time diagram. A good model with solution is established to study and understand the spatiotemporal chaos.
2006, 55 (11): 5667-5673.
doi: 10.7498/aps.55.5667
Abstract +
EMI of the switching-converter is decided by the spectrum of the PWM waveform. There is great theoretical and practical meaning to quantify and analysis them. This paper takes the PWM drive waveform as a time series of processes or events. Based on the analysis of the periodic frequency- spreading, statistical theory is applied to analyze the probability density function, characteristic function, invariable distribution and power spectral density of the PWM waveform under chaotic frequency-spreading, the characteristics of chaotic frequency-spreading are obtained. Finally, some feasible experiments are carried out which verified that the EMI of the switching converters is suppressed effectively by chaotic frequency-spreading.
2006, 55 (11): 5674-5680.
doi: 10.7498/aps.55.5674
Abstract +
The role of inhibitory self-connection in a second order recurrent neural network with delays has been investigated. A sufficient condition is proposed to guarantee the global asymptotical stability of the equilibrium point for the delayed neural network. The results indicate that an unstable neural network without inhibitory interconnections can be asymptotically stabilized to a unique equilibrium point via embedding inhibitory self-connections with proper strengths, and the role of inhibitory self-connections will be restricted by the magnitude of transmission delays. Two simulation examples are used to show the effectiveness of the obtained result.
2006, 55 (11): 5681-5687.
doi: 10.7498/aps.55.5681
Abstract +
Based on Lyapunov stability theory, a new method combining feedback control and adaptive control is proposed for the synchronization between two different chaotic systems. This method can be applied to solve synchronization problems of several classes of chaotic systems, e.g., Lorenz system, Chen system, Lü system, Liu system, and R?ssler system. It offers a general way of choice for the controller, and furthermore, for some concrete systems the controller can be simplified. Numerical simulation results are presented to demonstrate the effectiveness of the proposed method.
2006, 55 (11): 5688-5693.
doi: 10.7498/aps.55.5688
Abstract +
In this paper, a new one-way Hash function is proposed based on chaotic neural network. With the neural network with piecewise linear chaotic map as the output function, the key generation function based on spatiotemporal chaotic system are used to realized the data confusion and diffusion. By the cipher block chaining mode, the proposed method can produce 128-bit Hash value for plaintext with arbitrary length. Theoretical analysis and experimental results indicate that the proposed Hash function satisfies the demands in performance, such as being one-way, having initial value and key sensitivity, collision resistance and real-time applicability.
2006, 55 (11): 5694-5699.
doi: 10.7498/aps.55.5694
Abstract +
In this paper, the problem of finite-time synchronization is proposed. Terminal slide mode control is combined with chaos synchronization. Chaos synchronization is regarded as tracking problem in control system. Sufficient condition for constructing Terminal slide mode by introducing nonlinear function into linear slide mode function is given. Corresponding the Terminal slide mode controller is given too. To verify the feasibility and effectivness of this control strategy, the synchronization for Duffing chaotic system is illustrated.
2006, 55 (11): 5700-5706.
doi: 10.7498/aps.55.5700
Abstract +
An algorithm for one-way Hash function construction based on tangent-delay ellipse reflecting cavity-map system (TD-ERCS) is proposed in this paper. In the algorithm, the plaintext dealt with is first transformed into a systemic parameter sequence linearly, and then TD-ERCS is iterated in order of the parameter sequence directly, the final Hash value of 160 bits is obtained by means of the nonlinear transform on the iteration sequence, and no padding of calculation is added. Users’ keys of the algorithm can be chosen in the region［264, 2160］ arbitrarily. Theoretical analysis and basic security tests indicate that our Hash function has good one-way, weak collision property, better security than other chaotic Hash functions, and it can be realized easily with great rapidity. Our algorithm of Hash function is an ideal substitution for conventional Hash function. And also, a natural criterion (theoretical value of 85.33) to evaluate collision property of Hash function is educed in this paper.
2006, 55 (11): 5707-5713.
doi: 10.7498/aps.55.5707
Abstract +
This paper proposes a novel circuit design and implementation approach of generating multi-scroll chaotic attractors from high-order Jerk systems. According to high-order Jerk equations, multi-scroll high-order general Jerk circuits are designed by constructing a sequence of step functions with parameter control. The prominent feature for this kind of circuit design method is self-unified and in a sense universal. Based on the uniform circuit, both forth-order and fifth-order general Jerk circuits can be realized with the switching control. The switch set is also used to control the number of scrolls. Finally, the computer simulations and hardware implementations are given to generate multi-scroll chaotic attractors on the forth-order and fifth-order general Jerk circuits.
2006, 55 (11): 5714-5720.
doi: 10.7498/aps.55.5714
Abstract +
Facing to the ferroresonance over voltage of neutral grounded power system, an improved learning algorithm based on RBF neural networks is used to control the chaos system. The algorithm optimizes the object function to derive learning rule of central vectors, and uses the clustering function of network hidden layers.It improves the regression and learning ability of neural networks. The academic derivation testifies the errors and precision could satisfy demand of chaos control.And simulation calculation also displayed that the rate of convergence of the improved RBF neural network is much quickly and approach ability is much stronger. The numerical experimentation of ferroresonance system testifies the reliability and stability of using the algorithm to control chaos in neutral grounded power system.
2006, 55 (11): 5721-5727.
doi: 10.7498/aps.55.5721
Abstract +
We investigate the exact quantum motions of two ions in a two-dimensional Paul trap. When the Coulomb-correlation of the system is considered, we obtain a set of exact solutions of the system and the corresponding perturbed solutions, containing the exact discrete eigenstates and eigenenergies, and the approximate piecewise continuous spectra and the band structure. Taking several quantum states with lower quantum numbers as examples, we compute the average distances between two ions and give the plots of probability distribution of the two ions.
2006, 55 (11): 5728-5732.
doi: 10.7498/aps.55.5728
Abstract +
Fundamental principles of high-frequency chaos generation and synchronization in Er-doped fiber ring lasers are analyzed. The experimental configuration for generating wavelength-tunable chaos is proposed, and high-frequency chaotic lasers at different wavelengths are generated. Synchronization between the chaos generated in the receiver laser and the chaos transmitted over 1 km that is generated in the transmitter laser are achieved, which paves the way for constructing the high speed secure chaos communication network.
2006, 55 (11): 5733-5739.
doi: 10.7498/aps.55.5733
Abstract +
The conditions of constraint are treated by means of the mean constraint plane and the mean jump equation, in which the method of the Chebyshev polynomial approximation, previously used to explore period-doubling bifurcation of stochastic smooth systems, is applied to stochastic non-smooth systems. Numerical simulations show that period-doubling bifurcation exists in stochastic Duffing one-sided constraint system just as in smooth stochastic Duffing system, and furthermore, the Chebyshev polynomial approximation is an effective method in exploring the dynamical behavior of stochastic non-smooth system.
2006, 55 (11): 5740-5744.
doi: 10.7498/aps.55.5740
Abstract +
Amorphous BCN was prepared by ball milling the mixture of graphite and hexagonal BN for 120h, and then annealed for 45 min. at 1600K under 4.5GPa. The XRD，TEM and Raman scattering measurement indicated that the as-prepared sample consists of hexagonal phase Ⅰ with lattice constants a1=0.2551nm and c1=0.6716nm and hexagonal phase Ⅱ with lattice constants a2=1.2360nm and c2=0.8570nm, of which the hexagonal phase Ⅱ is an unknown phase of boron carbon nitride. Three characteristic Raman peaks located at 1279, 1368 and 1398cm-1 respectively, were observed in the Raman spectra recorded at room temperature. The temperature dependent Raman scattering spectra of the sample were taken at temperature ranging from 93 to 673K.The measuring results indicate that the hexagonal phase of Ⅰ mainly exist in the sample at 93K and hexagonal phase of Ⅰ convert to hexagonal phase of Ⅱ completely when at above 473K.The phase transition from the hexagonal phase of Ⅰ to Ⅱ occurs with increasing temperature, vice versa. The mechanism of the phase transition is discussed in the present work.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2006, 55 (11): 5745-5754.
doi: 10.7498/aps.55.5745
Abstract +
The calculation of Dirac operator determinant in non-Abelian gauge theory is generalized from only containing hard fermion mass to that containing momentum dependent fermion self energy, and the calculation of determiant and fermion condensate is generalized to the case with arbitrary external gauge fields.
