Vol. 54, No. 3 (2005)
2005-02-05
GENERAL
2005, 54 (3): 993-995.
doi:10.7498/aps.54.993
Abstract +
A class of coupled systems in oscillation of the El Nio-Southern Oscillation (ENSO) mechanism has been studied. Using the homotopic mapping and perturbed theory, approximate expansions of the solution for a class of ENSO model are obtained in a simple manner.
2005, 54 (3): 996-1001.
doi:10.7498/aps.54.996
Abstract +
In this paper, by using the technique of generalized Lie group reduction, the exact solutions of the nonlinear Schrdinger equation with distributed dispersion, nonlinearity, and gain (or loss) are obtained. And, the potential application of the general solitary wave solutions and the chirped solitary wave solutions in optical fibers communication and optical fibers amplifiers have also been studied thoroughly. This will provide the possibility in making new optical fibers amplifiers.
2005, 54 (3): 1002-1008.
doi:10.7498/aps.54.1002
Abstract +
With the aid of computer symbolic systems Maple, and by an improved algebraic method which is used to construct a series of more general exact solutions to nonlinear differential equation or coupled equations, we have solved the (2+1)-dimensional Broer-Kau-Kupershmidt equation, and obtained a number of new exact solutions including polynomial solutions,exponential solutions, rational solutions, triangular periodic solutions,hyperbolic solutions, and Jacobi and Weierstrass doubly periodic wave solutions.
2005, 54 (3): 1009-1014.
doi:10.7498/aps.54.1009
Abstract +
A Hojman conserved quantity constructed by using the special Lie symmetry, or the Noether symmetry, or the form invariance for a holonomic system in the event space is studied. First, the differential equations of motion of the system are established. Second, the critera of three kinds of symmetries, such as the Lie symmetry, the Noether symmetry and the form invariance, and the relation among them are obtained. Third, the conservation law theorem gained by Hojman is generalized and applied to the system, and a non-Noether conserved quantity is obtained. Two examples are finally given to illustrate the application of the results.
2005, 54 (3): 1015-1017.
doi:10.7498/aps.54.1015
Abstract +
The motion of a charged particle in an electromagnetic field is studied by Mei symmetry.Based on the Mei symmetry of two-dimensional particle motion, the generator and the partial differential equations for the electromagnetic field are obtained by comparing the coefficients of all the monomials. A specific example is given in this paper.
2005, 54 (3): 1018-1035.
doi:10.7498/aps.54.1018
Abstract +
The scattering of ultrashort and ultraintensie laser pulses by single electrons has been investigated theoretically and numerically by use of the classical theory of Thomson scattering by free electrons. The results indicate that attosecond pulse trains are emitted during the interaction. The temporal and spatial characteristics of the radiation are presented for different laser parameters(including intensity, pulse duration, initial phases and polarizations) and initial states of the electron(including different initial velocities and positions). Usually, with the increase of the incident laser intensity, the radiation becomes more powerful, its central frequency becomes higher, its duration becomes shorter, and its angular distribution becomes smaller. The radiation produced by the electron under a linearly polarized laser has a higher amplitude than under a circularly polarized laser pulse with the same intensity. In both cases, the polarization state of the radiation is very complicated, which depends n the observation direction. In spite of its initial energy and moving direction, the radiation produced by relativistic energetic electrons tends to be predominantly along the moving direction of the electron.
2005, 54 (3): 1036-1038.
doi:10.7498/aps.54.1036
Abstract +
By using a transformation we introduced formerly, a nonlinear partial differential equation can be reduced to a nonlinear ordinary differential equation, and then solve it directly. And the exact analytical solutions to the Burgers equation can be easily derived. The results obtained in this paper is in good agreement with those given in the literature.
2005, 54 (3): 1039-1043.
doi:10.7498/aps.54.1039
Abstract +
By using a functiontransformation method, coupled KleinGordornSchrdinger equations are reduced to the integrals that can be solved with elementary functions and elliptic functions. Its exact solutions that include discontinuous solutions, hyperbolic function type solutions and elliptic function type solutions, and a special solutions obtained in a reference, are given.
2005, 54 (3): 1044-1047.
doi:10.7498/aps.54.1044
Abstract +
A rigorous solution of Schrdinger equation of an spheresymmetry harmonic oscillator is studied by the power series method.We found that wave function ψ(r,θ,φ)|r～0 can be infinite, rψ(r,θ,φ)|r～0 must be finite; this is in accord with Born's statistical explanation. The groundstate energy of the spheresymmetry harmonic oscillator is ω/2. The space dent will appear in the ground state of the spheresymmetry harmonic oscillator.
2005, 54 (3): 1048-1052.
doi:10.7498/aps.54.1048
Abstract +
The nonadiabatic conditional geometric phase gate is required in the topological quantum computation in order to overcome the conflict between the requirement of adiabatic condition(to avoid the severe distortion from the nonadiabaticity to the results) and the removal of decoherence effects. It was demonstrated that the effective Hamiltonian that describes the propagation of photon fields inside the coiled fiber is just the WangMatsumoto type of Hamiltonian. Thus, the coiled fiber system will automatically generate the nonadiabatic conditional geometric phase shift. In addition, it was shown that the dynamical phase(resulting from the effective Hamiltonian) acquired by the polarized photons vanishes, and the conditional initial state can be easily prepared only by controlling the initial wave vector of photons. In a word, the coiled fiber system can automatically satisfy the requirements and conditions, which were proposed by Wang and Matsumoto in order to create the nonadiabatic conditional geometric phase shift in their NMR scheme.
2005, 54 (3): 1053-1058.
doi:10.7498/aps.54.1053
Abstract +
The coherently coupled nonlinear Schrdinger equation of the propagation of a light pulse in a nonlinear birefringence fiber has been utilized.We have studied modulation instability not only in an anomalous dispersion regime but also in a normal dispersion regime when the angle between the polarized direction and the birefringence axes is arbitrary.The results show that the instability polarized region and stability polarized region exist not only in the anomalous dispersion regime but also in the normal dispersion regime. The input pulses have obviously different gain spectra when the instability polarized region and input different power are different.
