Vol. 54, No. 11 (2005)
2005, 54 (11): 4985-4988. doi: 10.7498/aps.54.4985
This paper presents the definition and criterion for holonomic mechanical systems. The Noether conserved quantity, the Hojman conserved quantity and the Lutzky conserved quantity deduced by the Lie-form invariance are obtained. An example is given to illustrate the application of the result.
2005, 54 (11): 4989-4993. doi: 10.7498/aps.54.4989
The planar vibration of a thin elastic rod with circular cross section in viscous medium is discussed. Based on the Kirchhoff's theory the dynamical equations of the rod are established in the Frenet coordinates of the centerline. The torsional vibration is decoupled from the flexural vibration when the centerline is an arbitrary planar curve. The planar torsional vibration of an arbitrary planar rod and the planar flexural vibrations of an axially compressed straight rod and a ring without torsion are discussed when the ends of the rod are fixed. The natural frequencies and the damping coefficients are derived. It is proved that the Lyapunovs and Eulers conditions of stability of an axially compressed straight rod in the space domain are the sufficient and necessary condition of asymptotic stability of the rod in the time domain, or the necessary condition of stability of the rod without damping. The asymptotic stability of a ring in viscous medium is always satisfied.
2005, 54 (11): 4994-4998. doi: 10.7498/aps.54.4994
The hyperbolic complex space RH defined by the Clifford algebra and the hyperbolic phase transformation group U4(H) acting on RH are endowed with definite physical meaning in this paper. The hyperbolic complex space RH is isomorphic to the 4-dimensional(4D) Minkowski spacetime, and the hyperbolic phase transformation group U4(H) in RH is just Lorentz transformation group on 4D relativistic spacetime. Furthermore, the general expressions of Lorentz transformation and the velocity transformation on 4D Minkowski spacetime are naturally derived using the composite transformations of the group U4(H). Hence, the well-known special Lorentz transformation in the special relativity(SR) is contained as a special case in our discussions.
2005, 54 (11): 4999-5002. doi: 10.7498/aps.54.4999
With the help of the general Sine-Gordon travelling wave transformation equation, we present a new method for solving the variable coefficient KP equation, and successfully obtain the new solitary wave-like solution, the Jacobi elliptic function-like solution and trigonometric function solution of variable coefficient KP equation.
2005, 54 (11): 5003-5013. doi: 10.7498/aps.54.5003
Self-trapping of Bose-Einstein condensates (BEC) in double-well trap is investigated. Two kinds of self-trapping are discussed through phase space analysis in the mean-field approximation: 1) The number of atoms oscillates near an equilibrium point in the phase space, while relative phase increases monotonously with time (running-phase); 2) Both the number of particles and the relative phase oscillate near an equilibrium point in the phase space. In particular, we investigate how an external periodic filed influence the self-trapping. It is found that the external periodic field may dramatically modulate the critical points at which the transition to self-trapping occurs. With this, we can observe self-trapping phenomenon in a dilute Bose-Einstein condensate with a very weak interaction as well. Finally, the effect of many-body quantum fluctuation on self-trapping is also studied. We also discuss how to observe the self-trapping phenomenon with present experimental techniques.
2005, 54 (11): 5014-5017. doi: 10.7498/aps.54.5014
We present a quantum key distribution system based on two polarization beam splitters, by means of which the phase modulator's polarization dependence is cancelled out. A high key generation rate has been obtained for the first time at 1310nm transmitted over a 25 km long fiber, with a fringe visibility of 99.4%. A sifted key rate of about 0.6 kbits/s and quantum bit error rate of about 0.5% are obtained.
Using quantum tunneling method Hawking radiation of a static black hole horizon with a mass-quadrupole moment is studied
2005, 54 (11): 5018-5021. doi: 10.7498/aps.54.5018
This paper presents a straightforward derivation of Hawking radiation from a static black hole possessing mass-quadrupole moment as a tunneling process,and the radiation spectrum is obtained.Because the derivation assumes conservation laws,the exact spectrum is not precisely thermal. This result supports the viewpoint that it is possible for the radiation via tunneling to have information-carrying capabilities.
2005, 54 (11): 5022-5026. doi: 10.7498/aps.54.5022
Stroboscopic maps for voltage-mode converters in the continuous conduction mode (CCM) are build up. The stability of one-periodic point is analyzed together with eigenvalues of Jacobian matrix of discrete-maps. The voltage-mode buck converter is taken as an example, and the results of theoretical analysis and numerical simulation coincide with each other, which shows that the stability analysis of the DC-DC converters is feasible using the discrete-map model.
2005, 54 (11): 5027-5033. doi: 10.7498/aps.54.5027
The stochastic resonance (SR) is studied in an overdamped linear system when the bias-signal-modulated noise is introduced. The exact expressions of the first two moments and signal-to-noise ratio(SNR) are obtained when we introduce the asymmetric dichotomous noise into the system. We find that the system has three different forms of SR: the conventional SR, the bona fide SR and SR in the broad sense. Moreover, the additive noise weakens the SNR of the linear system while the cross-correlation enhances the SNR and improves the output signal.
2005, 54 (11): 5034-5038. doi: 10.7498/aps.54.5034
A neuro-fuzzy approach based on a novel hybrid learning method is presented, which can generate the best fuzzy rule set automatically from the desired input-output data pairs only and can give the initial neuro-fuzzy system and the initial parameters of fuzzy membership functions. Then the parameters of fuzzy membership functions and the weights can be easily tuned by employing neural network's self-learning techniques. This approach reduces the rule matching time and accelerates the speed of the fuzzy logic referencing and improves the adaptability of the neuro-fuzzy system. Using the proposed neuro-fuzzy system and the learning algorithms we simulated the prediction of the Lorenz chaotic time series, the results demonstrate the effectiveness of the chaotic time series prediction approach.
2005, 54 (11): 5039-5047. doi: 10.7498/aps.54.5039
At present time, only necessary conditions of chaotic synchronization are known, and applications of chaotic synchronization is limited. In this paper, sufficient conditions of continuous chaotic system synchronization and the proofs are presented, and evolutive range of state variables is presented, too. We proved the conditions are realizable. As an application of the theory, we proved sufficient conditions of time-varying parameter chaotic synchronization, and made simulations by Chua circuits. Time varying parameter chaotic synchronization communication has high security performance, and the simulations that it defeat all kinds of attacks of eavesdroppers are presented.
2005, 54 (11): 5048-5052. doi: 10.7498/aps.54.5048
This paper reports a new chaotic circuit, which consists of only a few OpAmps, capacitors, and resistors. The chaotic attractor obtained via computer simulation, has one positive Lyapunov exponent. To supplement the computer simulation, a physical circuit implementation is designed. Some experimental results are given.
2005, 54 (11): 5053-5057. doi: 10.7498/aps.54.5053
A method of chaos control using time-delay nonlinear feedback based on stability criterion is proposed. By a suitable separation of the chaotic system, a special nonlinear function is obtained. We use the difference of nonlinear functions of the chaotic output signal and its delayed output signal to construct a continuous feedback input perturbation. The method can stabilize chaotic systems to a desired periodic orbit without using any external force. The method retains the advantages of performing the self-control via delayed feedback control method. Besides, the validity of control is ensured due to the stability criterion. The control can be started at any moment, and it is convenient and flexible. The coupled Duffing oscillator is given as numerical examples. The results of numerical simulation show the validity of the method.
2005, 54 (11): 5058-5061. doi: 10.7498/aps.54.5058
The speed feedback synchronization of a chaotic system has been studied by using linear feedback synchronization, generalized synchronization and coupled synchronization methods. The coefficients of speed feedback synchronization have been figured out and are smaller than those of the general feedback synchronization, so the complexity and cost is reduced. Numerical simulations show the effectiveness of the methods.
2005, 54 (11): 5062-5068. doi: 10.7498/aps.54.5062
A non-linear predictable global model for chaotic time series is built based on continued fractions after developing the method of polynomial approximants in theory. We can analyze the characteristics and realize the prediction by substituting the model for the equation of chaotic time series. The results of theoretical analysis and computer simulation have proved this method to be practically feasible for predicting a chaotic series accurately and give its explicit expression.