2006, 55 (11): 5755-5759.
doi: 10.7498/aps.55.5755
Abstract +
Complex astigmatic elliptical beams possess very high orbital angular momentum. This kind of beams has important applications in many fields, such as atomic physics and biology. An experimental method of optical torsion balance to measure the orbital angular momentum of the beams is presented in this paper. In our experiment, the absorption slice rotates under the irradiation of the beam. The angular momentum of beams is obtained by measuring the rotation angle of the absorption slice. The angular momentum of complex astigmatic elliptical beam with different parameters is measured in this paper. The dependences of orbital angular momentum on the parameters of the elliptical beams are investigated. The experimental results are consistent with the theoretical predictions.
2006, 55 (11): 5760-5763.
doi: 10.7498/aps.55.5760
Abstract +
In this paper we present an improved nuclear density model. We have found the nuclear effect parameters’ formula RAV(x,Q2) and RAS(x,Q2) for the valence quark distribution and sea quark distribution in the nucleus, in which we have used the relation between the nuclear density and the mean binding energy in nucleus. By using the model, we can well explain the experimental data of the of Drell-Yan process in P-A.
2006, 55 (11): 5764-5768.
doi: 10.7498/aps.55.5764
Abstract +
Using the carbon coated expanded polystyrene (EPS) beads as filling admixture, the electromagnetic (EM) wave absorber more moistureproof and environment adaptive than the conventional absorber used in anechoic chamber was fabricated. The effective permittivity of the mixture with carbon volume content 1% was calculated by the strong fluctuation theory combining with Maxwell-Wagner theory; and the EM wave absorbing property of a laminated model filled with carbon coated EPS beads was predicted through calculation. Comparison with the experiment indicated that the results of calculation accorded with the experiment closely, and can be used for the design of the moistureproof EM wave absorber.
NUCLEAR PHYSICS
2006, 55 (11): 5769-5773.
doi: 10.7498/aps.55.5769
Abstract +
Based on the isospin- and momentum-dependent transport model IBUU04, we investigated the neutron-proton differential flow in the 132Sn+124Sn mid-central collisions at beam energies of 400MeV/A, 600MeV/A and 800MeV/A by adopting two different symmetry energies. It was found that the neutron-proton differential flow as a function of rapidity is very sensitive to the density dependence of symmetry energy， especially at incident energies around 400MeV/A.
2006, 55 (11): 5774-5778.
doi: 10.7498/aps.55.5774
Abstract +
Some experiments at Institute of Applied Electronics of CAEP showed that the interaction between the virtual cathode oscillator and the cavity is a key factor in determining the output microwave power and propagating modes. Particularly, we observed that the E-beam plays an important role in the cavity formation. The experiments have been carried out with 350 kV diode voltage and 23 kA diode current, where pulsed microwaves of 500 MW in peak power and 3.3 GHz in frequency have been obtained. The energy conversion efficiency from the electron beam to microwave is about 6.2%, and the output microwave modes are mainly the TM01 mode and TE11 mode. The cavity resonance effect on a coaxial virtual cathode oscillator has been investigated in detail.
2006, 55 (11): 5779-5783.
doi: 10.7498/aps.55.5779
Abstract +
Photon statistical properties of coherent field and thermal field are experimentally studied by means of direct photon counting using only one single-photon-counting module (SPCM) operating in Geiger mode. The second-order degree of coherence as affected by photon counting rate and selected resolution time is investigated systematically. By taking into account all the experimental factors which can influence the g(2), the second-order degree of coherence of an unknown optical field can be determined quickly and simply via single SPCM when choosing proper detecting conditions. In our experiment, when the counting rate is about 109 kc/s and the resolution time varies from 28 ns to 212 ns, the measured results can reliably reflect the different second-order degree of coherence of coherent and thermal fields.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (11): 5784-5789.
doi: 10.7498/aps.55.5784
Abstract +
In this paper, We first fitted the numerical results of the ionization potential calculated by Thomas-Fermi statistical model and gained the analytical function of the potential versus the degree of ionization, then calculated the ionization potential and the average degree of ionization for argon versus temperature and density in local thermal equilibrium (LTE) case. The curve of pressure versus specific volume V of argon plasmas is calculated according this simplified model. The calculated results by this simplified model are in agreement with experimental data and the calculated results of the Saha-equation theory. This simplified model can be used to the calculation of the equation of state of plasmas mixture and is expected to be widely used in the field of EML technology involving the strongly ionized plasmas.
2006, 55 (11): 5790-5794.
doi: 10.7498/aps.55.5790
Abstract +
A double band left-handed (LH) microstrip is designed based on defected ground structure (DGS) and Split Ring Resonators (SRRs) with broad bandwidth and low loss while the size of the unit cell is small and the synthesis is simple. Its effective permittivity and permeability are both extracted from the transmission and reflection data of the left-Handed microstrip, then the wave number k is calculated, and the results demonstrate that the LH microstrip shows backward wave (BW) properties in the broad frequency range of interest.
2006, 55 (11): 5795-5802.
doi: 10.7498/aps.55.5795
Abstract +
In this paper, we propose a novel scheme to produce a longitudinal controllable double-well optical dipole trap for cold atoms (or cold molecules), which is composed of a binary π-phase plate and a lens. The π-phase plate consists of two homocentric rings with equal area and opposite phase (0 and π), and its central region is opaque. When a plane light wave passes through the above optical system, a double-well optical trap will be formed at two sides of the focal point along the optical axis. The outer radius of the binary π-phase plate can be controlled by adjusting the radius of a diaphragm, so that a double-well optical trap will evolve and finally combined into a single-well, or vice versa. We briefly introduce the basic principle and derive several optimal parameters of the trap, and show the dependence of the optical parameters (including intensity distributions) on the geometrical parameters of the system. Our study shows that the proposed controllable optical trap can be used not only to trap cold atoms (or cold molecules) and realize all-optical, double-well or two species Bose-Einstein condensation (BEC), but also to study the trapped-atom (-molecule) interference, or form a 2D array of double-layer optical traps for cold atoms (or molecules), even to prepare a novel 2D optical lattice, and so on.
2006, 55 (11): 5803-5809.
doi: 10.7498/aps.55.5803
Abstract +
We have calculated electron energy loss spectrum for electrons transmitted through a mask in projection electron lithography by Monte Carlo simulation based on the dielectric function model and Mott elastic scattering cross section. A good agreement between simulation and experiment is obtained. The calculation results of the transmission and contrast for the masks in scattering angular limitation for projection electron lithography show that the contrast is dominated by the thickness of scattering layer (thicker the scattering layer higher the contrast), but is less affected by the thickness of the supporting membrane. Furthermore, with the increasing aperture angle the transmission increases but the contrast reduces, and the contrast decreases with increasing primary energy of electrons.
2006, 55 (11): 5810-5814.
doi: 10.7498/aps.55.5810
Abstract +
The products of fast ions H+, H+2 and H+3 with the energy of 0.6 to 1.8MeV passing through carbon films were measured. The yields of neutral atom H and negative ion H- for H+ at energies of 0.6,0.9,1.2,1.6 and 1.8MeV were obtained, respectively. The fitted yield curves as function of velocity of projectile agreed with experimental results very well. The transmission of H+2, H+3 at energies 1.2MeV and 1.8MeV through carbon film were also measured. The fitted transmission curves as function of dwell time of H+2, H+3 in carbon film were also obtained. Theoretical analysis and discussion on the electron loss and capture possibility in solids were made.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (11): 5815-5823.
doi: 10.7498/aps.55.5815
Abstract +
Based on the equivalence principle and the reciprocity theorem, the problem of electromagnetic scattering from two adjacent objects is considered and a solution that accounts for multiple scattering up to second-order is evaluated. In general, the first-order solution can easily be obtained by calculating the scatted field from isolated targets when illuminated by a plane-wave. However, due to the difficulty in formulating the coupled scattering field, it is impossible to find an exact analytical solution for the second-order scattered field. In this work, the second-order solution of electromagnetic scattering from two adjacent conducting/dielectric objects is derived by employing the reciprocity theorem and this solution is simplified from volume integral to surface integral form by using the equivalence principle. Meanwhile, the relation between the secondary scattering field from one target and the other is derived. Finally, the composite scattering field from two adjacent spheres is calculated using the formulas obtained in this work. The bistatic scattering pattern is discussed and the results are compared with numerical computations based on Time Domain Integral Equation Method (TDIEM).