2005, 54 (3): 1059-1063.
doi:10.7498/aps.54.1059
Abstract +
This paper studies the detection of the nonlinearity of time series sampled from continuous dynamics systems by using the surrogate data method. The results show that under the different sampling conditions, the detection finds different nonlinearity of chaotic time series. Especially for the oversampling time series, there can often be some illusive results. For this, we suggest that it is best to apply nonlinear values as testing statistics for detecting nonlinearity of oversampling time series.
2005, 54 (3): 1064-1070.
doi:10.7498/aps.54.1064
Abstract +
For a coupled nonlinear oscillator system with diffusion and gradient couplings, spatial Fourier transformation is performed and the dynamic equations of various space modes are derived. By calculating the Lyapunov exponents of the transverse modes, one can determine the stable region of the synchronous chaos on the plane of coupling parameters. On the boundary of the stable region, a couple of conjugate transverse modes destabilize, and a Hopf bifurcation takes place. Numerical simulations are carried out for the coupled Lorenz oscillator system. An electronic circuit is designed for simulating the bifurcation in the system. Results from the simulations show that the frequency created by the Hopf bifurcation is equal to the oscillation frequency of the destabilized transverse modes.
2005, 54 (3): 1071-1080.
doi:10.7498/aps.54.1071
Abstract +
This article reports a characteristic crisis observed in a kicked rotor subjected to a piecewise continuous force field. The discontinuity border in the definition range of the twodimensional mapping, which describes the system, oscillates as the discrete time develops so that the forward images of the border form a fat fractal. With a chosen group of parameters the iterations on the fat fractal display chaotic motion, and the transient iterations from the initial values in a certain region of the phase space are attracted to the fat fractal. At a threshold of a control parameter, an elliptic periodic orbit suddenly appears inside the fat strange set, inducing an escaping of the iterations to the elliptic islands around it. The fat chaotic attractor thus suddenly transfers to a fat transient set. The influence of the feature of the crisis on the dependence of the lifetime in the transient set on the control parameter has been analyzed. It is shown that the dependence follows a universal scaling law suggested by Grebogy, Ott and Yorke, and the scaling exponent can be approximated according to the variation rules of the elliptic islands and the measure of the fat fractal as control parameter changes. It is possible to compare the results of the direct numerical computation on the scaling exponent and that obtained with the approximation. They are in good agreement.
2005, 54 (3): 1081-1083.
doi:10.7498/aps.54.1081
Abstract +
The El Nio atmospheric physics mechanism is studied. Using the variational iteration theory, the approximation of the solution for its model is obtained for shortcut calculation. And compared to the special case for the exact solution of the model, the first approximate solution from the variational iteration method is in excellent agreement with the exact solution in degree of accuracy.
2005, 54 (3): 1084-1091.
doi:10.7498/aps.54.1084
Abstract +
Based on the sequence of circuit topologies, a symbolic sequence method is proposed for analyzing the bifurcations and chaos in a class of piecewise smooth systems like DC/DC converters. The largest subsequence(LS) is used to distinguish the type of bifurcation and detect border collision bifurcation e. g., when a perioddoubling bifurcation occurs, the LS is unchanged; when border collision bifurcation occurs, the LS is changed; and when chaos occurs,the LS does not exist.It is shown that the duty ratio is an essential variable for describing the nonlinear dynamics of a class of piecewise smooth systems like DC/DC converters， and saturating nonlinearity is the root cause of border collision bifurcation.
2005, 54 (3): 1092-1097.
doi:10.7498/aps.54.1092
Abstract +
The conventional variable structure control(VSC) methods for controlling chaos have some drawbacks, such as high_frequency chattering and the need of a prior knowledge about the upper bound of the uncertainty. Trying to solve the drawbacks, we proposed an adaptive chatteringfree variable structure control(ACFVSC) method for controlling a class of uncertain timevariable chaotic systems towards arbitrarily desired trajectory. The ACFVSC method not only eliminates the chattering phenomenon and tracks arbitrarily desired trajectory asymptotically, but also removes the prior knowledge about the upper bound of uncertainty. Both the asymptotic tracking analysis of ACFVSC and simulation results show that the arbitrarily desired tracking accuracy can be achieved within a finite time if the parameter of ACFVSC controller is appropriately set.
2005, 54 (3): 1098-1104.
doi:10.7498/aps.54.1098
Abstract +
In this paper, the control of chaotic externalinjection multiplequantumwell laser synchronization via phasecontrollers is presented and external chaos phase shift keying modulation is proposed for secure communication. Chaotic laser synchronization is numerically achieved under controlling by phasecontrollers. Lasing phase shift is controlled via continuous ON/ON chaos shift keying and chaotic laser signal is transmitted by chaos phase shift keying modulation on end. Chaotic laser demodulation is realized by setting a phase shift of the receiver phasecontrollers. ON/ON chaos phase shift keying communications at bit rates of 01 and 05Gbit/s are numerically simulated. ON/ON chaos phase shift keying communication bit rate，the synchronization characterization and the system parameter mismatch are numerically analyzed, in particular.
2005, 54 (3): 1105-1112.
doi:10.7498/aps.54.1105
Abstract +
The numerical path integration based on GaussLegendre scheme is extended to the case of nonlinear dynamical system under stochastic parametric and external excitations. For the purpose of comparison between the numerical solutions and the analytic solution(if the system has) or MonteCarlo simulation, we discuss the system under parametric and external Gaussian white noise excitations. The numerical method is shown to give accurate results. Via the numerical solutions of path integration, we have studied the P bifurcation of the stochastic system.
2005, 54 (3): 1113-1117.
doi:10.7498/aps.54.1113
Abstract +
Anomalous diffusion happens often in nature and society systems. In this paper, we develop a nonlocal method with temporal and spatial correlations to introduce a fractional order advectiondiffusion equation based on the usually used local 2_nd order advectiondispersion equation. In this equation, the diffusion is a fractional order derivative of time and space. And then, we extend the classical Fick's law for standard diffusion to a general fractional Fick's law. The fractional Fick's law shows that the current is related to the concentrations all over the space, also depends on the previous history and the initial condition. The solution of this fractional order advectiondispersion equation is fractional Lévy probability distribution density. And the mean square displacement is a nonlinear function of time.