Application of homotopy technique with the parameter expansion to strongly nonlinear stochastic dynamic systems
2005, 54 (11): 5069-5076. doi: 10.7498/aps.54.5069
This paper extends the method of PE-HAM to strongly nonlinear stochastic dynamic system under harmonic and Gauss white noise excitations. By constructing an appropriate homotopy mapping, the original system is transformed into a set of linear stochastic differential equations. In addition, the strongly nonlinear Duffing oscillator subjected to harmonic and Gauss white noise excitations is investigated using the proposed method, and its approximate analytically solution process and steady-state probability density are obtained. Numerical simulation is employed to verify the theoretical result and good agreement is found.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (11): 5077-5081. doi: 10.7498/aps.54.5077
With many-body perturbation theory (MBPT), 1D—3D term intervals of helium 1snd(n=4—11) configurations have been calculated. Based on two different models, Rayleigh-Schrdinger perturbation expansion terms only consisting of bound states and those of continua are calculated respectively. For bound states, the zeroth-order wave functions are strictly generated from self-iteration solutions of Hartree equation and residues of infinite perturbation series are dealt with by integral processing method. For continuum parts, a simplified hydrogen potential model is adopted. According to Rayleigh-Schrdinger expansion, the perturbation corrections to Rydberg states have been evaluated up to the third-order terms. From the calculation, the energy splittings are mainly attributed to bound parts. Singlet-triplet level splittings yielded here are found to agree quite well with two sets of experimental results.
2005, 54 (11): 5082-5088. doi: 10.7498/aps.54.5082
With self-consistent iterative method for solving the Hartree equation, precise numerical wavefunctions of helium 1snl configuration are generated to build up the LS term wavefunctions as basis sets. The magnetic fine structure of helium 10G—10M Rydberg states is calculated with the linear variation method, including both the exchange and magnetic interaction under the Breit-Bethe approximation. The calculated results agree well with the existing experiment data. Some ideas and discussions for further improvement are given.
2005, 54 (11): 5089-5092. doi: 10.7498/aps.54.5089
Nanosized BaTiO3 coated with dodecybensulphonic acid (DBS) and stearic acid (St) was prepared using the hydrothermal procedure. The average size of DBS/BaTiO3 and St/BaTiO3 is about 60nm, much smaller than the that of 100nm of the uncoated particles prepared under similar conditions. Raman spectra from the coated particles were measured, and scattering signals from both BaTiO3 and the coatings were observed. It was found that the Raman peaks of BaTiO3 shift toward higher frequency(blue shift), instead of the red shift generally observed when the particle size is reduced, and the linewidth increases when the grain is coated. Meanwhile, we found that different coating show different amount of Raman shifts. We discussed the possible origin of the blue shift.
Effect of external magnetic field on the coherence properties of degenerated two-level atomic system
2005, 54 (11): 5093-5097. doi: 10.7498/aps.54.5093
The electromagnatically induced absorption (EIA) is obtained in degenerated cycled cesium atomic two-level transition of 6S1/2F=4—6P3/2F'=5. The effect of the magnetic field on coherence of the atom is also investigated experimentally. When external magnetic field is applied, the mixed structure of electromagnetically induced absorption and transparency is obtained in the transition of 6S1/2F=4—6P3/2F'=5. The experimental results are in agreement with theoretical analysis of C.Y. Ye et al. (2002).
2005, 54 (11): 5098-5103. doi: 10.7498/aps.54.5098
Photoionization of CS2 clusters seeded in helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd: YAG laser beam of intensity about 8×1010 W/cm2. Multiply charged ions of C2+, S2+ of hundreds of eV have been observed when the laser beam irradiates the most dense portion of the pulsed molecular beam. An electron re-scattering and re-colliding ionization model is proposed to explain the appearance of the multiply charged clusters under such low laser intensity.
Temperature measurement of cold atoms in a cesium magneto-optical trap by means of short-distance time-of-flight absorption spectrum
2005, 54 (11): 5104-5108. doi: 10.7498/aps.54.5104
We report the basic idea and experimental demonstration of measuring the temperature of cold cesium atomic cloud confined in a magneto-optical trap (MOT) by analyzing absorption spectrum observed in the short-distance time-of-flight (TOF) method. Compared with the conventional TOF scheme, we measure the temperature of cold atomic cloud in MOT by short-distance TOF method for our small vapor cell. If the cold atomic cloud is released, it will fall and expand due to gravity and its initial velocity distribution. Utilizing a cylindrical resonant probe beam positioned several millimeters beneath the MOT (in this paper, we analyzed the cases for 3mm, 5mm, and 8mm of center-to-center distance between the MOT region and the probe beam, respectively), we can record the short-distance TOF absorption spectrum with a photodiode when cold atoms go through the probe region. Analysis of the short-distance TOF absorption spectrum yields the effective temperature of the cold cloud in MOT.
2005, 54 (11): 5109-5115. doi: 10.7498/aps.54.5109
In this paper, we propose a new scheme to form an array of surface hollow optical micro-traps for cold atoms (or molecules) by using a phase grating with four phase steps and an array of microlens, study the intensity distribution of 2D array of surface hollow optical micro-traps, and calculate the corresponding optical potential for cold 85Rb atoms, and discuss some potential applications of our hollow micro-trap array in atom and molecule optics. Our study shows that when our grating-lens system is illuminated by YAG laser with a power of 1W, a 2D array of surface hollow optical traps with 104 micro-wells will be generated in an area of 1cm2. Each optical trap has some novel characteristics, such as smaller trapping volume, higher effective intensity and its intensity gradient. The corresponding optical potential for trapped 85Rb atoms can reach 190μK, which is high enough to trap cold atoms or cold molecules, and can be used to realize an all-optical atomic and molecular Bose-Einstein condensations, even to prepare novel optical lattices, and so on.
2005, 54 (11): 5116-5120. doi: 10.7498/aps.54.5116
We theoretically study the photon counting statistics characterizations of the real single molecular photon source with a Poisson statistics background and that of an ideal double molecular system based on the standard HBT detection. Mandel parameter Q of each source with the same mean photons n—was analyzed. We have obtained an efficient method to identify single molecule by the two-photon statistics probability P(2), which shows the relation P(2)2. Additionally, we studied the effect of single-to-background ratio of the single molecular photon source on the criterion.
2005, 54 (11): 5121-5125. doi: 10.7498/aps.54.5121
The orientation parameter is used to describe the collision dynamic process and the structure informations of excited atomic state in electron scattering. In density matrix theory, the state multipoles express the structure of atom assembles impacted by particles, and the state multipole of K=1 expresses the orientation vector. In the sysmetry scattering plane system, the orientation vector is denoted by the orientation parameter L⊥, which is calculated from scattering amplititutes, C-G coefficient and 6-j symbol. The orientation parameters of sodium S→P excited by low energy electron are calculated in this paper, and the results are consistent with that obtained from electron-photon coincidence scattering experiment from 2eV—100eV incident energy. The characteristics of orientation angular-distribution vs incident energy are also discussed.
2005, 54 (11): 5126-5129. doi: 10.7498/aps.54.5126
The equilibrium geometrical structures of ground state of small Yn(n＝2—8) clusters are optimized by mean of density functional theory(DFT), and the ionization potentials are calculated. The results show that the most stable structures of clusters tend to maximize the average coordination number of Y atoms. The value of ionization potential shows uo magic number or odd-even alternations, this would imply that the threshold for photoionization occurs mainly from a localized 4d orbital rather than from a 5s orbital of Y clusters. It is the first time to come up with a modification of the analytical formula of calculating ionization potential of Y clusters proposed by Tomasz, and the new analytical formula is in better agreement with experiment.
CLASSICAL AREA OF PHENOMENOLOGY
Electromagnetic scattering interaction between a conducting plate and a 2-D conducting slightly rough surface
2005, 54 (11): 5130-5138. doi: 10.7498/aps.54.5130
Electromagnetic scattering with interaction between the perfect conducting plate and the 2-D conducting slightly rough surface is investigated. Taking the advantage of s newly developed technique that utilizes the reciprocity theorem, the difficulty in formulating the secondary scattered fields from the composite target is reduced to the evaluation of integral equation involving the polarization currents of the conducting plate and the scattered fields from the slightly rough surface. The polarization currents on the plate and the electromagnetic scattering field are solved by using physical optics approximation and small perturbation method, respectively, and the solution for the composite scattering cross section is obtained and calculated. In particular, the results of backscattering from the composite mode are discussed in detail.