2006, 55 (11): 5824-5828.
doi: 10.7498/aps.55.5824
Abstract +
A scheme employing a lens array and the technique of smoothing by spectral dispersion is presented for uniform irradiation on targets in inertial confinement fusion. Quasi-near field spots with a profile of sharp edge and flat top can be obtained with a diffraction-weakened lens array, while the speckles imposed on the spot by beamlets interference can be smoothed by spectral dispersion. Simulation results indicate that this scheme is a good candidate for improving the irradiation uniformity. The dependence of the smoothing performance on the characteristics of phase modulation and dispersion is further discussed, and it is found that parameters of the system of spectral dispersion and lens array must be chosen carefully to make optimal compromise between uniformity and usable energy of the laser beam.
2006, 55 (11): 5829-5834.
doi: 10.7498/aps.55.5829
Abstract +
A method to determine the growth polarity of GaN/AlGaN multi-quantum wells (MQWs) has been proposed. Electron holography (EH) study of the potential profiles of the multi-quantum well structure has been used here to determine the direction of build-in electric field that is strictly related to the growth polarity.
2006, 55 (11): 5835-5841.
doi: 10.7498/aps.55.5835
Abstract +
The interactions between a two-level atom and a coherent field with a time-varying frequency without rotating-wave approximation have been investigated. The typical cases of the frequency of the field varying with time in the sine and rectangle forms have been considered. It is found that the collapse-revival phenomena and quick oscillations due to virtual photon processes of the atomic population inversion are deformed as the frequency changes with time in the sine form. The rectangular frequency modulation can lead to some new collapses and revivals in the evolution of the atomic population inversion. The sudden jumping of the field frequency can also lead to the sudden change of the quick oscillations due to virtual photon processes.
2006, 55 (11): 5842-5847.
doi: 10.7498/aps.55.5842
Abstract +
The light power-current (L-I) characteristics of vertical cavity surface emitting lasers (VCSEL)，which have the same fabrication process and structure, but different detunings of Fabry-Perot (FP) resonance from the gain peaks at room temperature, were measured in the temperature range from 261K to 369K. The relationships between the output light power, threshold current, slope efficiency and lasing wavelength and the temperature were studied using the obtained characteristics in combination with the test results of their reflectivity spectra and photoluminescence signals, as well as the simulated results of their reflectivity spectra and gain spectra at different temperatures. The temperature characteristics of the new material AlInGaAs were found. The effect which the differences between the gain spectrum and the FP resonance had on the output characteristics, especially on the threshold current had been obtained. We found that VCSEL devices with minimal threshold currents and small threshold current change with temperature at room temperature could be obtained by adjusting the detuning of Fabry-Perot (FP) resonance from the gain peak. Using this method, AlInGaAs/AlGaAs strained quantum well VCSEL devices which have the characteristic temperature of 333K, and minimal threshold current and small threshold current change with temperature in the 321K to 345K range were fabricated.
2006, 55 (11): 5848-5854.
doi: 10.7498/aps.55.5848
Abstract +
An optimized comprehensively analytical thermal model was developed in accordance with interior heating characteristics of a gain-guided, top-emitting vertical-cavity surface-emitting laser with c.w. operation under room temperatures. Lateral thermal effects in AlInGaAs/AlGaAs vertical-cavity surface-emitting lasers were calculated analytically in detail. The comprehensively analytical solutions exhibited a clearer physical picture of the lateral heat-flux diffusion. The theoretical predicts of the interior thermal variation within the device were consistent with the experimental results as well. The work provides a useful tool for investigation of thermodynamic properties of the vertical-cavity surface-emitting lasers under thermal steady state, optimization of the device structure and control of the threshold current and power saturation effect, especially for the lateral thermal crosstalk in 2-dimensional arrays.
2006, 55 (11): 5855-5858.
doi: 10.7498/aps.55.5855
Abstract +
We have investigated the periodic poling characteristics of MgO: LiNbO3 and properties of the domain wall velocity. Based on back-switching reaction, domain-inverted velocity can be accurately controled by multi-impulse electric field, which can be used to fabricate MgO: LiNbO3 with submicron uniform periodical structure. At the same time, we studied the cause of formation and the mechanism of submicron domain-inverted structure.
2006, 55 (11): 5859-5865.
doi: 10.7498/aps.55.5859
Abstract +
The generation of group delay ripple and reflection sideband is explained by the oscillazation theory. And the effect of non-constant change of averaged index modulation induced by the one-side exposure apodization on the characteristics of chirped gratings is analyzed for the first time. The mechanism of apodization to enhance the performance of chirped fiber Bragg gratings is studied also. Based on the study, a simple apodization method to improve the performance of chirped fiber gratings is proposed, in which only one-sided exposure is needed which is easy to realize.
2006, 55 (11): 5866-5871.
doi: 10.7498/aps.55.5866
Abstract +
The multi-scattering theory (MST) method is applied to study the band structure of the two-dimensional phononic band-gap material. A comprehensive study is performed for the coupling between various order components of the cylindrical scattered wave. It has been found that there are decoupling effects at the edge of the band gap. Therefore, a self-contained self-consistent multiple scattering model of the zeroth-order scattered wave is obtained at the edge of the first band gap. A Mie scattering factor and a lattice structure factor are introduced to give a physical insight into the variation of the gap’s starting frequency by graphic analytic method.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (11): 5872-5877.
doi: 10.7498/aps.55.5872
Abstract +
The configuration and mechanism of a microhollow cathode discharge (MHCD) is introduced in this paper. The focus is a new type of cold atmospheric large-area plasma source, the fused hollow cathode (FHC) plasma source based on radio frequency hollow cathodes. Through its applications and related research, we present the characteristics of the hollow cathode discharge and the factors on which its characteristics depend, such as the cathode material, gas specy, frequency, gas flow, pressure, inner diameter of cathode, and the like. Two other types of related MHCD systems are given in addition.
2006, 55 (11): 5878-5884.
doi: 10.7498/aps.55.5878
Abstract +
Non-local transport characteristics of the deep sub-micrometer NMOS device are studied under electro-static discharge (ESD) stress. The result obtained shows that velocity overshoot may increase the drain current and has a great impact on the device characteristics, and that the energy relaxation time is correlated closely with the electric field of some point in the device as well as the velocity and the energy of the carriers, thus constant value is not appropriate for this parameter. The energy relaxation time and the high field mobility as functions of the carrier energy are gained by Monte Carlo calculation, and then device simulation is performed with these parameter models. Comparing ESD simulation with experimental results shows that accurate result about the I-V characteristics can be gained by using the models of the energy relaxation time and the high field mobility.
2006, 55 (11): 5885-5891.
doi: 10.7498/aps.55.5885
Abstract +
The interaction between laser and material can induce strong shock wave, so a new subject of science and manufacture technology—photomechanics is being founded on the basis of the mechanical effect of laser induced shock wave which is applied in areas such as laser shock shaping and laser spallation measurement. One of the key problems is to enhance the pressure peak value of shock wave effectively, for which the overlay is generally introduced in laser shock processing to improve the shock effect. So it has important theoretical significance and application value to study the influence of overlays exerting on the shock wave pressure. With respect to rigid overlays, flexible overlays and fluid overlays respectively, we analyze the influence from the aspects of the state of surface of discontinuity of laser induced shock wave, the diffusion of gasified material and plasma and the reflection of shock wave. It is found that overlays do not raise the pressure peak value directly when the pulse width is shorter than the time for the shock wave to cross the gasified material. On the contrary, shot of laser pulse with width longer than the time of shock wave crossing the gasified material heightens the shock effects by heightening the pressure by way of restricting the diffusion of gasified material and plasma and prolonging the acting time of useful pressure through multiple reflection of the shock wave betiseen the surfaces of the workpiece and the overlay. The rigid overlay can raise the pressure peak value of shock wave greatly. But the advantage of the flexible and fluid overlays is the adaptation to the form of the surface of non-planar workpieces.