2005, 54 (3): 1118-1125.
doi:10.7498/aps.54.1118
Abstract +
The stochastic resonance(SR) characteristics of two bistable systems connected in series have been investigated. It is deduced that the first bistable system of the cascaded system is most important because of its converting a white noise into a color one, and the subsequent bistable systems continuously concentrate noise energy into lowfrequency area in terms of Lorentzian distribution, which weakens the highfrequency dithering of the last output waveform and outlines the basic shape of the wave. The law of the signal spectral amplitude varying with noise intensity indicates that within a limited lowfrequency band, the cascaded system is able to promote the height of the signal spectral spike by a certain amount of noise. If the former of the cascaded system does not stay in SR, the latter could not optimize the former output to become a SR state. With the increase of the number of the bistable systems in the cascaded system, the lowfrequency area where most of the noise energy is collected will be narrowed gradually, and hence the signal peak is easily reduced and submerged in noise. For this case, in spite of using the twice-sampling technique to improve the signal spectral spike, the improvement is limited. Therefore, a single bistable system is effective for signal detection.
2005, 54 (3): 1126-1131.
doi:10.7498/aps.54.1126
Abstract +
The Bi_Mn wt6% alloys were solidified from semi_solid state in a magnetic field. The microstructure and magnetic properties have been studied systematically. The results show that the samples were of a eutectic structure of double phases and have large anisotropy. It was shown that the alignment of MnBi crystals occurred along the induced field. With increasing induced magnetic field, the remanence(Mr) increased gradually, which shows that the higher the induced magnetic field, the better the alignment. The spin reorientation temperature (TSR) for MnBi alloys increases with increasing induced magnetic field. The effects of the induced field on the microstructure and the magnetic properties of Bi_Mn wt6% alloys were also discussed.
2005, 54 (3): 1132-1135.
doi:10.7498/aps.54.1132
Abstract +
The principle for neutron phase contrast and tomography is presented in this paper.The imaging method for neutron phase_contrast tomography is suggested.It has the merits of both neutron phase contrast and tomography.The 3D space distribution for phase objects can be reconstructed with high resolution without using interferometry.The objective space structure with near absorption coefficient can be detected and resolved.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2005, 54 (3): 1136-1141.
doi:10.7498/aps.54.1136
Abstract +
The mass spectra of heavy quarkonia are calculated with the relativistic quark model.The effective interaction between a quark and an antiquark of the same flavor is assumed to be the sum of the one_gluon exchange with the inclusion of annihilation terms and the mixture of scalar and vector linear confining potentials with the relativisic corrections.The effects of the annihilation and the relativistic correction terms on the hyperfine splittings of quarkonium states are discussed in detail,and a good fit to the observed experimental data is obtained on the mass spectra.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (3): 1142-1148.
doi:10.7498/aps.54.1142
Abstract +
By using the accurate inequalities of the electron density at the nucleus and radial expectation values for atomic systems derived by Gálvez and Porras, we separately construct two sets of precise criterion of the wave function, they are another precise criterion independent of energy to test quality of the wave function. In this paper, we use the excited states of lithiumlike systems as research objects and examine the upper bound of the electron density at the nucleus and radial expectation value for the lithiumlike systems 1s23s state, R6 defined by the upper bounds of the electron density at the nucleus and R4 defined by the upper bounds of radial expectation value for the lithium atom 1s23s state in different calculation methods are also tested，at the same time we check up the upper bound of the electron density at the nucleus and radial expectation value for double excited states of the lithium atom. Research has shown that these two sets of inequalities can be used as precise criterion for wave function of energy states of atomic systems.
2005, 54 (3): 1149-1155.
doi:10.7498/aps.54.1149
Abstract +
A new expression for photoionization cross section has been proposed based on the Beer_Lambert's law and Maxwell equations for a material.And we also proposed a function varying with the number density of the system,which includes the local field effect and the higher_order dielectric correction to the famous formula for photoionization cross section of isolated atoms,proposed by Fano and Cooper in 1968The photoionization cross sections of solid xenon have been studied by using this alternative expression which couples the macroproperty and the quantum quantity of the photoionization system,and which makes it possible for one to study the influence of induced dipoles on the photoionization.The dielectric behaviors of the matter in condensed state under several physical conditions (given the complex dielectric constants or the model of electric susceptibility of the system) are considered using our new expression for photoionization cross sections.The results show that it is reasonable in physics to calculate the cross sections of atoms in a real system by using the accurate expression.Furthermore,the more correct the model of electric susceptibility for the real system,the more accurate the cross section obtained from our formula will be.
2005, 54 (3): 1156-1161.
doi:10.7498/aps.54.1156
Abstract +
The statistical properties of the system consisting of a trapped ion and a single_mode quantized radiation field are investigated under the conditions of carrier excitation (ωL=ω0), red excitation ［ωL=ω０-jν(j=1,2,3)］ and blue excitation ［ωL=ω０+jν(j=1,2,3)］.The time_evolution of the state of the system,the photon_and phonon_state exchange conditions and the corresponding populations of the ion are discussed.The corresponding averages and variances for photon and phonon numbers,as well as the second_order correlation function for the photon and phonon fields etc,have been obtained.
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (3): 1162-1166.
doi:10.7498/aps.54.1162
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The effect of different optical magnifications on the amplitude and linearity of displacement signals measured by the photodiode quadrant detector in an optical tweezers system is studied both experimentally and theoretically. Based on the experimental results we find that the output signal with larger amplitude and more preferable linearity can be obtained when the magnified images of α particle have diameters of 50% to 60% of the detector diameter. Theoretical calculation confirms it.
2005, 54 (3): 1167-1171.
doi:10.7498/aps.54.1167
Abstract +
A new asymmetrical pulse pair method is proposed which can be used to suppress the pulse walk_off effect during the process of pulse compression by the cross phase modulation of pulse pair. By using asymmetrical pulse pair method and asynchronous coupling method, the suppressions of the walk_off effect have been investigated numerically. Results show that for an incident Gaussian pulse with peak power 10mW and full_width_at_half_maximum (FWHM) 5ps, we can obtain a compressed pulse with the compression factor 137, pedestal energy ratio 0122 and the peak power 116mW by adopting the asymmetrical pulse pair method.