2005, 54 (11): 5139-5143. doi: 10.7498/aps.54.5139
We present an approach to expand the shaped beam in terms of the spheroidal wavefunctions in spheroidal coordinates for a spheroidal particle illuminated by off-axis arbitrarily shaped beam. The relations between shaped beam coefficients in spherical coordinates and the different range of mode are discussed. Once the beam-shape coefficients are determined, the solution of scattering for arbitrarily shaped beam by a homogeneous particle can be obtained.
2005, 54 (11): 5144-5148. doi: 10.7498/aps.54.5144
Based on the vectorial Rayleigh-Sommerfeld diffraction formulation, a solution of the electric-magnetic wave equation is found, which represents vectorial nonparaxial off-axis Gaussian-beams whose propagation equation in free space is expressed in a closed form. The on-axis and far-field expressions of vectorial nonparaxial off-axis Gaussian beams, the propagation equation of vectorial nonparaxial Gaussian beams and the paraxial results are treated as special cases of our general expression. It is shown that the f parameter plays an impotant role in determining the beam nonparaxiality, whereas the off-axis parameters additionally affect the nonparaxial behavior of vectorial nonparaxial off-axis Gaussian beams. Moreover, unlike the on-axis case, there exists the longitudinal component of the field in the y direction for the off-axis case.
Fine tracking plays an important role in space laser communication, and the Fine Pointing Mirror(FSM) is a key component in fine tracking system. Based on the optical vector reflection law, the accurate optical characteristics of FSM is deduced, which serves as the theoretical basis for fine tracking study. A fine tracking control system based on the FSM accurate optical characteristic is introduced. For system regulation, two important improvements to the simplex method are obtained. Then a digital simulation of the fine tracking is given. So an accurate control of the FSM is accomplished and the accuracy of the fine tracking system is improved. The diffractive superresolution theory is introduced into the space laser communication. By using 3-zone phase pupil filter, the point spread function (PSF) of the optical system is modified, and the optical energy distribution at the focal plane is modified accordingly. Then the diffraction spot size is decreased, and the optical resolution is increased, so the accucy of the fine tracking system is improved.
2005, 54 (11): 5157-5163. doi: 10.7498/aps.54.5157
A new approach based on phase features combined with neural network model is proposed for recognizing 3-D objects. The phase features of an object were extracted by wavelength-scanning digital holography and numerical reconstruction technique. A BP neural network with one hidden-layer trained by reconstructed images of three pyramids was used to recognize other pyramids with some variance, and the correct recognition rate of these pyramids is up to 100%. The simulation results demonstrate that the method is effective.
Theoretical analysis of the five-mirror femtosecond Ti:sapphire oscillator containing a semiconductor saturable absorber mirror with negative Kerr effect
2005, 54 (11): 5164-5167. doi: 10.7498/aps.54.5164
The five-mirror laser cavity containing a semiconductor saturable absorber mirror (SESAM) with negative Kerr effect is theoretically analyzed for the first time. It shows that, compared with the cavity without a SESAM, the upper stable range of the resonator expands obviously after the introduction of SESAM. This indicates that the work point for self-starting can be more close to the edge of the stable range of the CW state, and then get higher nonlinear effect. This shows that the negative Kerr effect of the SESAM can contribute to the self-starting of the modelocked laser besides the saturable absorption mechanism.
Third-order nonlinear optical properties of bromo［tri-α-(2,4-dimethyl-3-pentyloxy) subphthalocyanine］ boron
2005, 54 (11): 5168-5172. doi: 10.7498/aps.54.5168
The third-order nonlinear optical properties of a new subphthalocyanine complexe (bromo［tri-α-(2,4-dimethyl-3-pentyloxy) subphthalocyanine］ boron) was studied by Z-scan using 8ns laser pulses at 532nm. It was found that the compound shows a strong reverse saturation absorption (β=3.7×10-10 m/W) and nonlinear self-focusing refraction effects (n2=7.2×10-11 esu). The third-order nonlinear susceptibility (χ(3)) is 1.1×10-11esu.The effects of cone-chaped molecular structure and axially heavy-atom (Br) substitution on third-order nonlinear optical properties are also discussed.
Three-photon-absorption induced fluorescence and optical limiting properties of a new organic compound
2005, 54 (11): 5173-5177. doi: 10.7498/aps.54.5173
Three-photon-absorption-induced frequency up-conversion fluorescence emission has been observed in a solution of 4-2-(7-(4-amido styrene)-9,9-di(2-ethyl hexyl)-9H-fluorene-2-) ethylene) aniline (BASF) in N,N-dimethylformamide(DMF), pumped with 38ps Q-switched 1064nm laser pulses. The spectral peak of the observed fluorescence emission is located in the 456—775nm range, and the intensity dependence of the visible emission on the IR excitation obeys the cubic law. At higher solute concentration and moderate IR excitation intensity levels, obvious optical limitation behavior has been observed due to three-photon-absorption. The measured nonlinear absorption coefficient and the molecular three-photon-absorption cross section are 4.34×10-20cm3/Ｗ2 and 2.4×10-39cm6/Ｗ2, respectively.
2005, 54 (11): 5178-5183. doi: 10.7498/aps.54.5178
We have experimentally demonstrated the self-compression of gegawatt high power femtosecond laser pulses in normally dispersive solid bulk media. It was proved that high-power femtosecond laser pulses can be compressed during the self-focusing propagation in the transparent nonlinear medium. The self-compression behavior was investigated in detail under a variety of experimental conditions, and the temporal and spectral characteristics of resulted pulses are found to be significantly affected by the input pulse intensity, with higher intensity corresponding to shorter compressed pulse. However, the output pulse is split into two peaks when the input intensity is high enough to lead to supercontinuum and conical emission. By the propagation in a piece of BK7 glass, a self-compression from 50fs to 20fs is achieved, with a compression factor of about 2.5. Moreover, we find that pulse self-compression can be achieved with a divergent input laser beam into the glass.
2005, 54 (11): 5184-5188. doi: 10.7498/aps.54.5184
Stable self-starting mode-locking states in a compact Ti: sapphire laser incorporating a home-made SBR with low loss double quantum-well and low temperature and surface state hybrid absorber are investigated experimentally. The three mode-locking states, i.e. the passive mode-locking with a saturable absorber, the solition mode-locking and the Kerr-lens mode-locking have been successfully demonstrated. In this laser, chirped mirrors are used for dispersion compensation, and the 18 fs pulses are produced from the Kerr-lens mode-locking at 4.5W pump power, and output power is 150mW.
2005, 54 (11): 5189-5193. doi: 10.7498/aps.54.5189
This paper discusses the optical beam (1+2D) of suitable input power propagating in the strong nolocal nonlinear media,which is governed by the Snyder-Mitchell model in the cylindrical coordinate.An exact analytical solution in Laguerre-Gaussian form is obtained.It is shown that the solution in the Gaussian form is the lowest-order mode.It is found for the first time that the necklace-ring spatial soliton exists in the strong nonlocal media.
2005, 54 (11): 5194-5200. doi: 10.7498/aps.54.5194
Strong optical spatial solitons are solitons that satisfy the strong nonlocal condition.We discuss the nonplanar interaction of a pair of (1+2)D optical spatial solitons with symmetrical oblique incidence on the basis of Snyder and Mitchell's revolutionary work［Accessible solitons.Science,1997,276(6):1538—1541］.An accurate analytical solution in Gaussian form is obtained for the first time.It is shown that rrapping of two beams in a stable spiraling is possible for a large range of parameters.The spiraling structure does not depend on the initial relative phase.The projection of the wto beam centers in the transverse coordinate plane lies always in the same ellipse.It is possible to find its applications in planar all-optical swithching and all-optical interconnection in bulk media.
2005, 54 (11): 5201-5209. doi: 10.7498/aps.54.5201
The propagation of two orthogonally polarized coaxial light beams in plannar waveguides is studied by variational approach as well as numerical method. The condition for soliton-like mutually-trapped propagation of the two beams is obtained. We analysed the different characteristics of mutually-trapped propagation in two cases with or without linear birefringence. We find that there is an essential difference between mutually-trapping beams and the rigorous vector spatial soliton.