2006, 55 (11): 5892-5898.
doi: 10.7498/aps.55.5892
Abstract +
By using a two laser beam method, the spectra of laser-induced air plasmas (LIAP) were studied experimentally. Two laser beams of a laser were used in the experiment. One of the beams was used to create the plasmas, which is called the ionizing-laser-beam (ILB), and the other beam was used to give influence to the plasmas, called action-laser-beam (ALB). This paper reports the experimental results and give a preliminary analysis of the modifications to the spectral characteristics due to the influence of the ALB. The experimental results indicated that the total spectral intensity of laser-induced air plasmas increased obviously under the action of the ALB. The increment of continuous spectra was greater than that of the line spectra; the increment of the short wavelength band was greater than that of the long wavelength band. The longer the delay-time of ALB behind the ILB, the larger the increase of spectra intensities. There is no threshold for the ALB to increase the laser-induced air plasmas spectral intensity. The results also showed that besides increasing the intensity, the decay-time for most of lines would increase under the influence of ALB. The preliminary analyses indicated that the results may be caused by electrons in the plasma which transfer their energy absorbed from the ALB via different routs with different efficiencies. These results provides some new sight into the microscopic mechanisms of the decay of laser-induced air plasmas, and also provides some experimental evidences for prolonging the decay-time of laser-induced air plasmas for some technical applications.
2006, 55 (11): 5899-5904.
doi: 10.7498/aps.55.5899
Abstract +
The effect of laser incidence angle on the angular distribution of hot electrons generated in the interaction of an ultrashort intense laser pulse with the foil target are investigated. A new emission peaked in the target surface direction is observed for the first time. With the increase of the incidence angle, the ratio of the number of surface electrons to the total electron number increases, while the number of transmitted electron through the target decreases. It is believed that the surface hot electrons are caused by the confinement of the quasi-static surface magnetic field and electric field.
2006, 55 (11): 5905-5908.
doi: 10.7498/aps.55.5905
Abstract +
Property of rectangular structure surface wave plasma was reported. Large-area uniform and high density plasma was produced by the optimization of slot antenna and the shape of dielectric plates. Plasma density and electron temperature for different operation conditions were measured by a Langmuir probe. Profile of plasma density along the vertical direction was modeled by a diffusive model, and the simulation result can be used to interpret qualitatively the measurement value very well.
2006, 55 (11): 5909-5916.
doi: 10.7498/aps.55.5909
Abstract +
Energy spectrum and angular distribution of fast electrons are measured in the interaction of linearly (P and S) and circularly polarized femtosecond laser pulses with an aluminum target. It is interesting to note that the angular distribution of backward going electrons is unique for S and circular polarization. For S polarization, the angular distribution of fast electrons can be explained by taking account of the surface magnetic field qualitatively.
2006, 55 (11): 5917-5922.
doi: 10.7498/aps.55.5917
Abstract +
Experimental study on plasma radiation characteristics of W wire array Z pinch with different initial parameters performed on Qiangguang-Ⅰ pulsed power generator of 1.4—2.1MA current with 80—100ns rise time is reported. The generator configuration and the diagnostic system for the experiments are briefly described. The total X-ray energy and peak power have been measured, and the maximum of X-ray energy and peak power are 34kJ and 1.28TW，respectively. In additional, the main results and conclusions are discussed also.
2006, 55 (11): 5923-5929.
doi: 10.7498/aps.55.5923
Abstract +
On the basis of one-dimensional fluid model, the characteristics of a homogeneous discharge at atmospheric pressure in nitrogen are numerically investigated. The primary processes of excitation and ionization in N2 are considered. The species included in the model are the electron e，N2 in the ground state，two ions N+2，N+4 and two metastable states N2(a1∑-u)，N2(A3∑+u). The simulation results show that the discharge in N2 appears mostly as a low-pressure Townsend discharge. The amplitude of discharge current is small and the gas voltage changes slowly in the breakdown phase. The electron density is much lower than that of ions and its maximum value occurs at the anode. Electrons are not trapped in the gas gap. There is no quasineutral plasma domain. The densities of metastable states N2(a1∑-u) and N2(A3∑+u) are at least three order higher than that of electron. The maximum metastable densities are located close to the anode, which determines the space structure of N2 discharge. Seed electrons needed in discharge are mainly provided by Penning ionizations between metastable molecules. This regime results in a low ionization level, which makes the discharge in N2 being close to a Townsend discharge. When changing discharge conditions properly, multiple-peak discharge can be obtained in N2.
2006, 55 (11): 5930-5934.
doi: 10.7498/aps.55.5930
Abstract +
We present a theoretical and computational model to study the ionization of the electron cyclotron resonance (ECR) microwave discharge using a quasi-three-dimensional electromagnetic particle-in-cell plus Monte Carlo collision method. The interaction between the charged particles and microwave fields are described by particle-in-cell method. The collision processes are treated with Monte Carlo method. Elastic, excitational, and ionizing electron-neutral collisions and elastic, charge exchange ion-neutral collisions are included. The cross sections are the functions of particle’s energy. The theoretical part of simulation is introduced in detaid as foundation of the numerical simulation.
2006, 55 (11): 5935-5941.
doi: 10.7498/aps.55.5935
Abstract +
We present a theoretical and computational model to study the ionization of the electron cyclotron resonance (ECR) microwave discharge using a quasi-three-dimensional electromagnetic particle-in-cell plus Monte Carlo collision method. The simulation code is original. The detailed information about the distribution of charged particles and electromagnetic fields are obtained. We can conclude that the electrons absorb energy from microwave near the ECR region. Many electrons and ions are created through the ionization collisions between electrons and neutrals. And the distribution of charged particles vary gradually from anisotropic to isotropic by the frequently collisions.
2006, 55 (11): 5942-5946.
doi: 10.7498/aps.55.5942
Abstract +
Framing shadowgraphy of UV laser probing with the 4th harmonic Nd-YAG Laser was developed for the diagnosis of Z-pinch plasmas. This system can effectively shield visible light and has advantages of high temporal resolution, large optical angular aperture and wide measuring range. The designed parameters and experimental results in implosions of tungsten wire array are presented in this paper.
2006, 55 (11): 5947-5952.
doi: 10.7498/aps.55.5947
Abstract +
Pinhole imaging of the neutron production in laser-driven inertial confinement fusion experiments can provide important information about performances of various capsules designs. In order to get good results in experiments, it is needed to judge the performance of various pinhole designs qualitatively or quantitatively before experiment. Calculation of imaging can be simply separated into pinhole imaging and image spectral analysis. In this paper, pinhole imaging is discussed, codes for neutron pinhole imaging and image showing is programed. The codes can be used to provide theoretical foundation for pinhole designing, either to provide simulating data for image analysing.
2006, 55 (11): 5953-5958.
doi: 10.7498/aps.55.5953
Abstract +
The problem that Cherenkov radiation may exist in the ion-channel when a relativistic electron beam (REB) is injected into plasma has been demonstrated and studied. The effect of the beam-wave interaction in ion background is analyzed by use of the linear perturbation theory. The dispersion equation and the simultaneous radiation condition of the system are derived. It is clearly shown that the electromagnetic instability of the system results from the coupling of the TM mode in ion-channel to the beam mode via the electron beam. Ion beam focusing is the microscopic mechanism. The ion-beam system in the moving plasma state is analyzed rigorously in theory. Then, the frequency shift of the radiation wave and the wave growth rate in ion-channel are presented. Finally, the effects of the parameters of the system on them are discussed by numerical calculation.
2006, 55 (11): 5959-5963.
doi: 10.7498/aps.55.5959
Abstract +
Low-temperature polycrystalline Si films were fabricated by radio frequency plasma-enhanced chemical vapor deposition using SiH4, Ar and H2 as source gas. It was found that the content of H2 in the mixture plays an important role for crystallization of Si films. High-quality low-temperature polycrystalline Si films were obtained under the optimal amount of H2 in the source gas.
