Vol. 52, No. 11 (2003)
The kinetics simulation of trap depths and capture cross sections of SETs in AgC l microcrystals doped with ［Fe(CN)6］4- complex
2003, 52 (11): 2649-2654. doi: 10.7498/aps.52.2649
To describe the photoelectron rise and decay process of AgCl microcrystals doped with ［Fe(CN)6］4-, a kinetics model composed of three in trinsic centres and a shallow electron traps(SETs)is set up, and further more, a set of differential equations is deduced. By solving the differential equations, photoelectron decay curve and photoelectron lifetime that is in accord with the transient microwave photoconductivity experimental data are obtained. Adjusting related simulation parameters, the SET depths and capture cross sections at room temperature for ［Fe(CN)6］4- are obtained and they are 0.115eV and 2 .136×10-17cm2, respectively.
2003, 52 (11): 2655-2659. doi: 10.7498/aps.52.2655
A new approach of color image segmentation based on the principle of MDM(maximum degree of membership)for fuzzy pattern recognition is reported in this paper. The colors of target and background obtained from the color histogram of the color image can be used to set some color fuzzy-sets, to which, based on the principle of MDM, the degrees of membership of colors of all pixels in the image in these fuzzy sets are calculated to determine their memberships. A MDM-radial basis function neural network is implemented to segment color images with higher speed and efficiency.
2003, 52 (11): 2660-2663. doi: 10.7498/aps.52.2660
In this paper,the Jacobi elliptic function method is generalized to study nonlinear evolution system. The envelope periodic solutions of long-short wave interaction equation are obtained. The solitary wave solutions for this model are also given under some conditions.
2003, 52 (11): 2664-2670. doi: 10.7498/aps.52.2664
In this paper, we have studied the positive problems of perturbation to the symmetries for relativistic Birkhoffian systems under the action of a small force of the disturbance. The fundamental theory, equations of motion and equation of small disturbance of relativistic Birkhoffian systems were established. Lie symmetries and conserved quantity of this systems were given. Perturbation to the symmetries of the systems under infinitesimal transformations, s-order adiabatic invariants, existence conditions and the form of adiabatic invariants were studied. We have also studied the inverse problems of perturbation to the symmetries for relativistic Birkhoffian systems. We obtain the perturbation to the symmetries of the systems under infinitesimal transformations, when the systems possess s-order adiabatic invariants. The relationship between relativistic Birkhoffian systems and classical Birkhoffian systems were studied. Finally an example was presented to illustrate the result.
2003, 52 (11): 2671-2677. doi: 10.7498/aps.52.2671
The propagation of solitons in an inhomogeneous dusty plasma composed of two kinds of dust grains with different masses is investigated by using the reductive perturbation technique. In the lowest order, if the interface of the two kinds of dust grains is discontinuous, the transmission and reflection waves can be both described by the KdV equation. The numbers and amplitudes of both transimtted and reflected solitons from an incident soliton are given analytically for this case. If the interface of the two kinds of dust grains is continuous, neglecting the reflection, the nonlinear dust acoustic wave can be described by a KdV-type equation in the lowest order. The amplitudes, propagating velocities of these quasi-solitons for this case are also given analytically in this paper.
Teleportation of a three-particle entangled W state through two-particle entangl ed quantum channels
2003, 52 (11): 2678-2682. doi: 10.7498/aps.52.2678
We propose a scheme for teleportation of a three-particle entangled W state through two-particle entangled quantum channels. Firstly, the maximally entangled states are taken as quantum channels, then, the case of nonmaximally entangled channels is considered. We find that when the channels are nonmaximally entangled states, by introducing an ancillary qubit and constructing an unitary transformation properly, teleportation of three-particle entangled W state can be implemented with certain probability.
A four-level system coupled with lasers is analyzed in terms of dressed-atom model by introducing auto-ionization decay which leads to a non-Hermitian Hamiltonian. The population of the system obtained by means of solving the secular equation of the Hamiltonian is found in good agreement with that from numerical solution of time-dependent Schrdinger equation. This result suggests that non-Hermitian Hamiltonian can be introduced into the framework of quantum mechanics , and the imaginary part of the corresponding eigenvalue represents the populati on decaying of systems.