Optical properties of surface plasmons induced by the plan of a periodically arranged dielectric spheres on the metal slab
2005, 54 (11): 5210-5217. doi: 10.7498/aps.54.5210
Optical properties of a system composed of a metal slab with two planes of periodically arranged dielectric spheres on the metal surface have been investigated.The results obtained from multiple scattering method show that the periodic dielectric spheres on the upper surface of the metal could induce surface plasmons on the metal-dielectric interface.For a very thick metal slab,the existence of the surface plasmons can be observed by corresponding peaks in absorption spectrum.The position of the absorption peak is mainly determined by the periodicity ofdielectric spheres,and is consistent with the analytic theory very well.For the limited thickness of metal slab,there exist two surface plasmon modes,corresponding to symmetric and antisymmetric modes,respectively,and the absorption peak that occurs in the thick metal slab splits into a double-peak strurcture.For a symmetric or antisymmetric surface plasmon,the magnitudes of the electric and magnetic fields are the same on both sides of the metal slab,thus these surface plasmons can results in a strong transmittance.The plane of periodically arranged dielectric spheres beneath the metal slab can lead the surface field out of the metal,and form a transmission plane wave.The results obtained from multiple scattering method show that the transmittance is fairly high when surface plasmons exist.The fundamental physical mechanism is studied in detail,and the occurrence of the surface plasmons,and hence the position of the peak of absorbance or transmittance,can be controlled by adjusting corresponding parameters in the system.
Application of dispersion compensator based on chirped fiber gratings in ultra long-hual DWDM system
2005, 54 (11): 5218-5223. doi: 10.7498/aps.54.5218
An application of chirped fiber grating in an ultra long-hual DWDM system is presented in the paper. The interaction between the chirped fiber gratings at different wavelengths are analyzed for the first time. A method of prolonging the distance between gratings to surpass the coherent length of the light source is proposed to suppress the interaction between the gratings. By using chirped fiber gratings, we realized a transmission system of 8×10Gbit/s signal on G.652 fiber over 1500km.
2005, 54 (11): 5224-5227. doi: 10.7498/aps.54.5224
The application of the wavelet-transform to terahertz time-domain spectroscopy (THz-TDS) is described. Using wavelet-transform to analyze the time-domain signals passing through water vapor measured by time-domain spectroscopy, we got the absorption spectra of water vapor in the frequency range from 0.5 to 2.5THz, which agree well with the results reported in the literature. Moreover, wavelet-transform in THz-TDS opens up a new way for the analysis of the time-domain properties of absorption spectra of water vapor.
2005, 54 (11): 5228-5232. doi: 10.7498/aps.54.5228
The gain characteristics of Er3+/Yb3+-codoped phosphate fiber amplifier pumped with light of 980nm wavelength are theoretically studied in this paper. With the help of rate equations and the propagation equation of Er3+/Yb3+-codoped phosphate fiber, we analyzed the effects of concentration of erbium and ytterbium ions, pump power, signal power and fiber length on the gain characteristics of the co-doped fiber amplifier. Comparison with singly erbium-doped fiber amplifier was also made. It is shown that the sensitization of Yb3+ decreases the clustering effect of erbium ions in the fiber and the gain and pump efficiency of Er3+/Yb3+ co-doped fiber are apparently higher than that of singly erbium-doped fiber. Numerical results also demonstrate that considerable signal gain of 10dB can be achieved in a 3.2cm-long fiber amplifier with 20dBm(100mW) pumping power at 980 nm.
Theoretical and experimental research on the second harmonic of focused ultrasound in layered biological media
2005, 54 (11): 5233-5238. doi: 10.7498/aps.54.5233
Based on the Khokhlov-Zabolotkaya-Kuznetsov (KZK) equation in frequency-domain, a theoretical model of focused ultrasonic waves in the layered biological medium with consideration of the sound absorption, nonlinearity, boundary of the media and the diffraction of the source is presented. The propagation of focused ultrasonic waves for fundamental and second harmonic in the multi-layered biological media are numerically studied and compared with the experimental results. Good agreement of the theory with the measurement shows that this approach can effectively describe the second harmonic sound field in multi-layered biological media.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (11): 5239-5245. doi: 10.7498/aps.54.5239
Based on the Maxwell equations, the general equation of the slow-wave structure filled with plasma in the finite magnetic field is derived. The dispersion equation and interaction impedance expression of the disk-loaded waveguide filled with plasma in the strong longitudinal magnetic field are studied. The result shows that the frequency of the TM01 mode upshifts and interaction impedance increases as the density of the plasma increases. When a periodic structure is loaded with plasma, the spectrum consists of abundant TG modes (Trivelpiece-Gould modes). As the plasma density increases to a certain degree, the TM01 mode of the disk-loaded waveguide overlaps the TG mode and these two modes will couple with each other and form the new hybrid modes G1, G2. If the relativistic Traveling-Wave Tube (TWT) works on the hybrid mode, there will be new working mechanism.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (11): 5246-5250. doi: 10.7498/aps.54.5246
A series of Er３(Fe, Co, M)２９ (M=Cr, V, Ti, Mn, Ga, Nb) compounds has been synthesized and their structure and magnetic properties have been investigates by means of x-ray diffraction and magnetic measurements. It is found that the Fe-based Er３(Fe,M)２９ compounds crystallize in the Th2Ni17-type structure with disordered substitution of the dumbbell Fe-Fe, instead of Nd3(Fe,Ti)２９-type structure, so its chemical formula can also be expressed as Er2－n(Fe,M)17+2n (n=0.2). Substitution of M for Fe in the Er３Fe29 compound leads to an increase in the Curie temperature. With the substitution of Co for Fe in the Er３(Fe,M)２９ (M=Cr, V) compounds, a new phase was found which crystallizes in monoclinic symmetry. The anisotropy of the Er３Fe19.5Co6V3.5 compound at room temperature is of easy-axis type and a spin reorientation transition from the easy-axis type to the easy-plane type anisotropy occurs when temperature decreases to 162K. A first order magnetization process (FOMP) was observed in the HMD magnetization curve of Er３Fe19.5Co6V3.5 at 5K, the critical field of the FOMP was derived to be 3.8T.
2005, 54 (11): 5251-5256. doi: 10.7498/aps.54.5251
The conductance of quantum point contact in scanning tunneling microscope is calculated by modal matching and scattering matrix method. The results show that the conductance of the nano-structure formed during quantum point contact in STM is quantized, which becomes more obvious as the radius and cone angle of the nano-structure decreases. The quantitative behavior could be observed more easily with semiconductors than with metals.
Preparation, structural characterization and nitrogen adsorption properties of a self-supported nanostructured gold film
2005, 54 (11): 5257-5261. doi: 10.7498/aps.54.5257
Employing silicon nanoporous pillar array (Si-NPA), a novel silicon micron/nanometer complex systems as reducing substrate, a self-supported, nanostructured gold film was prepared by immersion technique. The microstructure and surface morphology of the film were characterized. Our experiments disclosed that the preparation of the film is a self-stop process. With the exhaustion of Si-NPA, the chemical reducing reaction related with the Au3+ ions occurring in the immersing solution would stop automatically, and the deposited nanostructured gold film would disengage from the substrate to form a self-supported thin film. The formation mechanism of the film is due to the high surface reactivity and strong chemical reducibility of Si-NPA. The elemental composition analysis by energy dispersive x-ray spectroscopy showed that the prepared gold film exhibits strong capability in nitrogen adsorption and storage, which may find potential applications in the technical fields of gas sensors, air separation, nitrogen purification and membrane synthesis of various nitrides.
2005, 54 (11): 5262-5268. doi: 10.7498/aps.54.5262
A study based on non-resonant bond polrizability model is maded on the Raman scattering intensity of single-wall carbon nanotube.The structure of nanotube,polarization of light and sample orientation dependence of the Raman intensity was discussed by varying the direction of the nanotube axis.It is found that the polarization of light have large effect on the Raman spectra,while the chirality of the carbon nanotube has little effect.The chirality and diameter dependence of the Raman intensity were calculated using the theory of randomly oriented particles.