2006, 55 (11): 5964-5968.
doi: 10.7498/aps.55.5964
Abstract +
The runaway breakdown model induced by fast electrons is promising in explaining the nanosecond-pulse breakdown. In this paper, runaway process and collision ionization of fast electrons are discussed. Based on the relations between the electron energy and effective retarding force, the evolution of injected electron energy as a function of distance away from the avalanche head was simulated. The higher applied electric filed strength is, the lower the runaway energy threshold is and the more fast electrons can runaway, and gas pressures affect the runaway process of fast electrons greatly. Moreover, the runaway breakdown process under the high-voltage nanosecond pulse is described qualitatively.
2006, 55 (11): 5969-5974.
doi: 10.7498/aps.55.5969
Abstract +
The process of coplanar dielectric barrier discharge (DBD) has been investigated experimentally and theoretically by using a segmented-electrode system. The local discharge current, light emission intensity and the developing velocity of plasma on the cathode were obtained. The results of the experiment and the two-dimension fluid modeling are compared. It was shown that there exists a non-uniform field in plasma region which causes the disagreement between the local discharge and the light emission during the discharge development in coplanar DBD. The secondary electron emission producod by photon bombardment on the dielectric surface should be taken into account in studying DBD.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (11): 5975-5979.
doi: 10.7498/aps.55.5975
Abstract +
Measurements were carried out under hydrostatic pressure up to 0.5GPa at room temperature, by using an ultrasonic pulse-echo method to measure the transit time of longitudinal and transverse elastic waves (10MHz) in a Nd60Al10Fe20Co10 bulk metallic glass. Based on the experimental data, the sound velocity, density, elastic moduli and Debye temperature were derived as functions of pressure, and the Murnaghan’s equation of state was obtained. Moreover, the compression curve, the elastic constants and the Debye temperature of the bulk metallic glass are calculated on the basis of the similarity between their physical properties in the glass state and those in corresponding crystalline state. These results confirm that the elastic properties of Nd60Al10Fe20Co10 bulk metallic glass are related to its component elements.
2006, 55 (11): 5980-5986.
doi: 10.7498/aps.55.5980
Abstract +
Based on the theory of dislocations, we have constructed the four models of the 〈100〉{010}, 〈100〉{011}, 1/2〈111〉{011} and 1/2〈111〉{112} edge dislocations in bcc Fe using the molecular dynamics method, and the formation energy, core energy and core radius of the dislocations have been calculated respectively. The calculated results indicated that the formation energies of 〈100〉{010} and 〈100〉{011} edge dislocations are higher than those of 1/2〈111〉{011} and 1/2〈111〉{112} edge dislocations. This shows that the formation of 1/2〈111〉 edge dislocation is easier than that of 〈100〉 edge dislocation. However, the core radii of 〈100〉{010} and 〈100〉{011} edge dislocations are smaller than those of 1/2〈111〉{011} and 1/2〈111〉{112} edge dislocations. This shows that the atomic numbers locating at the singular region in the 1/2〈111〉 edge dislocation are greater than those in 〈100〉 edge dislocation. Therefore, the motion of 1/2〈111〉 edge dislocation is easier than that of 〈100〉 edge dislocation.
2006, 55 (11): 5987-5990.
doi: 10.7498/aps.55.5987
Abstract +
A V∶YAG single crystal was grown by the temperature gradient technique (TGT) with graphite heating elements, which exhibited two kinds of colorations of light-green and yellow-brown in different parts. Differences in absorption spectra of three samples with different colors suggest that the reduction effect of carbon diffused from the heating element should enhance the concentration of tetrahedral V3+ ions and induce the F color centers with absorption band peaking at 370nm. The three samples all exhibited light-green color after annealing under vacuum at 1300℃. From changes of their absorption spectra, it can be inferred that tetrahedral V3+ ions should be produced through the exchange of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under heat exciting. During the process of annealing, the F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states than +3 to further improve the concentration of tetrahedral V3+ ions.
2006, 55 (11): 5991-5995.
doi: 10.7498/aps.55.5991
Abstract +
The water saturated Arabidopsis seeds were irradiated with protons in air. The ion energy is from 1.1MeV to 6.5MeV. According to TRIM simulation, the damaged region of the seed induced by the incident ions is near the surface region of the embryo, half of the embryo and the whole embryo, respectively. The protons with high energy can damage the shoot apical meristem(SAM) in the embryo while the protons with low energy cannot. The ion fluence used in this experiment was in the range of 4×109 to 1×1014ions/cm2. The experimental results showed that both the germination and survival rates decrease while increasing ion fluence, and the fluence-response curve for different damaged region of the embryo has different characters. Besides SAM, which is generally considered as the main radiobiological target, the existence of a secondary target besides SAM is proposed in this paper.
2006, 55 (11): 5996-6000.
doi: 10.7498/aps.55.5996
Abstract +
The investigation of GdBaCo2O5+δ system using low frequency internal friction method indicates that there exists a relaxation internal friction peak originated from the jump of excess oxygen atoms. The excess oxygen content δ affects greatly the height, shape and position of the peaks, which reflects the state of the excess oxygen varying with the value of δ. When the excess oxygen content is very small, say for the sample with δ=0.005, the corresponding internal friction peak disappears. On increasing the excess oxygen the relaxation internal friction peak will be observed. Three different states of excess oxygen can be concluded from the relaxation peaks which exist in the samples with δ=0.278,0.407,0.421,0.431 and 0.515. In addition, an internal friction peak with the features of phase transition are also observed in samples with δ=0.421 and 0.515 at about 360K, which may be attributed to metal-insulator transition.
2006, 55 (11): 6001-6007.
doi: 10.7498/aps.55.6001
Abstract +
We have performed total energy calculations on the structural and adsorption properties of Cu(100) c(2×2)-N surface by using DFT PAW method. It is concluded that nitrogen adsorbed on a four-fold coordinated site with a perpendicular distance of 0.2? from the surface Cu layer. The shortest Cu-N bond length is calculated to be 1.83?. Geometry optimization calculation excludes the possibilities of adsorbate induced reconstruction mode suggested by Driver and Woodruff and the atop model. The simulated work function for this absorbate-substrate system is 4.65 eV which is quite close to that on the clean Cu(100) surface. The total energy calculations showed that the average adsorption energy per nitrogen atom in the case of Cu(100) c(2×2)-N is about 4.92 eV with respect to a solitude N atom. The absorption of nitrogen on the Cu(100) surface yields the hybridization between surface Cu and N atoms, and generates the localized surface states at -1.0 eV relative to Fermi energy EF. The present study provides a strong criterion to account for the argument on the scanning tunneling microscopy(STM) images from different research groups.
2006, 55 (11): 6008-6012.
doi: 10.7498/aps.55.6008
Abstract +
Stresses and its variation of coating and matrix are measured by XRD (X-ray diffraction). A test system that measures coating stress on the bonding interface is established, and the measurement of interface bonding status is researched. By using interfacial stress variation before and after coating debonding from matrix, combined with the physical parameters of coating material and temperatures field parameter of coating-matrix system, the bonding strength of coating-matrix is represented by the diffraction peak of coating residual stress. A new experiment method to measure bonding strength of coating and matrix is introduced which is applicable to measuring interfacial bonding strength of all kinds of polycrystalline thermal barrier coatings.
2006, 55 (11): 6013-6019.
doi: 10.7498/aps.55.6013
Abstract +
Two series of ZrN/AlON nanomultilayers were synthesized by reactively sputtering zirconium and aluminum oxide targets in the gaseous mixture of argon and nitrogen. The thickness of ZrN layers was fixed in one of the series and the thickness of AlON layers in the other. The composition, microstructure and mechanical properties of films were characterized by X-ray energy dispersive spectroscopy, X-ray diffraction, high resolution transmission electron microscopy and nanoindentation. The investigation results indicate that during the process of Al2O3 target sputtering in the mixed atmosphere, part of oxygen atoms in Al2O3 were replaced by nitrogen atoms, leading to the formation of aluminum oxynitride, AlON. Under the influence of the “template effects” of ZrN layers, the AlON layers that used to exist as amorphous under sputtering conditions were forced to crystallize and grew epitaxially with the ZrN layers when the thickness of AlON was limited to less than 0.9 nm. Correspondingly, the hardness of multilayers was remarkably enhanced to its maximum value of 33.0GPa. A further increase in the thickness of AlON layers led to the crystalline AlON layers transforming into amorphous. The epitaxial growth of multilayers was blocked, accompanied by the decline of hardness.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (11): 6020-6024.
doi: 10.7498/aps.55.6020
Abstract +
Intensity parametrization of the electric dipole transitions within 4f2 configuration of Pr3+ in SrAl12O19 are reported, in which the mixing of the 4f2 transitional states with the explicit 4f5d states is taken into account. A new set of phenomenological intensity parameters, Tkq, are put forward, which are obtained from a best fit of the calculated and measured relative intensities of transitions from the 3P0 level to the lower J multiplets. The fitted values, T33=3.26×10-5 and T53=-5.46×10-5, have been used to analyze the transitions originating from the 1S0 level. The present results are compared with that of the Judd-Ofelt analysis and the experimental measurements.