2005, 54 (3): 1172-1177.
doi:10.7498/aps.54.1172
Abstract +
The inside source hologram reconstruction algorithm based on discrete Fourier transform was investigated in detail, and how to calculate the contribution of whole spherical hologram to the reconstructed image of atoms was demonstrated in this algorithm, which was previously regarded to be capable of calculating only half of the spherical hologram. Using the sampling theorem in this issue, we are able to examine such essential factors as the sampling rate of the hologram, domain and resolution of reconstructed image.
2005, 54 (3): 1178-1183.
doi:10.7498/aps.54.1178
Abstract +
The dynamical behavior of purity and entanglement for excitions in three quantum dots placed in a cavity driven by a broadband squeezed vacuum is studied in the low exciton density regime. It is found that the excitions in the three quantum dots can evolve into a pure entangled state only when the dissipation of the cavity and excitions is negligible. When the injected field into the cavity is a squeezed vacuum, the excitions will be in a three_mode Gaussian entangled mixed state even in the long time limit .Analytical expressions are derived showing the dependence of the purity and entanglement property of the excitions in the three quantum dots on the squeezing properties of the initial state prepared in the cavity and the strength of two_photon correlations of the squeezed vacuum injected into the cavity.
2005, 54 (3): 1184-1189.
doi:10.7498/aps.54.1184
Abstract +
The evolution of the field (atomic) entropy in a system of a quasi_Λ_type fourlevel atom interacting with an uncoupled two_mode coherent field is investigated. The effects of initial atomic state, the initial mean photon number and the splitting of the atomic energy levels on the entropy are discussed. The system reduces to that of a twolevel or threelevel atom interacting with a singlemode coherent field in special cases.
2005, 54 (3): 1190-1193.
doi:10.7498/aps.54.1190
Abstract +
We present a scheme for transferring quantum information, which is based on the nonresonant interaction of two two_level atoms with a single_mode cavity field. We show that quantum information can be transferred from one atom to another atom, and from cavity mode to two atoms by manipulating the interactions between cavity field and two atoms, and the information contained in the transferred atom or cavity mode is completely erased.
2005, 54 (3): 1194-1199.
doi:10.7498/aps.54.1194
Abstract +
A frequency_resolved optical gating (PG_FROG) with polarization gating technique is developed to diagnosis the characteristics of laser pulses generated from a 20_TW femtosecond laser amplifier. Based on the data of the correlation signal in time and frequency domains, we obtained the detail information on pulse shape, bandwidth, pulse duration and phase by using the retrieval algorithm. The measured results with different phase compensation are also presented and discussed.
2005, 54 (3): 1200-1207.
doi:10.7498/aps.54.1200
Abstract +
The dispersive character of ?ffner stretcher was studied, and a concise expression of output pulse duration was presented. An ?ffner stretcher was setup experimentally, which could stretch a 19fs seed pulse to 605 ps after 4 passes in it free of aberration.
2005, 54 (3): 1208-1212.
doi:10.7498/aps.54.1208
Abstract +
Based on the theory of multi_pass amplification, we analyse numerically the character of gain for amplified pulse and design a 6_pass amplifier. With two 13J, 532nm Nd:YAG lasers as the source, amplified pulse energy as high as 1J was obtained, which corresponds to a 38% conversion efficiency.
2005, 54 (3): 1213-1217.
doi:10.7498/aps.54.1213
Abstract +
In this paper,the luminescence dynamics of X_folded cavity Ti:sapphire femto_second laser has been measured,and the self_mode_locking mechanism and process of femto_second laser have been investigated systmatically by means of propagation_circle and transform_circle graphic method.A new mode_locking mechanism,self_pulsing Kerr_lens switching and magnifying mode_locking,has been put forward.
2005, 54 (3): 1218-1221.
doi:10.7498/aps.54.1218
Abstract +
We describe the fabrication process of a two_dimensional silicon_based photonic crystal (PC) slab with partial air_bridge, which has a photonic band gap in the nearIR range .The process involves the formation of the air_bridge silicon slab by wet etching and the fabrication of periodic air holes by a focused ion beam. We successfully obtained such a sample and measured its transmission in a wide spectrum. It is found that the observed spectrum is consistent with the theoretical values calculated by the plane wave expansion method. The TM0_like modes reduce the size of the band gap, and the partial air bridge is beneficial to the fabrication of large PC slabs. Meanwhile, it is possible to draw light out from the supporting material of the air bridge.
Theoretical analysis of tunable wavelength conversion based on FWM in semiconductor fiber ring laser
2005, 54 (3): 1222-1228.
doi:10.7498/aps.54.1222
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In this paper, a comprehensive broad_band dynamic model of tunable wavelength converter based on four_wave mixing in semiconductor fiber ring laser is presented. Critical factors, e.g., the materal gain profile, the longitudinal variation of the optical field, and the broad_band spontaneous noise emission are considered in the model. By numerical simulation, the effects of the input signal power, injection current, the coupling of the output coupler and the lasing wavelength on the performance of the wavelength converter are investigated. Numerical results are in agreement with the experimental results in the literature
2005, 54 (3): 1229-1234.
doi:10.7498/aps.54.1229
Abstract +
Dispersion and polarization properties of near_rectangle core photoric crystal fibers (PCFs) were analyzed with a full vector model. The numerical results show that the modal birefringence of near_rectangle core PCF is at least one order of magnitude higher than the conventional elliptical polarization_maintaining fibers (PMFs). In order to obtain higher birefringence, an efficient way is to increase the relative hole diameter. Zero walk_off point occurs at the longer wavelength than that of convention elliptical PMF. With increasing hole pitch, the walk_off curve and zero walkoff point would shift towards the longer wavelength region. The corresponding wavelength of zero walkoff point is in proportion to the size of the hole pitch. The occurrence of zero walkoff point can efficiently restrain the first_order polarization mode dispersion. Through choosing the suitable structural parameter of near_rectangle core PCF, we can get the more flexible dispersion properties. The approximate 400nm ultra_flatten dispersion was gotten near the wavelength 155μm for a nearrectangle core PCF with Λ=2μm and d/Λ=03 This fiber has a number of potential applications in polarization control, dispersion control and management.