2005, 54 (11): 5269-5273. doi: 10.7498/aps.54.5269
In the interaction process of a swift heavy ion (SHI) and polymer, a latent track with radius of several nanometers appears near the ion trajectory due to the dense ionization and excitation. To describe the role of electronic energy loss (dE/dX)e, multi-layer stacks (with different dE/dX) of polyimide (PI) films were irradiated by different SHIs (1.158GeV Fe56 and 1.755GeV Xe136) under vacuum at room temperature. Chemical changes of modified PI films were studied by Fourier Transform Infrared (FTIR) spectroscopy. The main feature of SHI irradiation is the degradation of the functional group and creation of alkyne. The chain disruption rate of PI was investigated in the fluence range from 1×1011 to 6×1012 ions/cm2 and a wider energy stopping power range (2.2 to 5.2 keV/nm for Fe56 ions and 8.6 to 11.3 keV/nm for Xe136 ions). Alkyne formation was observed over the electronic energy loss range of interest. Assuming the saturated track model (the damage process only occur in a cylinder of area σ), the mean degradation and alkyne formation radii in tracks were deduced for Fe and Xe ion irradiation, respectively. The results were validated by the thermal spike model and the threshold electronic energy loss of track formation Set in PI was deduced. The analysis of the irradiated PI films shows that the predictions of the thermal spike model are in qualitative agreement with the curve shape of experimental results.
Based on multiscale concurrent algorithm, we have implemented a unified dynamics scheme and investigated displacement distribution, oscillation behavior, energy fluctuation, charge density difference and the effect of environment of single vacancy system. The displacement distribution and the related behavior reflect the quantum effect of single vacancy. At the same time, the calculations of the total energy and charge density difference revealed the effect of environment and indicated the coupling between the classical and quantum effects.
Study of structure optimization of carbon nanotubes using hybrid genetic algorithm based on clonal selection principle
2005, 54 (11): 5281-5287. doi: 10.7498/aps.54.5281
Focusing on the problem of carbon nanotube structure optimization by molecule dynamics simulation, a novel algorithm is proposed which combines the genetic algorithm with simulated annealing and the clone select algorithm.Test results of five typical functions show that this algorithm has high stability and gives good global optimization. Applied to structure optimization of carbon nanotubes, it can accelerate the process of energy optimization and improve the quality of structure optimization.The simulation results show that the optimizing time increases linearly with the number of atoms.The time of structure optimization is reduced one order of maguitucle compared with the conjugate gradient methods.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
A study on the mechanism of the influence of Bi, Sb alloying on microstructure and properties of AZ91 magnesium alloy
2005, 54 (11): 5288-5292. doi: 10.7498/aps.54.5288
The atomic structure model of symmetric ［0001］tilt boundary of α phase in AZ91 magnesium alloy was set up by using the concept of coincidence-site lattice (CSL). The total structure energies of α matrix and grain boundary (GB), the environment sensitive embedding energies (EESE) and the interaction energies of Al, Bi and Sb were calculated by using recursion method. The alloying behaviour of Al, Bi, Sb in AZ91 magnesium alloy was discussed. Calculation results show that the total structure energies of α matrix and grain boundary (GB) are decreased due to the presence of Al, Bi or Sb, which suggests AZ91 alloy is strengthened due to solid solution strengthening. Alloying elements tend to be distributed uniformly in α matrix, and are apt to occupy the top sites of the trigonal prism formed by Mg in the GB core. The aggregation of Bi or Sb to GBs,being easier than Al, suppresses the aggregation of Al, which accelerates the formation of continuous precipitates, improves the high temperature properties. The major alloying element Al and the additional elements Bi or Sb in small amounts can form the ordered phases in AZ91 alloys: Mg１７Al１２, Mg3Bi2 and Mg３Sb２, respectively, and the quantity of the ordered phase is greater in GBs than in α(Mg) matrix. Bi or Sb additions to AZ91 retards the aggregation of Al, and Mg3Bi2 or Mg３Sb２ precipitates along boundaries greatly improve the high temperature properties.
First-principle calculations of structural properties and effective-mass of zinc-blende ZnTe and CdTe
2005, 54 (11): 5293-5300. doi: 10.7498/aps.54.5293
The electronic band structures of zinc-blende ZnTe and CdTe are calculated by using a self-consistent full-potential linearized augmented plane-wave method within the first-principle formalism. In order to clarify the electronic properties near the Brillouin-zone (BZ) center and give an effective guideline on the material design for electronic and optical devices, we link the first-principle band calculations with the effective-mass approximation. The electronic properties are analytically studied on the basis of the effective-mass Hamiltonian for zinc-blende symmetry. The effective-mass parameters, such as crystal-field splitting, spin-orbit splitting, electronic effective mass,and the hole effective mass and the corresponding Luttinger-like parameters, are determined by reproducing the calculated band structures near the BZ center. The obtained results are in good agreement with available experimental and theoretical values.
2005, 54 (11): 5301-5307. doi: 10.7498/aps.54.5301
We have systematically studied the structural and electronic properties of MgS crystal by means of accurate first principle calculations. Our results show that this crystal has indirect band gap in the B1 structure and direct band gap in the B2,B3 and the B4 structures. Energy band width of the B2 structure is the smallest. When the pressure is below 200.3GPa, the B1 structure of MgS crystal is most stable. Above 200.3GPa this compound would undergo a structural phase transition from the relatively loose NaCl structure to the more dense CsCl atomic arrangement.
A first-principle study of electronic and geometrical structures of semiconducting β-FeSi2 with doping
2005, 54 (11): 5308-5313. doi: 10.7498/aps.54.5308
Firstly,the electronic structure of β-FeSi2 and the density of states (DOS) of subshells of Fe and Si were calculated. The calculations were carried out using the self-consistent full-potential linearized augmented plane wave method within the density functional theory. The general gradient approximation was used to treat the exchange and correlation potential. The DOS of β-FeSi2 is mainly composed of d-shell electrons of Fe and p-shell electrons of Si. Secondly,the stable atomic substitution positions of doping atoms were determined by calculating the total energies for Fe1-xCoxSi2 and Fe(Si1-xAlx)2. The Fe atom at the FeⅡ position and the Si atom at the SiⅠ position were preferentially substituted by Co and Al,respectively. This preferential substitution is in good agreement with results of the existing publications. Finally,the elctronic structures of Fe1-xCoxSi2 and Fe(Si1-xAlx)2 were calculated and analyzed as well. The intrinsic relations between electronic structures of Fe1-xCoxSi2 and Fe(Si1-xAlx)2 and their respective thermoelectric properties including Seebeck coefficient,electric conductivity and thermal conductivity were discussed in detail.
2005, 54 (11): 5314-5323. doi: 10.7498/aps.54.5314
A magnon-phonon interaction model is built in two-dimensional insulating ferromagnet. By using Matsubara Green function theory, we have studied the magnon damping -ImΣ*(1)(k), and calculated the magnon damping -ImΣ*(1)(k) curve on the main symmetric point and line in the Brillouin zone for different parameters of the system. It is concluded that at the boundary of Brillouin zone there is a strong magnon damping. But the magnon damping is very small on zones of small wave vectors, and magnon damping has maximal value at very low temperature. The influences of longitudinal phonon and transverse phonon on the magnon damping are compared, and the influences of the parameters are also illustrated. According to expression -ImΣ*(1)(k)=/(2τ), the magnon lifetime is discussed.
2005, 54 (11): 5324-5328. doi: 10.7498/aps.54.5324
The single excited state of a polaron in polymers has been studied. It was found that its polarization is negative under an external electric field. The single excited state of a polaron has a similar behavior with that of a biexciton. The inversed polarization will disappear under a strong electric field and the single excited state of a polaron will dissociate into a polaron and a bipolaron.
2005, 54 (11): 5329-5334. doi: 10.7498/aps.54.5329
Fe, Ni doped Ge-Sb-Se thin films are grown by electron-beam evaporation with targets sintered at low temperature, and show p-typed in conducting status. Investigated by AFM,UV-VIS,Hall and Impedance Analyzer, we observed that thin films have a more perfect network and less defects if the doped ion has a higher activity and smaller electronegative difference with the system elements, or the films are annealed. Fe and Ni doped in Ge-Sb-Se system not only take part in binding and affect the network perfection but also introduced defects near Fermi energy. Thin films doped with Ni have a more perfect network, lower neutron-hanging binding concentration and less polarons produced under AC electric field compared with Fe doped thin films, thus have smaller roughness, larger optical band gap, higher carrier mobility, lower carrier concentration and smaller dielectric loss.