2003, 52 (11): 2687-2693. doi: 10.7498/aps.52.2687
This paper studies the quantum entanglement of the Tavis-Cummings model for two steady identical two-level atoms interac-ting with a single-mode field. Whe n the field is vacuum and the two atoms stay in Einstein-Podolsky-Rosem entangle d state or disentangled state initially, we obtain that the system will evol ve to a three-body approximate W entangled state. The entanglement measure will change with the variation of system initial state, coupling coefficients, detuni ng degree and atomic population inversion. It should be noted that the atomic co upling coefficient exhibits the nonlinear effect and the entanglement measure os cillates periodically in accordance with atomic population inversion.
The solution of the Fokker-Planck equation of non-degenerate parametric amplific ation system for generation of squeezed light
2003, 52 (11): 2694-2699. doi: 10.7498/aps.52.2694
In this paper, we present the analytical solution of the Fokker-Planck equation of non-degenerate optical parametric amplification(NOPA)for generation of squeezed light. The maximum intra-cavity compression of squeezed light derived from the analytical solution is 1/16(vacuum fluctuations 1/4). To compare it with that of the previous result 1/8 of degenerate optical parametric amplification(DOPA), it seems that the squeezing for NOPA is superior to the squeezing for DOPA.
2003, 52 (11): 2700-2705. doi: 10.7498/aps.52.2700
The six-vertex model with open boundary conditions is discussed.The correlation functions for the model are calculated and expressed as some determinants.
Perturbation to the energy of Gaussian beam by a doubly polarized weak gravita tional plane wave in a static magnetic field
2003, 52 (11): 2706-2711. doi: 10.7498/aps.52.2706
First-order and second-order perturbations to the energy of Gaussian beam by a doubly polarized weak gravitational plane wave in static magnetic fields are discussed.The results of numerical estimation show that the perturbation to Gaussian beams by weak gravitational plane waves is very small,i.e.the total energy of the background fields would not change obviously in the influence of gravitational waves,but the perturbative power flux produced in the local region may be observable.
2003, 52 (11): 2712-2717. doi: 10.7498/aps.52.2712
The variational method is applied to a single-mode stochastic nonlinear optical system and the dependence of its relaxation rate and spectral amplification factor on the noise intensity based on the linear response theory is investigated.The investigation shows that when the biased input is vanishing,the relaxation rate has different dependence in monostable and multistable cases.The investigation also shows that the stochastic resonance occurs in one-dimensional symmetric monostable potential,and the possible condition for it is pointed out.
2003, 52 (11): 2718-2722. doi: 10.7498/aps.52.2718
Using the linear output feedback method, we investigate the resilient synchroniz ation for a class of chaotic systems. The influence of uncertainties in controll er itself is weakened. By the LMI (linear matrix inequality) toolbox, the resili ent controller is derived conveniently. Finally, the computer simulation results illustrate the validity of the method and the importance of the research.
2003, 52 (11): 2723-2728. doi: 10.7498/aps.52.2723
A novel genetic-based neural network control for chaos is presented. The method proposed has been successfully applied to control two simulated chaotic systems by incorporating the techniques of small perturbations and the periodic control in this paper. The simulation results showed that the neural network trained by genetic algorithm can learn to produce a series of small perturbations to conver t chaotic oscillations of a chaotic system into desired regular ones. The scheme requires no knowledge about the mathematical model. Moreover, the approach is r easonably robust to noise, it can be extended to control other chaotic systems.
2003, 52 (11): 2729-2736. doi: 10.7498/aps.52.2729
A class of piecewise smooth maps with three zones is derived to describe the dynamics of a current-programmed Buck-Boost converter operating in a discontinuous mode. The numerical simulation is carried out and the bifurcation diagrams w ith the input voltage as a parameter are obtained. It is shown that, when a bifu rcation occurs, some eigenvalues of the Jacobian matrix jumps over the unit circ le in a discontinuous way, and there are always some orbit points lying on the b oundaries which separate different regions in the phase plane. It is concluded t hat border collision bifurcations could occur when the input voltage varies, for example, a bifurcation from a periodic orbit to another periodic orbit or chaot ic orbit.