2005, 54 (3): 1235-1240.
doi:10.7498/aps.54.1235
Abstract +
As a precondition , it was presented that the single_mode optical fiber , the dispersion_shift optical fiber and the dispersion_flatten optical fiber can be regarded as the special examples of the index_guiding photonic crystal fiber(PCF) under a determinate condition, when the new step effective index model （SEIM） was used to discuss the chromatic dispersion properties of PCF. The result compared with the experimental data reported in the literature indicated that such a SEIM can be used to uncover more interesting dispersion regimes in PCFs. In particular, the speed of calculation by using the SEIM is very quick. Finally, the dispersion characteristics of the PCF with different air hole diameter d, air hole pitch Λ and the core radius a were also discussed.
2005, 54 (3): 1241-1246.
doi:10.7498/aps.54.1241
Abstract +
The performances of the three polarization mode dispersion (PMD) emulators commonly used today are analyzed and compared among them through numerical simulation of their differential group delay (DGD) statistical characteristics and PMD vector autocorrelation function. The results demonstrate that to produce DGD that can match theoretical distribution, one DGD generator is adequate, while at least 15 sections are necessary in the emulator built by polarization maintaining fibers and rotatable connectors. And the autocorrelation function of the emulator based on polarization maintaining fibers depends on DGD of every section, while that of the emulator based on DGD generators is smooth and can be regarded as constant outside the central frequency range.
2005, 54 (3): 1247-1252.
doi:10.7498/aps.54.1247
Abstract +
With each unit cell replaced by a system of finite freedoms of motion, two_dimensional phononic crystals can be simplified to an infinite discrete periodic system. Therefore, the elastic wave band structures of the two_dimensional phononic crystals can be calculated with a straightforward lumped_mass approach, whose computational cost is much lower than the well_known plane wave expansion(PWE) method. The numerical results of the two methods are in reasonable agreements. As the well_known Gibbs oscillations in the PWE can be eliminated with the lumped_mass method, this new approach is insensitive to the sharp variation of elastic constants on the interfaces inside the phononic crystals. Furthermore, the lumped_mass method can also be used to calculate the band structures of two_dimensional phononic crystals with arbitrary unit shapes easily.
2005, 54 (3): 1253-1260.
doi:10.7498/aps.54.1253
Abstract +
Since the sound pressures are measured on the holographic plane with a finite size, there are windowing effects and wraparound errors in the planar near_field acoustical holography (NAH) based on spatial fast Fouries transform (FFT)_based planar NAH). In order to overcome the windowing effects and wraparound errors, statistically optimal planar near_field acoustical holography (SOPNAH) is used. The sound field superposition theory is used to prove the formulas for the SOPNAH. A simple and effective method for choosing the wave number vector is proposed by means of limiting the spatial wavenumber in the kx,ky directions and discretizing the wavenumber space plane demarcated by the maximum and minimum of kx,ky. To overcome the limitation, that sound field on one side of the holographic plane must be free, in the application of the normal SOPNAH, the sound field separation technique with double holographic planes is proposed. Some results of experiment and numerical simulation are presented to demonstrate the validity of the formulas.
2005, 54 (3): 1261-1266.
doi:10.7498/aps.54.1261
Abstract +
Mechanism of broad acoustic band_gap in the two_dimensional three_component composite is investigated by calculating acoustic transmission spectra and acoustic fields for different inserted steel rows embedded in epoxy resin matrix with or without rubbers as the coating material. By comparing the acoustic fields inside the two_ and three_component crystal slabs, one can conclude that the broad acoustic band_gap in the three_component crystal slab is formed by the coexistence of the Bragg reflection of a periodic structure and the localized resonance in the soft rubber. The former is evidence in higher frequency and the latter is dominant in lower frequency with the wavelength longer than that of the coating layer.
2005, 54 (3): 1267-1272.
doi:10.7498/aps.54.1267
Abstract +
In this note, we apply the sub_sampling idea to the design of the chaotic secure communication system and analyze the Lorenz system and a kind of hyper chaotic system. The result obtained indicates that the security of the cryptosystem is not only determined by the dimension, but also related with the sampling interval. Then, we verify these two systems using the VWK (Volterra_Wiener_Korengerg) nonlinear test and surrogate data test methods.
2005, 54 (3): 1273-1278.
doi:10.7498/aps.54.1273
Abstract +
The pressure of granular mass on container bottom has been experimentally investigated in vertically vibrated granular beds. Pulse signals are found of the pressure, and the pulse strength undergoes subharmonic bifurcations controlled by the scaled vibration acceleration. Condensed state of particles is observed at the bed bottom, in which the particles are closely packed, with small free path, and move like a bulk block.
2005, 54 (3): 1279-1282.
doi:10.7498/aps.54.1279
Abstract +
The dilute granular flow distribution near the rough boundary of a two_dimensional inclined channel have been reported. It is caused by the increasing inclination and the width of the channel. Compared with the viscous fluids, the velocity profiles of the granular flow are more blunted than the parabolic form and the density profiles are nonuniform. In thie paper, we present the density of granular flux ξ near the rough boundary of a two_dimensional inclined channel. the results show that there is a critical width of channel Wc for the transition of the density of granular flux ξ=ρv, and the density of granular flux near the boundary decaying exponentially with incresaing inclination of the channel when the width of channel is less than Wc.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (3): 1283-1289.
doi:10.7498/aps.54.1283
Abstract +
We have discussed the effect of the variation of target absorptance on the temperature distribution of the target before melting. The relationship of the target absoptance with time is derived. Based on this relationship and the actual shape of incident energy density which is a Gauss distribution, the relevant heat flow equation is set up. By using the finite difference method, heat flow equation under an appropriate boundary condition is solved. We have obtained the temperature distribution as function of time and location. At the same time, we have also discussed the physical picture of a relevant process in detail. Finally, we have studied the effect of the variation of absorptance and the distribution of incident energy density on the relevant process. The result shows that during the pulsed laser process, the variation of target absorptance has an important effect on the final simulation result. If this variation is neglected, a remarkable difference can be found between theoretical results and experimental data.