2005, 54 (11): 5335-5338. doi: 10.7498/aps.54.5335
Within the effective mass approximation, the energy spectra of the donor- center quantum dot system in Gaussian confining potential are calculated by using the method of numerical matrix diagonalization. The results show that the property of the ground and low-lying states of the quantum dot is rather sensitive to the size and the strength of confinement potential.
According to the coupled-wave equations, the irregular properties at boundaries of the wave-guide with helical corrugation is analyzed using the method of impedonce perturbation. The general coupled equation of the helical wave-guide and the formuale for coupled coefficient are obtained. Based on rules of mode coupling in helical wave-guide, the dispersion equation is obtained and the dispersion characteristics are discussed.
Study of temperature dependent electroluminescence of InGaN/GaN multiple quantum wells using low temperature scanning near-field optical microscopy
2005, 54 (11): 5344-5349. doi: 10.7498/aps.54.5344
Though GaN based semiconductor materials and devices have achieved giant commerc ial success, there were few reports on their electroluminescent near-field optic al studies at low temperature. In this paper we present our results of the elect roluminescent near-field images and spectra at both room temperature and liquid nitrogen temperature by using a lab-made low temperature scanning near-field opt ical microscope. We found that with the decreasing of sample temperature, the fl uctuation of electroluminescent intensity in the near-field images is reduced gr eatly and the peak photon energy of the spectra emitted from the quantum wells e xhibits a blue-shift at first and then a red-shift. A new spectral peak emerges at higher photon energy at liquid nitrogen temperature. According to our analysi s, this higher photon energy peak is attributed to the transition from the botto m of conduction band to the acceptor energy states in the p-GaN cap layer.
Density functional theory study on the atomic structure and electronic states of Cu(100) (2×22)R45°-O surface
2005, 54 (11): 5350-5355. doi: 10.7498/aps.54.5350
The surface structure, relaxation, and oxygen adsorbed (2×22)R45° Cu(100) surf ace are studied by ab initio total energy calculation. The calculated atomic str ucture for the Cu(100) (2×22)R45°-O surface is quite close to the experiments except the positions of surface layer Cu atoms. The adsorbed O atoms is lying ap proximately 0.02 nm above the outermost Cu layer and produces a hybridized band and yields some localized surface states around 6.4 eV below EF. The calculated work function for studied oxygen adsorbed surface phase is 4.58 eV, w hich is close to that of clear Cu(100) surface (～4.53 eV). It is concluded that the bonding between adsorbate and substrate copper atoms is approximately limit ed to the first surface layer.
2005, 54 (11): 5356-5361. doi: 10.7498/aps.54.5356
The atomic structural models of the(100) and (110) surface of the Nix Cu1-x disordered binary alloy were set up when surface segregation is considered or not by computer programming.Then the models of the chemisorption of O on both surfaces were set up with the coverage θ=0.5. The electronic struc ture of O chemisorbed on the (100) and (110) surfaces of the NixCu1-x disordered binary alloy was calculated (considering and not consider ing the segregation).The calculated results show that (1) the chemisorption lowe rs the surface density of states of the disordered binary alloy,the energy band is widened, and the covalent bonds between the d electron of Ni and the s and p electron of O are stronger than that of Cu, (2) the O adsorbed on the (110) surf ace is more stable than on the (100) surface, and (3) the chemisorption of O on the surface restricts the surface segregation of Cu and this kind of influence i s obvious at the first layer.
2005, 54 (11): 5362-5366. doi: 10.7498/aps.54.5362
The structural stabilities and electronic structures of Nb atomic chains are studied by employing first-principles plane wave pseudopotential method based on the density functional theory. The calculations show that niobium can form planarchains in linear-, zigzag-, dimer- and ladder-form one-dimensional structures. The most stable one among the studied structures are the zigzag-form linear chain, and all the other structures are metastable. The relative structural stabilit y, the electronic energy bands, the density of states and the charge densities a re discussed based on the ab initio calculations and the Jahn-Teller effects.
Time-resolved photoluminescence of sub-monolayer InGaAs/GaAs quantum-dot-quantum-well heterostructures
2005, 54 (11): 5367-5371. doi: 10.7498/aps.54.5367
Time-resolved photoluminescence (PL) of sub-monolayer (SML) InGaAs/GaAs quantum-dot-quantum-well heterostructures was measured at 5 K for the first time. The radiative lifetime of SML quantum dots (QDs) increases from 500 ps to 800 ps with the increase of the size of QDs, which is related to the small confinement energy of the excitons inside SML QDs and the exciton transfer from smaller QDs to l arger ones through tunneling. The rise time of quantum-dot state PL signal stron gly depends on the excitation power density. At low excitation power density, th e rise time is about 35 ps, the mechanism of carrier capture is dominated by the emission of longitudinal-optical phonons. At high excitation power density, the rise time decreases as the excitation density increases, and Auger process pla ys an important role in the carrier capture. These results are very useful for u nderstanding the working properties of sub-monolayer quantum-dot devices.
2005, 54 (11): 5372-5376. doi: 10.7498/aps.54.5372
We have studied the thermal stability of magnetic tunnel junctions with and without nano-oxide layer (NOL) using x-ray hpotoelectron spectroscopy (XPS). The con centration and chemical states of elements,in particular Mn,have been obtained b y angel-resolved XPS and peak decomposition technique.It is confirmed that Mn in the antiferromagnetic layer can diffuse into the pinned ferromagnetic layer and the insulating barrier layer when a magnetic tunnel junction without NOL is ann ealed at high temperature.However,the interdiffusion of Mn during the annealing process is suppressed by inserting a NOL between the antiferromagnetic and pinne d ferromagnetic layer,and then the thermal stability is improved.
Performance of polymer light-emitting diodes with saturated red-emitting poly(fluorine-co-4,7-dithien-2-yl-2,1,3-benzothiadiazole-carbazole or triphenylamine)
2005, 54 (11): 5377-5381. doi: 10.7498/aps.54.5377
Since electron or hole injection is a limiting factor for most electroluminescen t polymers, a matching of the work function of cathodes and anodes and the LUMO ＼HOMO energy level of polymers is one of the important factors for high perform ance polymer light emitting devices. In this paper, we report the effect of the cathodes on the performance of the device based on saturated red emitter, three- component copolymer poly (fluorine-co-4, 7-dithien-2-yl-2, 1,3-benzothiadiazole- carbazole or triphenylamine) copolymers. By thermal deposition in combination wi th spin-coating of electron injection layer, we investigated the influence of va rious cathode meterials with different ionization potentials in order to optimiz e the balance of the electron and hole injection. The external quantum efficien cy reached 1.49% with luminance 466cd/m2，the EL spectrum peak is loc ated at 657nm with the color coordinate: x=0.69, y=0.30 for PFO-5Cz-15DBT.
2005, 54 (11): 5382-5388. doi: 10.7498/aps.54.5382
The Gd substituted Y1-xGdxBa2Cu3O7-δ systems are studied systematically by positron annihilation and x-r ay diffraction. The x-ray results show that the crystal parameters and crystal v olume of the systems increase with the increase of Gd content. However, all the substituted samples maintain the single orthorhombic phase as YBa2Cu3O7-δ (YBCO) sample does. The positron annihilation result s show that positron lifetimes depend on the Gd content strongly. According to t he positron annihilation result, the local electronic density on Cu-O chain is c alculated. The result shows the local electronic density decreases with the incr ease of the Gd content, while the Tc increases with the decrease of t he local electronic density. The relationship between the local electronic densi ty and superconductivity is different from the substitution on Cu site, which ma y be one of the reasons why the mixed rare earth cuprate superconductor has a hi gher critical electric current density than the YBCO. These experimental results give the corresponding positron experiment data for the application of cuprate superconductors and study of the mechanism.
2005, 54 (11): 5389-5394. doi: 10.7498/aps.54.5389
The(Ni79Fe21)1-xNbx(5nm)/(Ni79Fe21) (20nm)/Ta(3nm) films are prepared with the (Ni79Fe21)1-xNbx seed layers. The grain size, hyste resis loops and surface roughness of samples are measured and the variations of hysteresis loops with the Nb atomic concentration in the seed layers are analyze d. The results show the microstructure of the permalloy films grown on the seed layers is improved. The coercivity and the (B·H)m in the hysteresis loop is minimal at x=23%. The influence of seed layers on the hysteresis loops is partly duc to the different excitation energy of different seed layers, which result in different roughness of the surface of the seed layers film, hence the different microstructure of the permalloy films.