2003, 52 (11): 2737-2742. doi: 10.7498/aps.52.2737
How to design an efficient one-way Hash function is always the hot point in mode rn cryptography researches. In this paper, a Hash function construction method b ased on extended chaotic maps switch is proposed. The extended chaotic model is first built to generate various kinds of chaotic signals at different parts of t he original signals according to the switching schemes, and then chaotic paramet ers of one-way Hash function is modulated by the linear-transformed signals. The advantages of irreversibility, resistance to imitations and sensitivity to init ial values,etc., are also discussed. Simulation results show that this chaotic H ash function based on extended chaotic maps switch has good one-way，weak collis ion property, better security than the chaotic Hash function based on single cha otic map, and it can be realized easily.
The study of two-dimensional growth interface in Kuramoto-Sivashinsky and Karda- Parisi-Zhang models
2003, 52 (11): 2743-2749. doi: 10.7498/aps.52.2743
We have studied the evolution of (2+1)-dimensional surface morphology in the Kur amoto-Sivashinsky (K-S) and Karda-Parisi-Zhang (KPZ) models by using the numeric al simulation approach. The results show that the surface morphology has the sel f-affine fractal properties in both the models and exhibits a cellular structure after long-time growth in K-S model. With numerical correlation, dynamic scalin g characteristics are observed explicitly in both models, and the roughness expo nent, the growth exponent and the dynamic exponent are all obtained. From the si mulation results we suggest that the two models have the different properties in present time and space scale, and are not in the same universality class.
2003, 52 (11): 2750-2756. doi: 10.7498/aps.52.2750
In this paper, the car-following model with stochastically considering the relative velocity in a traffic flow is presented through investigating the vehicle a cceleration process with uncertainty. The stability criterion superior to the Ba ndo's model is derived by the linear stability analysis. The density wave is inv estigated analytically with the perturbation method. The results show that the o ccurrence of traffic jamming transitions can be described by the kink solution o f the modified Korteweg-de Vries equation. The effects of stochastic relative ve locity on the traffic flow are simulated and analyzed. It is shown that the chan ge rate of velocity in the new model is smaller than that of the Bando's model u nder the same condition and depends on the probability p. As the probability p i ncreases, a small initial disturbance does not magnify and influence on the traf fic flow, but fades away for a long time. The stable region in the new model is larger than in the Bando's model in the phase diagram. The existent initial hyst eresis in the new model will approach to a small region with the increase of tim e in the headway-velocity plot, which is exactly different from that in the Band o's model.In contrast,the hysteresis region in Bando's model will be continuousl y extended to cause traffic flow instability.
Dynamical phase transition and self-organized critical phenomena in the two-dim ensional gas lattice model
2003, 52 (11): 2757-2761. doi: 10.7498/aps.52.2757
A renovated Manna model is studied by computer simulation. The dynamic behavior of the system is changed evidently with the density of particle number.There is a critical particle number density (PND)ρc≈0.684… and critical exp onent α=0.452±0.02 at this density. Self-organized critical phenomena occur only at certain ranges of PND.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2003, 52 (11): 2762-2767. doi: 10.7498/aps.52.2762
Based on the numerical solutions of the generalized Moore's equations, the energy density is studied for the one-dimensional cavity where two boundaries oscillate resonantly. The feature of energy density depends strongly on the frequency, amplitude and dephasing of resonant motions of the boundaries. In some special cases, the packet structure takes place in the energy density.
ATOMIC AND MOLECULAR PHYSICS
Excitation spectra of light from the interaction of highly charged 126Xeq+-ions with solid surface of Ti
2003, 52 (11): 2768-2773. doi: 10.7498/aps.52.2768
The measurement results on 200—1000nm excitation spectra of light from a solid surface of Ti which is excited by slow highly-charged ions(SHCI) 126Xeq+ （6≤q≤30）with a kinetic energy of 150keV are reported. The results s how that the characteristic spectral lines of the target atoms can be effectivel y excited by the SHCI even though the beam intensity of the incident ions is ver y weak (only about one per one nanosecond). We have also found that when the num ber of the peeled electrons of the projectile is beyond a critical value which d epends on the properties of the target, about 20 for Ti, the spectral intensity of the characteristic spectral lines can be greatly enhanced. Theoretical analys es show that this phenomenon is closely related to the surface plasmon excitatio n of the free electron gas of the metal surface during the potential energy rele ase of the single-electron transfer when the number of the peeled electrons is b eyond the critical value.