2005, 54 (3): 1290-1294.
doi:10.7498/aps.54.1290
Abstract +
Long plasma channels can be formed when intense femtosecond laser pulses propagate in air. In contrast to other conventional diagnostic techniques, the acoustic method to probe the plasma channel has its advantages. By measuring the sound signals along the channel, the channel length and the distribution of electron density along it can be retrieved easily.
2005, 54 (3): 1295-1300.
doi:10.7498/aps.54.1295
Abstract +
The homogeneous barrier discharge with multiple current pulses at atmospheric pressure in helium is numerically investigated on the basis of one_dimensional fluid model. The influence of the applied voltage amplitude, frequency, as well as dielectric layer characteristics on the multiple_pulse discharge is discussed and analyzed. The simulation results show that, in the case of smaller gap width, multiple current pulses can be formed in each half_cycle of the applied voltage due to the increase of surface density of the accumulation charges, leading to the enhancement of the induced electric field. Multiple pulses correspond to separate breakdowns in the same time interval. The smaller the gap width, the bigger the number of current pulses per half cycle. The applied voltage and frequency can also influence the number and the amplitude of current pulses. However, there is no obvious influence of the barrier thickness and the permittivity on the number of current pulses.
2005, 54 (3): 1301-1305.
doi:10.7498/aps.54.1301
Abstract +
Hard and corrosion resistance (Ti, Al)N film was deposited by pulsed high energy density plasma on the substrate of 045% C carbon steel at ambient temperature. The microstructure of the film has been investigated by SEM,XRD,XPS and AES. The nanohardness of the film was tested by nanoindentation tester. The corrosion resistance of the film was tested by potentiodynamic polarization in 05 mol /L H2SO4 aqueous solution. The results indicate that the film mainly composed of (Ti, Al)N and a small amount of AlN. The nanohardness of the film approaches 26 GPa. The corrosion resistance of the film is improved by about one order of magnitude, compared with 1Cr18Ni9Ti austenitic stainless steel.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (3): 1306-1312.
doi:10.7498/aps.54.1306
Abstract +
Assuming a simple biaxial molecular interaction model in nematic liquid crystal, and using the mean field approximation, phase transitions from isotropic to uniaxial nematics, uniaxial to biaxial nematics are obtained. The result obtained shows that at certain temperatures, the biaxial phases are induced by the asymmetry of molecular shape of liquid crystal. In nuclear magnetic resonance experiment, a general relation between order parameters and spectrum frequency splitting is derived, and possible experimental measurement is discussed.
2005, 54 (3): 1313-1319.
doi:10.7498/aps.54.1313
Abstract +
In the literature, a majority of studies on thermal properties of nanocrystals have taken the thermal features of interfaces as a representative of those of the whole nanocrystal. This treatment may cause big errors in predicting some important parameters such as the transition temperatures and critical sizes of phase for transformation in nanocrystalline materials, when the grain size is larger than several tens of nanometers. In the present paper, a model to calculate the thermodynamic functions of the whole nanocrystal has been developed with the consideration of the effects of both the interfaces and the crystal in the grain interior. The expressions of the enthalpy, entropy and Gibbs free energy, as a functions of the excess free volume at interfaces, temperature and grain size, are derived for single_phase nanocrystals. Using the Co nanocrystal as an example, thermal features of interfaces and the bulk nanocrystal have been compared with the conventional. Furthermore, the characteristics of β_Co→α_Co phase transformation in nanocrystalline materials are studied, the transformation temperatures at different levels of grain size, as well as the critical grain sizes at different temperatures, are predicted and compared with experimental results.
2005, 54 (3): 1320-1324.
doi:10.7498/aps.54.1320
Abstract +
In this paper, three different atomic configurations at γ/γ′（001）interface in Ni_based single_crystalline superalloys has been studied by means of molecular dynamics. The most stable atomic configuration was obtained by energetics calculation. Among the three configurations analyzed, dynamics simulation results show that a pairs of edge misfit dislocations appeared at all the relaxed interfaces. The related calculations reveal that the system energy, the interface formation energy and the relaxed energy are determined by the stacking sequence, while the geometric character of different atomic configurations is the same. That is, different atomic configurations at γ/γ′（001）interface have the same strain relief mechanism.
2005, 54 (3): 1325-1329.
doi:10.7498/aps.54.1325
Abstract +
When we calculate the phonon dispersion relations by using the force constant parameters for two_dimensional(2D) graphite, it is necessary to consider the problem that a 3D nanotube is formed by a rolled 2D graphene sheet. The present paper reports results on phonon dispersion relations of armchair and zigzag carbon nanotubes calculated with the considerations to the effect of curvature. Based on the results of the calculations and the symmetry analysis of the structures of single wall armchair and zigzag carbon nanotubes, the decomposition of the vibration modes at the Γ point is discussed.
2005, 54 (3): 1330-1333.
doi:10.7498/aps.54.1330
Abstract +
Scanning tunneling microscopy (STM) and x_ray photoemission spectroscopy (XPS) studies of germanium growth on Ru(0001) were carried out. STM measurements showed a typical Stranski_Krastanov growth mode of Ge on Ru(0001), i.e. first atomic wetting layer is formed in the submololayer range, and the formation of islands on top of a flat first layer occurs for subsequent layers. XPS measurements showed a weak interaction between Ge and the substrate of Ru(0001). The Ru 3d5/2 and Ru 3d3/2 corelevels of Ru(0001) are located at 2798 and 2840 eV in binding energy respectively. Upon Ge growth, up to a thickniss of about 20 atomic layers, the Ru 3d corelevels shift downward in binding energy by an amount of about 02 eV，while the Ge 3d corelevel shift upward in binding energy from the Ge low coverage limit of 289 eV to 290 eV，with a relative change of 01 eV.