2005, 54 (11): 5395-5399. doi: 10.7498/aps.54.5395
CoPt/Ag nanocomposite films were prepared by magnetron sputtering. The dependenc e of texture and magnetic properties on film thickness, bilayer thickness, Ag at omic fraction and annealing conditions is investigated. Films with thickness bel ow 20 nm are apt to form (001) orientation. The existence of the Ag in the film plays a dominant role in inducing the (001) texture of the film besiles suppress ing the growth of the CoPt grains during annealing. The Co40Pt43 Ag17 film after annealing at 600℃ exhibits a large perpendicul ar coercivity of HC=5.6×105 A/m, a large saturation magne tization of MS=0.65T and a squareness of s=0.95 of the hysteresis loo p.
2005, 54 (11): 5400-5404. doi: 10.7498/aps.54.5400
In the sintered Nd-Fe-B magnets, the forming of various phases, substitution and preference of additive atoms, microstructure and properties, and, most of proce ssing have a close relationship to the thermodynamics. The Al, Cu, Ga, Sn, Zn ha ve positive heat of mixing with the B, the solubility of them in the main phase is small, they react with Nd in the grain boundary and modifying the microstruct ure of the magnets. The Zr, Ti, Nb, W, Mo, V, Cr have large positive heat of mix ing with Nd while have large negative heat of mixing with the B, they can modify the microstructure as well as dilute the magnets. The effects of the common add itional elements on the microstructure, properties and the processes of Nd-Fe-B magnets are discussed in this work by referring the heat of mixing and the binar y diagrams.
2005, 54 (11): 5405-5410. doi: 10.7498/aps.54.5405
We have grown epitaxial Co films on a single monolayer of Pd on Cu(100) substrate at room temperature. The interlayer of Pd was grown by pulsed laser deposition, whereas the Co layer was prepared by thermal deposition. A layer-by-layer growth mode continues until at least 11 ML Co layers in comparison to 4 ML on Pd(100)substrate, which is due to a reduced lattice mismatch between Co and the Pd/Cu(100) substrate in comparison to the Co on Pd(100) system. Compared to Co films on Pd(100), a larger slope of the thickness dependence of longitudinal magneto-o ptical Kerr rotation has been found in the Co/Pd/Cu(100) films with thickness ab ove 2 ML. We have also found an increase of longitudinal magneto-optical Kerr ro tation for Co/Pd/Cu(100) in comparison to Co/Cu(100) system which may be attribu ted to the Co/Pd interface effect.
2005, 54 (11): 5411-5416. doi: 10.7498/aps.54.5411
PST thin film doped with Mg was successfully prepared using sol-gel process. The phase structure of the thin film was measured by XRD and the morphology of microstructure of the thin film was observed by SEM. Results showed that the cubic perovskite phase is formed in Mg-doped Pb0.4Sr0.6MgxTi1-xO3-x thin film prepared by sol gel process. The clustered crystallites are distributed and embedded in the base matrix of thin f ilm. However, the contents of the perovskite phase was controlled by both Mg dop ing and heat treatment condition due to formation of intrinsic oxygen vacancy in the perovskite phase. The charge balance between the positive from the intrinsi c oxygen vacancy and the negative from Mg substitution for Ti occurs when small amount of Mg is doped in the perovskite phase. The stable perovskite phase forms easily, and the crystallization of the perovskite phase is hence increased with increasing Mg doping up to x=0.01. The distortion of the perovskite phase struc ture would increase with farther increase of Mg doping in the crystallites above about x=0.01 due to the generation of a lot of oxygen vacancies. Henceforth uns table perovskite phase is formed and the crystallization of the film decreases w ith increasing Mg. Thus highest content of the perovskite phase is reached and t he charge balance between positive and negative occurs in the film when Mg dopin g is x=0.01. Furthermore, the formed crystalline phase may decompose with increa sing Mg content and time of heat treatment. So in the case of high Mg doping the higher the content of Mg and the longer the time of heat treatment, the lower t he content of perovskite phase is contained in the film.
2005, 54 (11): 5417-5421. doi: 10.7498/aps.54.5417
Carbon-doped oxide materials (SiCOH films) with k of 2.45 and good thermal stability at temperature 485℃ are prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) from the mixture of decamethylcyclopentasioxane (D5, ［Si(CH3)2O］5) and methane (CH4). T he chemical structures of D5 as a liquid source and films deposited with differe nt methane flux are studied by Fourier transform infrared spectroscopy. The resu lts indicate that the increase of methane is of great advantage to the reservati on of ring structure of D5 as well as the formation of high density CHn fragments in films. The decrease of dielectric constant is induced by the com bined action of several factors: lower density of films caused by high density o f CHn fragments and formation of intrinsic pores, lower polarization caused by the formation of Si-C bond and decrease of-OH bonds.
2005, 54 (11): 5422-5427. doi: 10.7498/aps.54.5422
Ferroelectric Sr2Bi4-xDyxTi5O18 (SBDT-x, x= 0—0.20) ceramic samples were prepared using the conventional solid-state reaction method. x-ray diffraction patterns (XRD) of SBDT-x ceramics show that doping with a small amount of Dy does not change the crystal structur e of Sr2Bi4Ti5O18 (SBTi). Their Curi e temperature (Tc) and dielectric loss (tanδ) decrease with Dy dopin g amount. The remnant polarization (2Pr) of SBDT-x increases at first , then decreases with increasing of Dy content. When Dy content is 0.01, the 2Pr reaches a maximum value of 20.1 μC·cm-2. The variation of 2Pr for SBDT-x relates to space charge density, internal strain an d structure distortion. (Bi2O2)2+ layer acting as an insulating layer and space charge storage plays an important role in their ferroelectric properties in BLSFs. The incorporation of doping ions into (Bi2O2)2+ layer may destroy its original function and deteriorate the ferroelectric property.
Photorefractive gain property and optimization of dynamic holographic gratings in arbitrarily cut sillenite crystal
2005, 54 (11): 5428-5434. doi: 10.7498/aps.54.5428
We study the influence of vectorial wave coupling on the wave eigenmodes in an arbitrarily-cut photorefractive and optically active piezo-electric sillenite cry stal, and solve the vectorial equations for weak two-wave coupling. We deal exac tly with the vectorial wave coupling in an optically inactive piezo-electric cry stal by solving the scalar equations. By doing so we calculate the signal gains in the optically active and the optically inactive crystals and discuss the cont ributions of the isotropic and the anisotropic coupling to the gain, respectivel y. We optimize the signal gain of the optically active crystal and apply the re sults to a BSO and BTO crystal. We also investigate the influence of the piezo-e lectric and elasto-optic effect on the optimum gain for (110),(111),(112) and th eir equivalent cuts.
2005, 54 (11): 5435-5444. doi: 10.7498/aps.54.5435
Although the classical and quantum theories of Raman scattering of light by optical phonons have been well established, the papers genarally emphasized on some particular aspects of the scattering. For this reason, we need to develop a gene ral quantum theory of Raman scattering, taking account of both nonpolar and pola r modes. In our quantum theory, Raman scattering of light by longitudinal and tr ansverse polar modes can be described within a unified theoretical framework.
2005, 54 (11): 5445-5449. doi: 10.7498/aps.54.5445
Spectral properties of transparent polycrystalline Cr3+:Al2O3 ceramics were studied. The results indicated that the absorption peaks of polycrystalline Cr3+:Al2O3 ceramics co incide with the absorption spectrum of a ruby single crystal. The crystal field and Racah parameters were calculated according to the Tanabe-Sugano energy level diagram and absorption spectra. The crystal field intensity of Cr3+: Al2O3 polycrystalline ceramics is almost the same as that of Cr3+:Al2O3 single crystal, and the character istics of the emission spectra still retains the R-line emission even as the Cr3+ concentration increases up to 0.8wt%. In particular, one 670nm emis sion peak of Cr3+ was first found in the polycrystalline ceramics.