2006, 55 (11): 6025-6031.
doi: 10.7498/aps.55.6025
Abstract +
We present a first-principles study of the atomic hydrogen adsorption onto the Be(1010) thin film.There are two types of Be(1010)surfaces according to the interlayer spacing between the surface and its nearest-neighbor layer. We show that the H adsorption features on these two kinds of surfaces are remarkably different. The work function, averaged electrostatic potential, and the local charge density consistently show that the charge is transferred from H to Be for L-type surfaces, while the transfer process is inverted for S-type surfaces.
2006, 55 (11): 6032-6035.
doi: 10.7498/aps.55.6032
Abstract +
The potential energy curves of B2 and B19′ phase for NiTi alloys were investigated with the norm-conserving and plane-wave ultrasoft pseudopotential in the local density approximation. Our results reveals that the B19′ phase is more stable than the B2 phase at absolute zero temperature due to lower potential energy of the former. In the B2 phase, the alloying atoms Au and Fe (at Ni site) occupy the equilibrium positions, whereas Ti, Zr and Al (at Ti site) and Ni atoms are displaced from their equilibrium positions. In the B19′ phase, all the above atoms are exactly located at the equilibrium positions. The martensitic transformation may mostly be ascribed to the non-global minimum positions that the Ni and Ti atoms occupy.
2006, 55 (11): 6036-6041.
doi: 10.7498/aps.55.6036
Abstract +
Based on the density functional theory (DFT), using full-potential linearized augmented plane wave and improved local orbital (APW+lo) method, the structure and magnetism of the rare-earth permanent magnetic materials YFe11Ti are analyzed and calculated. The formation energy of YFe12，Y2Fe17 and YFe11Ti are calculated, The stabilization effect and the possible positions of the substituted atom Ti are discussed. The magnetic moments for the system and respective atoms are obtained. The calculated result is consistent with the experiment. The contributions of the density of states of the electrons to the magnetism are discussed.
2006, 55 (11): 6042-6046.
doi: 10.7498/aps.55.6042
Abstract +
The adsorption properties of metal atoms on the hydroxyl SiO2 surface have been studied by using first-principles calculation. It is found that In and Ga atoms are weekly bound to the surface, while Fe, Co and Ni atoms are bound to both Si and O atoms with strong chemical bonds. Potential energy surface and diffusion barrier calculations show that In (Ga) can easily diffuse on the surface because of a rather small diffusion barrier(0.1—0.3 eV). The obtained results are in close agreement with recent nano- synthesis experimental results.
2006, 55 (11): 6047-6054.
doi: 10.7498/aps.55.6047
Abstract +
The complete diagonalized Hamiitonian matrixes of 3d2/3d8 ion configuration with trigonal symmetry have been established by irreducible representation method. The spectral hyper-fine structure and the constants of crystal structure and zero-field splitting parameters of CsNiCl3 crystal, as well as the Jahn-Teller effect and the influence of the spin singlet on the ground levels of Ni2+ ion have been studied. The results agree with the experimental facts. Besides, taking into account the influence of the spin-spin (SS) coupling interactions and the Trees correction which were neglected in previous publications, we find that the zero-field splitting parameters arise from four mechanisms, namely: (1) Spin-orbit coupling mechanism; (2) Spin-spin coupling mechanism; (3) Spin-orbit and spin-spin combined coupling mechanism; (4) Spin-orbit and Trees correction combined coupling mechanism. The spin-orbit coupling mechanism is the most important one and the other three mechanisms can not be neglected.
2006, 55 (11): 6055-6060.
doi: 10.7498/aps.55.6055
Abstract +
The completely diagonalized Hamiltonian matrixes of order 120 of 3d3/3d7 ions configuration in the trigonal symmetry have been established by irreducible representation method and group theory, taking into account spin-orbit interaction and spin-spin interaction. The ground-state energy levels, the zero-splitting parameter and Jahn-Teller effect of ruby crystal were calculated with the matrixes. The contributions of spin doublets for the ground-state energy levels were studied. The results show that the contributions of doublets cannot be neglected. The values of theoretical calculation conform with the experiments. On this basis, the influence of spin-spin interaction on the fine structure and zero-field splitting parameter of ruby crystal was further studied, and we found that the influence of spin-spin interaction on the zero-field splitting cannot be neglected.
2006, 55 (11): 6061-6067.
doi: 10.7498/aps.55.6061
Abstract +
In order to further study the influence of the arrangement and matrix number of the conductive nanowires array on the field emission from the array, the more practical conductive hexagonal and square nanowire arrays were simulated with the mirror image floating sphere model in this paper. From the calculation results, the field enhancement factor of conductive nanowire array was expressed as the following expression:β=h/ρ(1/1+W)+1/2(1/1+W)2+3, in which h is the height of conductive nanowire, ρ is the radius and W is a function of the independent variable R, R is the interwire distance. All calculated results indicated that the arrangement of conductive nanowires array has less influence on the field emission, while the interwire distance critically affects the field emission. As RR0, the field enhancement factor decreases rapidly with R. When R>R0, the enhancement factor hardly changes, where R0 is the optimized interwire distance. The performance of field emission from conductive nanowire array hardly changes with the matrix number of the array, which only influences on the gradient curve of the enhancement factor. R0 would decrease to some extent with the increasing of the matrix number.
2006, 55 (11): 6068-6072.
doi: 10.7498/aps.55.6068
Abstract +
Electric pulse of photoconductive switches is determined by transmission character of photo-generated carriers. In the course of transmission, inductive current on the electrodes is formed by photo-generated carriers with high drift speed. Conductive current is formed only after the carriers are absorbed by electrodes. Inductive current and conductive current are calculated by numerical method in this paper. The result shows that inductive current cannot play a main part in the photoconductive switches’ output pulse unless under abnormal test conditions. And explaination of ultra-fast rise time of out put pulse faster than the time of carriers to pass between two electrodes with saturated drift speed is given.
EDITOR'S SUGGESTION
2006, 55 (11): 6073-6079.
doi: 10.7498/aps.55.6073
Abstract +
First-principle calculations in the frame of density-functional theory (DFT) in the general gradient approximation (GGA) are performed by using the augmented plane wave plus local orbital (APW+lo) method for pure GaAs(110) surface and the adsorptions of Xe atoms on it. A supercell consisting of five atomic layers is constructed to simulate the geometical configuration of clean GaAs(110) surface and the adsorption of Xe atoms. The Newton dynamics method is used to relax the atomic positions. Initiating with the Xe atom on top of Ga atom, As atom, and at the bridge site, respectively, it is found that the total energy of the supercell reaches the minimum when the Xe atoms are located at the bridge site. Additionally, it is shown that the adsorption of Xe atoms make the relaxed GaAs(110) surface to return to the ideal crystal geometrical configuration as generally expected.
2006, 55 (11): 6080-6084.
doi: 10.7498/aps.55.6080
Abstract +
Doubly stacked layers of amorphous silicon (a-Si) between amorphous silicon nitride (a-SiNx) layers have been fabricated by plasma enhanced chemical vapor deposition (PECVD)technique. Si nanocrystal (nc-Si) layers were formed by thermal crystallization of a-Si layers after a furnace annealing at 1100℃ for 30 min in N2 ambient. The phenomena of charge trapping and storage in nc-Si layers were observed in both capacitance-voltage (C-V) and current-voltage (I-V) measurements at room temperature. The structure has revealed a double-level charging process. Two stages of charge storage were evident in the series of C-V curves. The phenomena and mechanism of charge storage were discussed in detail.