2005, 54 (3): 1334-1340.
doi:10.7498/aps.54.1334
Abstract +
Pb(Zr048Ti052)O3(PZT) thin films were prepared on the Pt/Ti/SiO2/Si substrates by RF_ magnetron sputtering method at room temperature. After rapid thermal annealing (RTA) and conventional furnace annealing (CFA) at different temperatures, the amorphous films were transformed into polycrystalline PZT thin films with (100) and (111) orientation, respectively. The phase formation and degree of orientation were investigated by x_ray diffraction (XRD). The surface micro_structure and ferroelectric domains formed by the spontaneous polarization in the corresponding region were observed by atom force microscopy and piezoresponse force microscopy. The distribution character of the ferroelectric domains with different preferred orientation in the films were studied. The result shows the perovskite PZT crystalline was found to hetero_nucleate epitaxially on top of the PtPb intermetallic phase at the PZT/Pt interface during RTA. The crystallizing speed along the interface is much faster than perpendicular to the film surface. While the nucleation of the films annealed by CFA dominantly homo_nucleate around the defects and impurities in the films. Different preferred orientation growth is attributed to different nucleation mechanism.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2005, 54 (3): 1341-1346.
doi:10.7498/aps.54.1341
Abstract +
Basing on ab initio methods and the elastic scattering Green function theory, we have investigated electronic transport properties of metal_molecule_metal junctions by taking the 4_4′_dimercaptodibenzene molecule as an example. The molecular geometric structures, electronic structures, and current_voltage characteristics have been studied for varying the distance between the two electrodes. Numerical results show that the changes of the distance between electrodes give various influence on the extended molecule's geometric and electronic structures, which brings effects on the electronic transport properties of the molecular systems. The equilibrium state of the extended molecule is not the best situation for electronic transportation. The characteristics of electronic transportation can thus be improved by adjusting the distance between the two electrodes.
2005, 54 (3): 1347-1351.
doi:10.7498/aps.54.1347
Abstract +
The potential and the electric field at the end of the individual nanowire under an electric field were calculated with the image charge model. With the nanowire as a field emitter, the enhancement factor was given by the expression: β０＝h/ρ+35. Taking into account the influence of the anode_cathode distance, the enhancement factor at the end of the nanowire could be adjusted based on the equation: β=h/ρ+35+A(h/d)3, where h and ρ are the length and the radius of the nanowire respectively; d is the anode_cathode distance and A is a constant. From the above results, it is concluded that the aspect ratio is the most important factor for the nanowire emitter and the anode_cathode distance also slightly influence the enhancement factor of the nanowire in field emission, and the enhancement factor increases with the decrease of the anode_cathode distance.
2005, 54 (3): 1352-1360.
doi:10.7498/aps.54.1352
Abstract +
By using the first principle method, the geometry and electronic structures of the clean VC(001) surface are investigated. Similar to the TiC(001) surface, the relaxation of the VC(001) surface leads to the C and V atoms on the top layer move outward and inward, respectively. Results of band structure calculation show that the band structures of transition metal (001) surfaces can be well described by the rigid band model. For the VC(001) surface, the surface states are mainly located around 30eV below the Fermi level, and mainly originate from the 2pz orbital of C atom in the top layer. In addition, the surface states derived from the top layer V 3d orbitals are also observed near the Fermi level. Since these states contain significant contributions of those 3d orbitals vertical to the surface (3d２z and 3dxz/dyz), which will play important roles in the surface reactions, it could be expected that the VC(001) surface exhibits different surface reactivity compared with the TiC(001) surface.
2005, 54 (3): 1361-1365.
doi:10.7498/aps.54.1361
Abstract +
By using the idea of damped harmonic oscillator operation,a mesoscopic quartz piezoelectric crystal equivalent circuit is quantized. By this basic theory, we studied the quantum fluctuation of the voltage and current in each branch of the mesoscopic quartz piezoelectric crystal equivalent circuit under the squeezed vacuum state and the vacuum state.
2005, 54 (3): 1366-1369.
doi:10.7498/aps.54.1366
Abstract +
We calculate the conductance and thermopower in saddle quantum point contact under a finite temperature and different magnetic fields. The steplike conductance becomes flatter and the length between the peaks of the thermopower becomes longer with increasing magnetic field. The quantization of the conductance is destroyed and the peak structure of the thermopower disapears when the temperature becomes higher.
2005, 54 (3): 1370-1372.
doi:10.7498/aps.54.1370
Abstract +
A pn junction is fabricated by using the pulsed laser deposition (PLD) technique for a ptype YBa2Cu3O7-δ (YBCO) film on the ntype SrNb001Ti099O3(SNTO) single crystal substrate. The measured results reveal that the YBCO thin film is highly corientated structure and shows very good superconducting properties. The YBCO/SNTO pn junction has good rectification property and stability under variation of temperature and magneticfield.
2005, 54 (3): 1373-1377.
doi:10.7498/aps.54.1373
Abstract +
This paper investigates the dependence of current and voltage characterizations on stress time in deep submicron PMOSFET's before and after negative bias temperature (NBT) stress, we mainly focus on the threshold voltage shift under NBT stress. It is experimentally demonstrated that the electrochemical reactions at the interface between gate oxide and substrate and the diffusion of hydrogen related species in the oxide are the major causes of the NBT in PMOSFET's. PMOSFET degradation caused by NBT depends on the balance of reactionlimited and diffusionlimited mechanisms.
2005, 54 (3): 1378-1384.
doi:10.7498/aps.54.1378
Abstract +
A conventional magnetron and a coaxial electrosolenoid were used to construct an unbalanced magnetron sputtering deposition system for investigating its properties. At 02Pa, argon gas discharging, a shielded planar ioncollecting electrode was taken to measure the saturation ion beam flux density at the different axial positions. The saturation ion flux reached about 9mA/cm2. The magnetohydrodynamics was applied to analyse the influences of the magnetic mirror effect on the discharge properties caused by the solenoid. As a result, the comparisons of the theoretical calculations with the experiments indicated that the model described correctly the plasma properties in the unbalanced magnetron sputtering system.
2005, 54 (3): 1385-1389.
doi:10.7498/aps.54.1385
Abstract +
Zirconium singlelayer films were prepared by ion beam sputtering method. By using a novel designed substrate holder in preplanting seeds method, the growth process of the nodular defects in thin films was studied. With the help of high resolution optical microscopy and electron scanning microcopy, the phenomenon that the nodules nucleation exhibits fractal characters in their initial growth period was observed. By using the molecular dynamics theory and diffusion limited aggregation model of film growth, the fractal phenomenon of the nodule nucleation was well explained.