2003, 52 (11): 2774-2780. doi: 10.7498/aps.52.2774
The dynamics for the D+CD4→CD3+D2reaction have been studied using reduced dimensionality quantum-mechanical theory. By the theory, the reactive polyatomic molecule CD4was treated as a diatomic molecule D—CD 3 , so the system can be treated as a linear atom_diatom reaction, reducing the sy stem to a four_dimensional scattering problem. In calculations, the Hamiltonian of the reaction system has been carried out using the time-dependent wave packet method, and the propagation of wave packets by the split-operator method. The semiempirical potential energy surface which has been developed by Jordan and Gi lbert is employed. The energy dependence of the calculated reaction probability shows oscillatory structures, similar to those observed in abstraction reactions H+H2, H+CH4,etc. The excitation of the stretching vib ration of reac tive molecule D—CD3gives a significant enhancement of reaction pro babilit y, the reaction threshold decreases with the enhancement of the vibrating excita tion. Detailed study of the influence of initial rotational states on reaction p robability shows a strong steric effect. The integral cross sections of translat ional energy for CD4at both v=0 and v=1 at ground rotational state show th at the vibrational excitation significantly enhances the reaction cross section. And the reaction threshold decreases by about 0.2eV, consistent with that of re action probability. The significant enhancement of the reaction probability of r eaction H+CH4at ground state when compared with D+CD4 can be explain ed reasonably in terms of quantum mechanical zero-point energies and the tunneli ng effect.
CLASSICAL AREA OF PHENOMENOLOGY
2003, 52 (11): 2781-2787. doi: 10.7498/aps.52.2781
The study on the light amplification mechanism of iron-doped lithium niobate crystals has been done systematically.The experimental results indicate that the l ight amplification depends on the c-axis direction of the crystal. We propose a new view for the light amplification mechanism of the two-wave mixing in iron-do ped lithium niobate crystals: The diffusion mechanism cannot be neglected, and t he light amplification mechanism in doped lithium niobate crystals is caused by both the diffusion and the transient energy transfer. The decrease of the amplif ied light intensity after the steady-state is due to the decreases of the trans ient energy transfer with time and the energy dissipation caused by the beam fan ning.
2003, 52 (11): 2788-2794. doi: 10.7498/aps.52.2788
By jointly solving the two-centre material equations and the coupled-wave equaions,we set up a dynamic model to study the time-space diffraction properties of the photorefractive volume holograms recorded by two colour light in doubly doped LiNbO3:Fe:Mn crystals.Numerical calculations show that,the time -space diffraction properties of the dynamic volume grating are relevant to the relative spatial phase shift between the index grating and the interference field.The spatial phase shift is defined between -π and π,the energy transferring direction between the two-coupled beams will be reversed with the reversion of the sign of the spatial phase shift.The winding of equal-phase line and the redistributed intensities of the two-coupled beams inside the crystal are given.
A simple optical system consisting of an aperture and a thin lens is considered.It is shown that when a Hermite-Gaussian (H-G) beam is incident on such a type of system and the parameters of the optical system and the beam satisfy a certain condition,a new effect called the focal switch can take place.Detailed numerical results and physical explanation are given to illustrate the characteristics of the focal switch of H-G beams.A comparison with the previous work is made and the potential application of the focal switch is pointed out.
In this letter three photonic logic gate models are presented based on the bacteriorhodopsin(BR) polymer made from variant D96N. With the illumination of 633nm laser the BR molecules can be excited to the M state and show a strong absorption at 412nm, so the intensity of transmitted purple light will decrease until zer o when the exciting light is strong enough. A CCD camera is used to detect t he distribution of transmitted purple light intensity that can be modulated by i llumination of 633nm laser on BR film and NOT, ORNOT, ANDNOT gates are simulated under the special intensity of purple light.