2005, 54 (11): 5450-5454. doi: 10.7498/aps.54.5450
GaN epitaxial films were grown on c-face sapphire substrates by metalorganic chemical vapor deposition (MOCVD) with an in situ SiNx deposition insert ed into the normal growth process. The in situ SiNx deposition makes a nanomask on GaN, followed by the epitaxial lateral overgrowth on it. Raman spe ctra and photoluminescence are used to study the stress state of the resulting G aN film. The formation of SiNx nanomask leads to a 2D-3D growth mode transition, which ends in the total coalesce of the GaN film. The distribution o f stress state in this kind of GaN film is more uniform than that of films grown by the conventional epitaxial lateral overgrowth. The data about the relaxation of the stress deduced by the Raman spectra match well with those obtained by ph otoluminescence. These data also show that the more residual stress in the GaN f ilm grown on the SiNx nanomask is relaxed when the time of in situ Si Nx deposition is increased. This is because with the increasing time of in situ SiNx deposition, the wing area of epitaxial lateral overgr owth becomes larger, which will reduce the stress in the GaN thin film grown on it.
2005, 54 (11): 5455-5461. doi: 10.7498/aps.54.5455
The fluorescence spectra of the ethanol-water mixture excited by ultraviolet lig ht and the excitation spectra corresponding to the fluorescence peaks are inves tigated respectively. It is found that the mixtures emit fluorescence photons, which is different from pure ethanol and water. One can conclude that new molec ule clusters are created by mixing of the ethanol and water molecules. The inci dent light of different wavelengths irradiates the solution and the fluorescen ce quantum yield at each wavelength is calculated firstly, and then the excited light with the maximum quantum yield is selected to irradiate the mixture. By the experimental results of fluorescence spectra of solution with different con centrations, the possible structures of these new molecule clusters are discuss ed. The general absorptivity and fluorescence counts are calculated basing on t he additive property of absorptivity and fluorescence intensity, elucidating the fluorescence spectra characteristic of ethanol-water mixture. The research may contribute to the study of the new molecule clusters of ethanol-water.
2005, 54 (11): 5462-5467. doi: 10.7498/aps.54.5462
Er/Yb co-doped soda-silicate glasses with 0.5 at.% Er and various concentrations Yb were fabricated. The absorption and the photoluminescence (PL) spectra were measured and analyzed. The PL intensity of the Er/Yb co-doped soda-silicate glasses is enhanced 4 times approximately, and the optimum Yb concentration for the PL intensity at 1536 nm is 3.0 at.%. The PL spectrum becomes broader with the in crease of Yb concentration, up to a FWHM of 80 nm at 6.0 at.% Yb. The relation b etween absorption and PL spectra, together with the mechanism of PL broadening, has been addressed.
2005, 54 (11): 5468-5473. doi: 10.7498/aps.54.5468
Yttrium aluminum garnet (YAG): Pr3+ is synthesized by codeposition me thod. Vacuum ultraviolet (VUV) excitation and emission spectra of YAG: Pr3+ at different temperatures are measured using synchrotron radiation as an excitation source. We analyze the transition process after excitation to 4f5d en ergy band and estimate the Huang-Rhys factor S and phonon energy ηω of YAG: Pr 3+ by multi-phonon relaxation. Emission of self-trapped exciton (STE) and 3P0→3H4,5,6 emission transferr ed from the STE energy appear when YAG: Pr3+is excited by 170nm, whic h is a different transition process from those excited by 240nm and 289nm.
Research on the effects of thickness of cobalt layers on the orbital and spin moments of Co atoms using x-ray magnetic circular dichroism in absorption
2005, 54 (11): 5474-5480. doi: 10.7498/aps.54.5474
Orbital and spin moments of Co atoms in films of different thickness deposited by magnetron-sputtering on silicon wafers have been investigated by use of soft x -ray magnetic circular dichroism in absorption. Layers with thickness 2nm, 10nm and 30nm are covered by 0.8—1nm of protection overlayer. Orbital and spin momen ts of 0.249—0.195μB and 1.230—1.734μB are found from X MCD sum rules. Increase in orbital moments and decrease in spin moments are obse rved with reducing cobalt film thickness. There is a ratio variation from 0.101 to 0.168 of orbital moment to total moment, that is, contribution of orbital mom ent of cobalt atoms to total moment in 2nm film is 83% greater than that in the 30nm film.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2005, 54 (11): 5481-5486. doi: 10.7498/aps.54.5481
The single-phase dual-atom filled p-type CamCenFexCo4-xSb12 compounds were synthesized by melting reactio n method. Effects of Ca and Ce filling fraction on the thermoelectric properties of the p-type CamCenFexCo4-xSb 12 were investigated. Our results indicate that with the same filling frac tion, carrier concentration and electrical conductivity of p-type Cam CenFexCo4-xSb12 intervene between t hat of single atom filled compounds CamFexCo4-x Sb12 and CenFexCo4-xSb12, and decreased with increasing Ca and Ce, especially Ce, filling fraction. With the same filling fraction, the lattice thermal conductivity of CamCenFexCo4-xSb12 is smaller than that of CamFexCo4-xSb12 and CenF exCo4-xSb12. Furthermore, when the total fillin g fraction (m+n) is about 0.3 and the filling fractions of Ca and Ce are approxi mately equal, the lattice thermal conductivity is the smallest. The greatest ZT value of 1.17 was obtained at 750K for p-type Ca0.18Ce0.12 Fe1.45Co2.55Sb12.21.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2005, 54 (11): 5487-5493. doi: 10.7498/aps.54.5487
Global change science is a new research domain nowadays, and one of the most imp ortant studies of which is the climate change,to which great attention is paid b y all governments in world. It is mainly based on the climatic proxy that we can study the past climate change. Although many achievements have been obtained, m ajority of the results are limited to the external characteristics of the proxy due to lagged analysis methods. For example, we judge if the climate is flood / drought or cold/warm through linear trend of the time series, however, we do not know whether it is a natural variation or the result of external forces, the me chanism is not uncovered. Because complexity of the open global climate system, there are different characteristics among the climatic proxies from different re gion of the world, from which it is difficult to reveal the intrinsic general pr inciples i.e. the globality. For the further study on the past climate change, e specially to reveal the rulcs of the global climate change in past 2000a and pre dict future climate change, a new method making use of the dynamical lag correla tion exponent (named Q index in the text), a dynamics exponent based on the phas e-space reconstruction, is introduced in this paper, which can effectively disce rn the similarities or differences between the dynamics of the two series. With Q index, we analyze the dynamics structure of some typical climatic proxies. The results show that the dynamics of climatic proxies are almost similar, and the regional climate keeps the same change with the global. In other words, regional climate is controlled by the global climate change. Besides, there are two dyna mics jump periods (namely 700—900a and 1300—1700a) in past 2000a of the climat e system, which may correspond to the periods of the medieval warm period and th e little ice age, respectively.
2005, 54 (11): 5494-5499. doi: 10.7498/aps.54.5494
Climate system is nonlinear,non-stationary and hierarchical,which makes even harder to detect and analyze abrupt climate changes.Based on Student's t-test,Berna ola Galvan recently proposed a heuristic segmentation algorithm to segment the t ime series into several subsets with different scales,which is more effective in detecting the abrupt changes of nonlinear time series.In this paper,we try to v erify the effectiveness of heuristic segmentation algorithm in dealing with nonl inear time series by an ideal time series.Through detecting and analyzing the in formation of abrupt climate changes contained in recent 2000a's tree annual grow th ring,we succeeded in distinguishing abrupt changes with different scales.The research based on the newly defined paramcter of abrupt change density shows tha t human activities might have lead to the recent 1000a's unbalanced distribution of serial and spares segments of abrupt climate changes,which may be one of the manifestations of global temperature change.
2005, 54 (11): 5500-5503. doi: 10.7498/aps.54.5500
The contribution of gravitational field of spin 2 to the entropy of Vaidya-Bonne r black hole is calculated by using thin film brick-wall model proposed by Zhao Zheng et al., which is found to be A/2 in nature unit system. It is shown to be just two times the scalar field and 4/7 times the Dirac field when the truncatio n factor is the same as scalar fields.
2005, 54 (11): 5504-5510. doi: 10.7498/aps.54.5504
The microcanonical statistics of the Kerr black holes is analyzed. We have set u p an inequality in the microcanonical density for both continuous spectrum and d iscrete spectrum, and have verified that Kerr black holes obey the statistical b ootstrap condition. It is then used to show that the most probable configuration in the gases of Kerr black holes is that one black hole acquires all of the mas s and all of the rotation at the high-energy limit, so rotation does not break t he bootstrap property.