2006, 55 (11): 6085-6089.
doi: 10.7498/aps.55.6085
Abstract +
After pre-metallization processing of AlGaN/GaN heterostructure with O2 plasma and HF solution, the Ni/Au Schottky contact characteristics were improved obviously and reverse leakage current reduced by three orders. In addition, annealing experiments were carried out at 200—600℃ for 5min in N2 atmosphere on many batches of Schottky diodes, the reverse leakage current decreased further with annealing temperature increasing. Especially after annealing at 600℃ for 5min in N2 atmosphere, the better uniformity of C-V characteristics at different frequencies indicated that surface trap density was reduced when Ni diffused to AlGaN/GaN surface during annealing. On the other hand, the C-V curves moved to the right and the reduction of absolute value of 2D electron gas depletion voltage proved that the Schottky barrier height was elevated when the annealing temperature increased.
2006, 55 (11): 6090-6094.
doi: 10.7498/aps.55.6090
Abstract +
In this work, a method for calculating mobility of nano-scaled MOSFETs from the Boltzmann transport equation(BTE) is presented. Some approximations are assumed for the BTE in nano-scaled MOSFETs, and an improved distribution function of the carriers is obtained which is used to model the mobility of carriers. An analytical expression of carrier mobility is deduced considering the statistical distribution of carrier velocity and carrier life-span and taking into account especially the interaction between the longitudinal and the transverse fields. The reasonable agreement of the calculated results with simulation validated the new model, which is explicit, simple and physically well grounded.
2006, 55 (11): 6095-6100.
doi: 10.7498/aps.55.6095
Abstract +
Nonv-electrical plating was employed to form nickel inducing source on the surface of α-Si thin film deposited by VHF-PECVD. It was observed that the nickel inducing source formed by this method appeared as “dots” uniformly distributed on the surface of a-Si thin film after annealed for several hours at 550℃. The quantity of “dot” on the a-Si was determined by Ni concentration in the solution, the PH value, and the plating times, etc. The lateral crystallization was observed if the density of “dots” is relatively low. Poly-Si with maximum grain size of 90μm was obtained from the original α-Si deposited by VHF-PECVD. High performance thin film transistor (TFT) monitors were fabricated using this poly-Si.
2006, 55 (11): 6101-6107.
doi: 10.7498/aps.55.6101
Abstract +
Porous silicon (PS) with different porosity was obtained by anode electrochemical etching of boron-doped Si (100); the as-etched samples were then covered with Fe films by magnetron sputter technique. Analysis of surface profile and structural investigation were done by scanning tunneling microscopy and X-ray diffraction. Magneto-optical Kerr effect was employed to measure the hysteresis loops of the iron films sputtered onto PS and the reference sample on the Si substrate. The coercivity of the PS-based Fe films is larger than that of the Si-based ones, and increases with the porosity of the PS substrate. As for the PS-based samples with the same porosity, the coercivity of Fe films decreases with their thicknesses in a certain range. We found that the spongelike structure of PS can be effectively used to control the coercivity of iron films on the PS substrates.
2006, 55 (11): 6108-6112.
doi: 10.7498/aps.55.6108
Abstract +
Magnetic properties and giant magneto-impedance (GMI) effects of FeCuCrVSiB single layered and multilayered films with Ag as the central layer and SiO2 as the isolating layers, which were prepared by radio frequency sputtering without field and with a magnetic field about 72kA/m along the films length, are investigated. The hysteresis loops of single layered films show that the samples deposited with a magnetic field possess excellent soft magnetic properties and the coercive force is only about 64A/m. After annealing at an optimum temperature of 230℃ for 1.5h, the maximum GMI ratios of single layered films are 37.5% in transverse field at the frequency of 13MHz, and the maximum GMI ratios of multilayered films is 277% at the frequency of 8.6MHz. The frequency dependence of the magneto-impedance indicates that the GMI effect in multilayered films can be very large even at relatively low frequencies.
2006, 55 (11): 6113-6117.
doi: 10.7498/aps.55.6113
Abstract +
The investigations on the structure, magnetic and transport properties were carried out for the double perovskite Sr2Fe1-xCoxMoO6 samples prepared by the solid state reaction method. It is found that the relationship between resistivity and temperature changes from a typical half-metal behavior to a semiconductor behavior, with the increasing substitution concentration x value of Co for Fe. The resistivity at room temperature increases from 3.9×10-5Ω·cm (for the x=0 sample) to 6.0×10-1Ω·cm (for the x=1.0 sample). The magnetic order in the sample changes from a ferrimagnetic to an antiferromagnetic and the magnetic transition temperature TN decreases with the increasing Co content x. The magnetoresistance effect is depressed by the Co partial substitution for Fe. The origin of magnetoresistance and the Co substitution effect were discussed in detail based on the analysis of electronic structure of Sr2Fe1-xCoxMoO6 system.
2006, 55 (11): 6118-6122.
doi: 10.7498/aps.55.6118
Abstract +
The characteristics of the TDDB (Time-dependent dielectric breakdown) under the CVS (constant voltage stress) and the gate current model of devices under V-ramp stress were studied in the 1.4nm-thick n-MOSFET. The degradation and failure mechanisms were analyzed. The gate current is produced by the tunneling, the electron surmounting and percolation. During the stress process, the created traps in the oxide not only debase the height of the SiO2 barrier, but also diminish the breadth of the barrier. Every trap engenders a conduction path. These paths enhance the gate current, degrade the device performance and prolong the broken-time of the gate oxide.
2006, 55 (11): 6123-6128.
doi: 10.7498/aps.55.6123
Abstract +
Lanthanum doped lead titanate (PLT) ferroelectric thin films were grown on Pt/Ti/SiO2/Si(100) substrates using RF magnetron sputtering. X-ray Diffraction (XRD) was applied to study crystalline properties of PLT films, and XRD patterns of PLT thin films show that there appeared (111) preferred-oriented tetragonal perovskite phase. The ferroelectric domain patterns and the corresponding topography of PLT thin films have been investigated using piezoresponse force microscopy (PFM) and atomic force microscopy (AFM), respectively. PFM observations show that there exist nanoscale banded 90° domain patterns 20 to 60 nm in width and low energy head-to-tail polarization configurations in PLT film. The relationship between fabricating conditions and properties of PLT10 thin films was studied. It was found that PLT10 thin film fabricated under the optimized conditions possess dielectric constant εr=365, dielectric loss tgδ=0.02, and pyroelectric coefficient γ=2.18×10-8C·(cm2·K)-1, respectively. The PLT thin films could meet the needs for uncooled pyroelectric infrared sensors.
2006, 55 (11): 6129-6135.
doi: 10.7498/aps.55.6129
Abstract +
Hot band of a continuous cast AA 2037 Al alloy was annealed at different temperatures ranging from room temperature to 500℃ for 3h. Vacancy-solute interaction and precipitates in the hot band samples during annealing were investigated by positron annihilation techniques, coincidence Doppler broadening (CDB) of positron annihilation radiation and positron lifetime spectroscopy, and other methods. The experimental results indicated that there existed V-Cu and V-Cu-Mg complexes at room temperature. At 200℃, positron mean lifetime shows a peak value because of the formation of semicoherent particles. The characteristic shape of Mn was observed in the CDB ratio curve, which indicated the formation of V-Mg-Mn complexes or the existence of Mn clusters in the semicoherent particles. Above 250℃, coarsening and dissolution of semicoherent particles resulted in the decrease of mean lifetime and disappearance of the Mn signal, but the Cu signal increased clearly with annealing temperature. After 350℃, the Cu signal tended to saturation, which reflected that the Cu dissolved might agglomerate and cluster with vacancies during cooling the sample to room temperature, while new increase of mean lifetime might be attributed to the formation of incoherent phase, which was verified by DSC curve.
2006, 55 (11): 6136-6140.
doi: 10.7498/aps.55.6136
Abstract +
Aligned and unaligned In2O3 nanowires were prepared based on our homemade equipment and the field-emission properties of In2O3 nanowires(NWs) were investigated.It was found that aligned In2O3 NWs have better performance than unaligned ones. The aligned NWs have lower turn-on and threshold electric fields. This might be attributed to the weaker field-screening effect between the neighboring aligned NWs, and the existence of more exposed tips as emitters in the aligned NWs.