2003, 52 (11): 2807-2810. doi: 10.7498/aps.52.2807
Propagation of a femtosecond THz pulse in random scattering media is described using Monte-Carlo simulation. We study the effects of the radius of scattering spheres and the depth of scattering media, in relation to the parameters of scatt ering coefficient and anisotropic factor by Mie theory. The results show that wh en Mie theory holds, the smaller the spheres, the more the THz pulse is scattere d. The scattering effect expands in the width of pulse in temporal domain and re duces the imaging resolution of THz pulse in random scattering media.
2003, 52 (11): 2811-2817. doi: 10.7498/aps.52.2811
Based on a scalar approximation, the waveguide mode and dispersion property of photonic crystal fibres (PCFs) are investigated with an effective index approach in this paper. It is found that photonic crystal fibres can be single-mode over a very broad spectral range by changing PCFs cladding air-filling fraction or pitch of holes or core diameter. Designing of PCFs can yield zero dispersion at wa velength shorter than 1.27μm and nearly zero flattened dispersion over a very b road spectral range and dispersion compensation with a large normal dispersion.
2003, 52 (11): 2818-2824. doi: 10.7498/aps.52.2818
Using a compact optical link transmission model, the degradation of signal degre e of polarization (DOP) induced by polarization mode dispersion (PMD), especiall y the second-order PMD, and the input signal state of polarization in high-speed optical fibre communication systems is studied in detail. It is pointed out tha t the signal DOP can be used as the feedback control signal in the optical adapt ive first-order PMD optimal compensation systems compatibly. However, if the sec ond-order PMD is considered, the control algorithm will be complicated, and ther e will be the possibility that the system is trapped in a local optimum which wo uld downgrade compensator the performance.
2003, 52 (11): 2825-2830. doi: 10.7498/aps.52.2825
Evolution of pulses obtained by modulating spatial optical solitons in a Kerr no nlinearity planar waveguide with anomalous dispersion is investigated. The pulse s will collapse, self_trapping or divergence according as its initial temporal w idth is more than, equal to or less than the critical value. The higher the orde r of the spatial soliton pulses, the smaller the critical value. The pulse colla pses fastest when its initial temporal width is equal to a special value, and th e more the difference between its initial temporal width and the special value, the slower it collapses. The higher the order of the spatial soliton pulses, th e smaller the special value. The peak power density, temporal and spatial width of the self_trapped pulses differ distinctly from their initial values
2003, 52 (11): 2831-2835. doi: 10.7498/aps.52.2831
We have studied dilepton production during the chemical equilibration of baryon_rich quark_gloun matter, and found that due to the slowing down of the cooling rate and the high initial temperature of the quark_gloun matter(QGM) produced at RHIC energies, the quark phase contribution to dileptons with intermediate mass es is significantly heightened, thus, the enhancement of dileptons with intermed iatc masses should be an signal for the QGM formation. Since this enhancement ca n compensate the dilepton suppression caused by increasing the initial chemical potential, therefore, the dilopton suppression may not be a signal for the quar k_gloun matter formation.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2003, 52 (11): 2836-2841. doi: 10.7498/aps.52.2836
The so_called “phase detune”, caused by nonlinear effects which increase the wavelength of the wake wave, when its amplitude exceeds some limitation, is the m ain saturation mechanism of wake waves in multiple pulse laser wake_field accele rator(MP_LWFA). The MP_LWFA with the optimized spacing between the pulses equal to the wavelength of the wake wave, is studied by PIC simulation in this paper. Our simulation indicates that the detuning length and thus the amplitude of the wake wave increases as our expected. Furthermore, the stronger forward Raman sca ttering is stimulated, which plays an important role in stopping the increase of wake waves.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (11): 2842-2848. doi: 10.7498/aps.52.2842
Simulated annealing algorithm was applied in the decomposition of neutron and x_ray powder diffraction pattern. The method described in this paper has two main advantages: first, the pattern decomposition results do not depend on the starting peak parameters, thus the difficulty in the choice of initial solutions, which occurs in fitting a complex pattern composed of severely overlapped peaks by a conventional least_squares profile fitting method, is overcome; secondly, it has the ability of searching for global other than local optimal solutions, thus can effectively resolve the multi_solution problem mathematically, and this advantage is the most useful when decomposing complex patterns with several local optimal solutions. The computing step is described in detail, the setting of relative parameters is discussed, and the simulated annealing method is compared with a conventional least_squares profile fitting method through both simulated pattern and actual pattern to demonstrate its unique advantage in the decomposition of complex pattern. In principle, the method can also be applied in other kinds of spectra which can be described by profile shape function.
The effect of rapid quenching from melt on Martensitic transition and strain cha racteristics of Ni-Mn-Ga alloy
2003, 52 (11): 2849-2853. doi: 10.7498/aps.52.2849
Ni50Mn27Ga23/sub> alloy was prepared by melt_spinning at wheel velocities of 2,4 and 8m/s separately. The experimental results showed that the rapid quenching caused the decrease of the martensitic transformation temperature an d Curie temperature, while subsequent annealing would increase the depressed val ues. The NiMnGa specimens with a single_phase structure could be obtained more e asily in melt_spun ribbons than in cast alloys. Furthermore, x_ray diffraction s tudies revealed that the main diffraction peak drifted from (220) to (400) in me lt_spun ribbons, which made the texture form, and subsequent annealing made it d isappear. The effects of rapid quenching on the phase_transition strain and magn etic field_induced strain are very complicated. It was found that the phase tran sition strain and magnetic field_induced strain of melt_spun ribbons with textur e were larger than that of cast specimens.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2003, 52 (11): 2854-2858. doi: 10.7498/aps.52.2854
The Tight_binding molecular_dynamics(TBMD) has been used to study the melting behaviour of small silicon clusters Sin（n=5—10）. We report the calcu lated res ults of the latent heat of fusion Δμls and the melting temperature Tm as a function of cluster size. Δμls and Tm exhibit a s trong dependen ce on cluster size. The melting mechanisms of silicon clusters are distinguished from metal clusters. The melting of metal clusters can be described as a tran sition from a low_energy solid_like structure at low temperatures to a higher_en ergy liquid_like structure at high temperatures. At the transition temperature, metal clusters undergo a dynamics coexistence of the two states, while the silic on clusters undergo an intermediate state which is neither liquid_like structure nor solid_like structure. The melting points obtained by using different calcul ation methods and definitions also have been compared in this work.
2003, 52 (11): 2859-2864. doi: 10.7498/aps.52.2859
Two phenomenological models based on the experimental samples of giant magnetoimpedance (GMI) effect are proposed. The first model is a coaxial_cable wire composed of copper cylindrical wire electroplated with a soft magnetic layer, and the second is a sandwiched film structured by two soft magnetic layers, within whic h Cu or Ag serves as the central layer. Their characteristics are discussed theo retically using Maxwell equations and Landau_Lifshitz equation. It is proved tha t for the two models the origination of enhancement of GMI effect is the same, a nd the difference between them arises from the parameter of their geometry. The structure of double deck is better than a single layer for the identical magneti c materials in GMI effect. The application of the theoretical models to real mat erials is examined. Predictions by using the models are qualitatively in agreeme nt with experimental data.
2003, 52 (11): 2865-2869. doi: 10.7498/aps.52.2865
Investigations on the oxygen contamination in the μc_Si∶H thin films deposited by very_high_frequency plasma_enhanced chemical_vapor deposition(VHF_PECVD) technique with and without load lock chamber have been reported in this paper. From the results of x_ray photoelectron spectroscopy and Fourier transform infrared absorption measurements, it can be identified that oxygen exists in μc_Si∶H film with different bonding modes, namely Si—O bonding, O—H bonding and O—O b onding. In addition, the influences of oxygen on the structural and electrical p roperties of the films are studied with Raman spectra, conductivity(σ) and acti vation energy (Ea) measurements. The results reveal that structural propertie s of the μc_Si∶H film depend strongly on the bonding modes of the existing oxy gen. The electrical properties show that the role of oxygen in μc_Si∶H films i s different from those in a_Si∶H and the essential mechanism needs to be furthe r explored.
2003, 52 (11): 2870-2874. doi: 10.7498/aps.52.2870
Starting from the classical equation of motion a dissipation transmission line,the mesoscopic dissipation transmission line is quantized.The quantum effects of the line under excited coherent states are investigated.The results indicate that the quantum fluctuations of the line are not only determined by the circuit parameter and the states of the circuit,but also dependent on the position of the line.