2006, 55 (11): 6141-6146.
doi: 10.7498/aps.55.6141
Abstract +
The surface-conduction electron-emitter display(SED) based on tunneling effect is a newly developed flat panel display. It has obvious technical advantages and excellent characteristics and is praised as one of the most advanced displays. Based on the theory of electromagnetism, an equivalent physical model of a single pixel of SED is established. In particular, it shows the exterior charge densities in different parts of the pixel. Furthermore, the electric potential and electric field intensity are studied in detail, and their distribution is simulated with the help of MATLAB 6.5 Software. Finally, a theoretical analysis of the simulated curved surface is given, and the electrical behavior as well as the emission mechanism is explained comprehensively. In order to further interpret the behavior of electrons in SED, we compare this model with the multi-scattering model and the inertial centrifugal force model respectively. It is found that within the limits of error our conclusion on electric field distribution is consistent with that of the inertial centrifugal force model.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (11): 6147-6151.
doi: 10.7498/aps.55.6147
Abstract +
Hydrogenated microcrystalline silicon (μc-Si∶H) films with high crystalline volume fraction were deposited using a novel hot wire assisted microwave electron cyclotron resonance-chemical vapor deposition (HW-MWECR-CVD) system. The Raman scattering spectrum and X-ray diffraction measurements were carried out to characterize the microstructure of the films. It was shown that, in a wide range of silane dilution ratio, all the deposited films had high crystalline volume fractions. The transition phase from amorphous to microcrystalline silicon was more easily grown with higher silane dilution ratio, which was attributed to the higher ionization and decomposition of the source gases in HW-MWECR-CVD system than in other systems.
2006, 55 (11): 6152-6156.
doi: 10.7498/aps.55.6152
Abstract +
In oxyfluoride glass-ceramics, the fluoride nanocrystals doped with rare earth ions were dispersed in an oxide network. The emission of Eu3+ has high sensitivity to different crystal field and is suitable for microstructure research in neoceramic glass. Different oxyfluoride glass ceramics doped with Eu3+ were prepared. The variation of the emission spectra of Eu3+ in different glass ceramics confirms the applicability of Eu3+ ions in neoceramic glass as microprobe before and after heat treatment.
2006, 55 (11): 6157-6162.
doi: 10.7498/aps.55.6157
Abstract +
Isothermal oxidation behaviors of pure and yttrium-implanted nickel were studied at 900℃ in air. SEM and TEM were used to examine the oxide scales formed on nickel substrate. Acoustic emission (AE) technique was used to monitor the cracking and spalling of oxide film in isothermal oxidizing stage and subsequent air-cooling stage. AE signals were analyzed in time and number domain according to the related oxide fracture model. It was found that Y-implantation greatly lowered the isothermal oxidizing rate of nickel and improve the anti-cracking and anti-spalling properties of NiO oxide film. The main reason for the improvement was that Y-implantation greatly reduced the grain size of NiO and increased the high temperature plasticity and creeping ability of the oxide film. Meanwhile, Y-implantation reduced the size and number of Ni/NiO interfacial defects, hence remarkably enhanced the adhesion of protective NiO oxide scale formed on nickel substrate.
2006, 55 (11): 6163-6167.
doi: 10.7498/aps.55.6163
Abstract +
The synchrotron radiation (SR) stimulated etching of SiO2 thin film surface was investigated with a contact cobalt mask, and the etched pattern of SiO2 thin films on silicon was made. The SiO2 thin film was grown on silicon surface by thermal oxidation. The contact cobalt mask was fabricated on SiO2 thin film by combining the techniques of photolithography and RF-magnetron sputtering. In the experiment, the anisotropic etching of SiO2 was effectively achieved by SR radiation with SF6 as the reaction gas. The etching rate increased with increasing gas pressure of SF6 in a certain range, and with decreasing the substrate temperature. Under SR irradiation with flowing SF6 and O2 did not etch the silicon crystal and the etching stopped completely at the SiO2/Si interface. Furthermore, the Co provided high resistance against the SR etching, indicating that Co is an ideal mask material for the synchrotron radiation stimulated etching.
2006, 55 (11): 6168-6174.
doi: 10.7498/aps.55.6168
Abstract +
Colloidal crystals are fabricated through a self-assembly process of monodispersed polystyrene particles. Evolution of colloidal crystal structures is analyzed by Kossel diffraction technique and UV-Vis spectrophotometer. According to the changes in the Kossel patterns we find the crystal structures change with passage of time and experience successively the following stages: liquid state-random layer structure-stacking disorder structure-fcc with (111) twin-normal fcc structure. The plane distances of different crystal planes and the lattice constants are also determined in this study. The 111 plane distances and the lattice constants evaluated according to the measurement of transmission spectrum are in accordance with the results by the analysis of Kossel line. In addition, it was found that the peaks of the transmission spectrum become sharper and shift considerably toward shorter wavelength during the crystal evolution, showing the lattice constants become smaller.
2006, 55 (11): 6175-6184.
doi: 10.7498/aps.55.6175
Abstract +
A series of ZrO2 and polyvinylpyrrolidone (PVP) doped-ZrO2 sols have been synthesized by the controlled hydrolysis and condensation of zirconium n-propoxide, with diethanolamine (DEA) as the chelating agent. PVP-ZrO2 hybrid monolayers and highly reflective (HR) multilayer coatings were then prepared by spin-coating the stable sols on K9 glass substrates. The fabrication of the HR coatings involves alternate depositions of PVP-ZrO2 (as the high-index material) and SiO2 (as the low-index material) layers. The microstructures of the sols, the structural and optical properties, as well as the laser damage resistance of the films were thoroughly characterized. By virtue of the small angle X-ray scattering (SAXS) analysis, the sol-gel processing parameters were successfully optimized, endowing the as-prepared films with good optical properties and high laser damage resistance. SAXS studies also offer the possibility to a good knowledge of the microstructure of the sols. In our hybrid system, the unhydrolyzed DEA ligands, which become anchored in the inorganic network, may considerably weaken the effects of PVP on the formation and growth of ZrO2 particles. Hence, the incorporation of a proper amount of PVP gives rise to negligible change of the sol structure and only a slight variation in refractive index and laser damage resistance of the films. However, at the slight expense of the refractive index and laser damage resistance, the incorporation of PVP can easily alleviate the stress incompatibility between different layers and facilitate the fabrication of the multilayer coatings. As the mass fraction of PVP reaches 15%—20%, a perfect match between different layers can be achieved, which ensures the successful deposition of 21-layer, nearly full-reflection coatings with the minimum transmittance of about 1.6%—2.1% (at 1064nm) and high laser damage threshold of 16.4—18.2J/cm2 (at 1064nm, 1ns pulse duration and R/1 mode).
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (11): 6185-6191.
doi: 10.7498/aps.55.6185
Abstract +
The daily precipitation observational data of 740 stations from 1960a to 2000a Which provided by National Climate Center of Chinese Meteorologial Administration, are divided in sections and statistically analyzed. A common feature is revealed——the power-law distribution, and different precipitation corresponds to different power-law exponent; this to a certain extent reflects that different precipitation have different climate backgrounds and control systems. The power-law exponents of the seven climate regions of China show the trend of increase from southeast to northwest, this corresponds to the spatial characteristic of precipitation of China——more in east and less in west, more in south and less in north. The analysis on the characteristic of the temporal evolvement of the power-law exponent shows that the abruption points of the power-law exponent of northeast, east, and northwest of China correspond to the drying trend of northern China starting from 1970s.
2006, 55 (11): 6192-6196.
doi: 10.7498/aps.55.6192
Abstract +
Considering a non-feedback mechanism of action，the present paper shows that the steady forcing induces amplitude death in chaotic system by investigating the bifurcation figures and the spectrum of Lyapunov exponents of the R?ssler oscillator. The manner, which is very similar to that in coupled limit cycles or coupled R?ssler system, is from periodic to an equilibrium point of the forced system. Furthermore，we investigate the time series of the forced system, and find that when the strength of the forcing is beyond a critical constant，the states of the system present the periodic dynamics with a small amplitude or rest alternately.