2003, 52 (11): 2875-2878. doi: 10.7498/aps.52.2875
The nc_Si∶H/c_S hetero_junction is fabricated and studied using nc_Si∶H films. Its I_V curves have good thermal stability and change little in the temperature range from 20 to 200℃. The existence of a large amount of interfacial states is resoponsible for the good switch characteristics of the nc_Si∶H/c_Si hetero_junction.
2003, 52 (11): 2879-2882. doi: 10.7498/aps.52.2879
Transport properties of two_dimensional electron gas (2DEG) are crucial to metamorphic high_electron_mobility transistors (MM_HEMT). We have investigated the variations of subband electron mobility and concentration versus temperature from Shubnikov_de Hass oscillations and variable temperature Hall measurements. The results indicate that the electrical performance is the best when the In content is 0.65 in the channel for MM_HEMT. When the In content exceeds 0.65, a large lattice mismatch will cause dislocations and result in the decrease of mobility and the fall of performance in materials and devices.
2003, 52 (11): 2883-2889. doi: 10.7498/aps.52.2883
The accurate first-principle method was used to calculate the electronic structures of eight MgB2 like borides at ambient and under high pressure co nditions. Their electronic structures were compared with each other. The results may be h elpful to modulate physical properties of the borides under high pressure.
2003, 52 (11): 2890-2895. doi: 10.7498/aps.52.2890
Making use of the effective field theory (EFT) and a cutting approximation, in the framework of Ising model, we investigate the thermodynamic properties of a random transverse mixed spin system with a crystal field. Special emphasis is placed on the influence of crystal field, transverse field and random concentration on phase transitions of the system. Our studies find that a smaller crystal field cannot change the percolation threshold of the critical transverse field in the presence of a random transverse field, and that the reentrant phenomena shall appear in the range of random concentration concerned when the transverse field takes a larger value, where as the reentrant phenomena do not occur and when the transverse field takes a smaller value. These new thermodynamic properties have not been reported in previous works so far as we know. We give a series of pha se diagrams and discuss them in detail.
2003, 52 (11): 2896-2990. doi: 10.7498/aps.52.2896
The theory of nonlinear surface spin waves in pure-exchange semi-infinite ferrom agnetic media with inhomogeneous exchange anisotropy has been considered by usin g the Landau-Lifshitz equation. For partly pinned pure-exchange ferromagnet, the boun-dary condition for magnatization of this system is derived, and the nonlinear dispersion relation for these waves is obtained. The one-dimensional(stationary wave along the z-direction) and two-dimensional(2D)(travelling wave in the oxy plane) nonlinear Schrdinger equations which are satisfied by the spin -wave envelope amplitude of the magnetization, are derived. It is shown that the amplitude of the magnetization is determined by the 2D nonlinear Schrdinger e quation. From this, we predict that the nonlinear excitation on the surface of m agnetic materials should be of 2D soliton form. For weakly nonlinear spin waves, the possibi-lity of soliton formation on the basis of 2D nonlinear Schrdi nger equation has been discussed in detail.
2003, 52 (11): 2906-2911. doi: 10.7498/aps.52.2906
Based on the Monte-Carlo simulation, the effects of both the ratio of surface interaction to bulk one Js/J and the multilayered thickness on the cri tical beh avior are studied. It is found that whether the phase transition temperature inc reases with increasing number of multilayers depends on the value of Js/J. Whe n the value of Js/J is above a certain critical value, the system bec omes orde red in the surface before it gets in order in the bulk. Below this critical valu e, one can find that a magnetically disordered surface can coexist with a magnet ically ordered bulk phase. For a small Js/J, the transition temperatu re increa ses slowly with the increase of Js/J and finally are equal to the transiti on temperature of the bulk. When Js/J is large enough, the transition temperat ure increases linearly with the increase of Js/J.The simulated result s are con sistent with those derived by the mean field theory with the transfer matrix met hod, and well explain the experimental facts.
Calculations of the spin-polarization of the electronic current injected from a ferromagnetic metal into a semiconductor
2003, 52 (11): 2912-2917. doi: 10.7498/aps.52.2912
In this paper, we calculate the relationships both between the width of the tunnel barrier and the spin-polarization(SP) of the electronic current when it is injected from a ferromagnetic metal into a semiconductor through a tunnel barrier and between the bias and SP. The results agree with the latest experimental results. We found that a moderate bias and tunnel barrier width allow a giant SP and there is little spin injection at very low bias.
2003, 52 (11): 2918-2922. doi: 10.7498/aps.52.2918
Based on the two-orbital double-exchange model, we discuss the affect of the on- site Coulomb interaction on the orbital ordering in hafl-doped manganites and de rive a formula of the optical conductivity for various phases of half-doped mang anites. The results show that there exists a correlation between the orbital ord ering and the optical absorption. For the magnetic phase (FM), with the transiti on from orbital-disordered to orbital-ordered states induced by the on-site Coul omb interaction(U),the incoherent optical absorption we calculate is substantial ly different. For the layered antiferromagnetic phase (A), the increase of the o n-site Coulomb interaction enlarges the orbital ordering. As a result, the energ y gap in the incoherent absorption is also widened.
2003, 52 (11): 2923-2928. doi: 10.7498/aps.52.2923
Micro-Raman scattaring has been used to study the characteristics of heat conduction on heavy boron-doped Si bridge in an infrared emitter. Based on the proper spectral modeling and the temperature dependence of the position of the Raman peak, the bridge temperature rise due to the heating of high power laser is obtained. Using this method and in the way of point by point, the direct imaging of heat conduction as a distribution map of temperature rise has been also obtained. Compared with the simulated temperature distribution obtained by the finite element software, the experimental and theoretical results are in agreement with each other. While experiments have revealed the local fluctuations of heat conduction in detail, reflecting the nonuniformity of the actual device, and providing experimental bases for the micro-device optimization of the structure design and its fabrication.
2003, 52 (11): 2929-2933. doi: 10.7498/aps.52.2929
A series of samples, prepared from mechanical mixtures of NaCl with NaY zeolite and resulting in the dispersion of NaCl in NaY, was studied by position annihila tion spectroscopy. We measured the positron lifetime spectroscopy as a function of the weight ratio of the NaCl-NaY zeolite heated at 500℃ for 1h, as a function of the heating temperature held for 1h, and as a function of the heating duration at 500℃ for NaCl/NaY(15%). All the lifetime spectra were resolved into five components, in which the third, fourth and fifth components are related to the positron annihilation in β cage, supercage and interface void respectively. The experimental results showed that position annihilation spectroscopy is sensitiv e to the change of the dispersion of NaCl in NaY zeolite.
2003, 52 (11): 2991-2905. doi: 10.7498/aps.52.2991
Based on the micro-rectangle magnetic film system, and the shape and the tilt of crystal easy axis introduced into the Stoner-Wohlfarth model, it was found tha t the expansion of astroid was caused by the size dwindlement of the sample, whi le the defects in shape and the tilt of crystal easy axis would both result in t he formation of asymmetrical astroid. These results illuminated that, in micron order magnetic film systems such as magnetic random access memory, the shape and the tilt of crystal easy axis are important for determining the switch field of the film.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Structual and optoelectronic properties of polycrystalline silicon thin films p repared by hot-wire chemical vapor deposition at low temperatures
2003, 52 (11): 2934-2938. doi: 10.7498/aps.52.2934
Polycrystalline silicon thin films were prepared by hot-wire chemical vapor deposition (HWCVD) on glass at 250℃，with W or Ta wire as the catalyzers. The structual and optoelectronic properties as functions of the filament temperature, deposition pressure and the filament-substrate distance were studied，and the optimized polycrystalline silicon thin films were obtained with Xc>90% (Xc denotes the crystalline ratio of the film), crystal grain size ab out 30—40nm, Rd≈0.8nm/s, σd about 10-7—10-6 Ω-1cm-1,Ea≈0.5eV and Eopt≤1.3eV.
2003, 52 (11): 2939-2940. doi: 10.7498/aps.52.2939
Using the composite graphite rods with the sulphide of iron group metals as anode, the double-wall carbon nanotubes have been fabricated by arc discharging under hydrogen atmosphere. By means of transmission electron microscope, it was found that the double-wall carbon nanotubes were formed in the inner-walls of the evaporation chamber and around the cathode.