2005, 54 (3): 1390-1395.
doi:10.7498/aps.54.1390
Abstract +
SrTiO3 (STO) films were deposited onto the ptype Si substrates by metalorganic decomposition (MOD) technique. The dielectric and interface characteristics of STO with a metalinsulatorsemiconductor(MIS) structure were investigated. The results showed that the dielectric constant was about 105 and the dissipation factor was lower than 001 for our STO films at a frequency of 10kHz. The excellent dielectric properties were attributed to the polycrystalline structure with good crystallinity. The fixed charge density Nf and the interfacetrap density Dit were calculated to be about 15×1012cm-2 and (14—35)×1012cm-2eV-1, respectively. Both Nf and Dit were mainly connected with an interface layer with low dielectric constant formed at the interface of Si/STO.
2005, 54 (3): 1396-1399.
doi:10.7498/aps.54.1396
Abstract +
PEN films were prepared by vacuum deposition. Their electrical bistable properties were studied under conditions of various circuit parameters.A decrease of time needed for impedance transition with increasing circuit current was observed. The film impedance showed a nonlinear characteristics and then data fitting was done for the nonlinearity. Furthermore, an energy effect was found during the transition, i.e. when the applied voltage exceeds a threshold, the energy consumption keeps invariable.
2005, 54 (3): 1400-1405.
doi:10.7498/aps.54.1400
Abstract +
The Yb275C60 thin film was prepared and studied by using the synchrotron radiation ultraviolet photoemission spectroscopy(PES) in an ultrahighvacuum system. The spectral line obtained in the range between the Fermi level and ～5 eV binding energy consists of those lines from the valence band (the molecular orbital LUMO, HOMO and HOMO1 derived energy bands of C60) and core levels(Yb 4f7/2 and 4f5/2). Taking into account the variations of the photoinization cross sections of C 2p and Yb 4f with different photon energies, we have measured the photoemission spectra under the condition of varying photon energies, and carried out simulations to deduce the component contributions. The peak positions, widths and intensities for the components are obtained quantitatively. The results reveals that the photoemission of 4f electrons has a significant intensity with the photon energies larger than ～300 eV, and that the measured spectra depart drastically from the density of states of the valence band. To observe the valence band structure, one should carry out the PES measurements by using photons with energies less than 300 eV. The photoionization crosssection oscillation is also observed in Yb275C60 with almost the same oscillation period as that for pure C60 However, the oscillation amplitude is obviously smaller than that for pure C60, which reveals that the chemical environment of C60 in compounds has nonnegligible effects on the photoionization crosssection oscillation phenomenon.
2005, 54 (3): 1406-1409.
doi:10.7498/aps.54.1406
Abstract +
We investigate the superconductivity of highTc oxides with the dp model. It is shown that the dp pairing can dominate the superconductivity. The pairing symmetry depends on the anisotropic dp interaction in CuO2 plane. The anisotropic dp interaction can lead to dwave or swave symmetry, but the repulsive interaction in the CuO2 plane cannot lead holes to being paired. The ‘preliminary pairing' may appear in a lightly doped regime. The critical temperature cannot be found for the pairing order parameter when the pairs are localized. The delocalization of holes and evolution of pairing symmetry with increasing doping are explained.
2005, 54 (3): 1410-1414.
doi:10.7498/aps.54.1410
Abstract +
A metastable state with coexistence of ferromagnetic and antiferromagnetic phases has been confirmed in compound LaFe11.4Al1.6 by thermomagnetic curves at different external fields. The temperature behavior of the critical field could be explained by taking into consideration the metastable state. The existence of the metastable state is attributed to the exchange interactions and lattice disorder.
2005, 54 (3): 1415-1419.
doi:10.7498/aps.54.1415
Abstract +
CoPt(FePt)C nanocomposite thin films were prepared by a pulsed filtered vacuum arc deposition technique. Thermal annealing was performed in vacuum at various temperatures. The dependence of the magnetic properties on the carbon fraction and annealing temperature was studied. Both xray diffraction and magnetic force microscopy analyses confirmed the formation of nanocrystallites of facecenteredtetragonal phase of CoPt or FePt in the carbon matrix after annealing at a sufficiently high temperature. For the film with particular compositions of Co24Pt31C45 and Fe43Pt35C22,the coercivity and the grain size were observed to increase with increasing annealing temperature. For the Co24Pt31C45 film at an annealing temperature of 700℃, the coercivity was 2.1×105 A/m and the grain size was about 17nm. For the Fe43Pt35C22 film at an annealing temperature of 650℃, the values were 2.8×105 A/m and 105nm,respectively.
Moving and zero-velocity gap soliton in resonantly absorbing Bragg reflector of finite atomic widths
2005, 54 (3): 1420-1425.
doi:10.7498/aps.54.1420
Abstract +
Selfinduced moving and zerovelocity(ZV) gap solitons were studied in a resonantly absorbing Bragg reflector of finite atomic width. Numerical results showed that the existence of moving gapsoliton is in general not affected by the finite atomic width but the existence of the ZV gapsoliton is highly affected by the widths of the atomic layers. Thus the trapping of the photonic energy occurs only in very thin atomic layers arranged with Bragg periodicity.
2005, 54 (3): 1426-1430.
doi:10.7498/aps.54.1426
Abstract +
The magnetoelectric (ME) effect is a product property of the composite material consisting of individual piezoelectric and magnetostrictive phases. Based on the constitutive equations of the materials, the ME coupling of a symmetrical magnetostrictive/piezoelectric laminated composite is modeled using a simple static elastic method. The ME coupling is also simulated by numerical technique employing the ANSYS 80/Multiphysics finite element software. It is found that the ME voltage coefficient in the static method is quite close to that in the equivalent circuit approach and increases with the increase of the magnetostricive/piezoelectric thickness ratio. Using the numerical modeling we can calculate the ME voltage coefficient of the magnetostrictive/piezoelectric laminated composite effectively.
2005, 54 (3): 1431-1436.
doi:10.7498/aps.54.1431
Abstract +
A method is proposed for analyzing the NMR relaxation data. The procedure includes using the nonnegative leastsquares (NNLS) to determine roughly the relaxation time values. Then those values are used as the initial parameters of the nonlinear fitting computation. As a result, accurate relaxation time data can be conveniently obtained without any preknowledge of the sample. This method is verified and demonstrated by computer simulations and NMR experimental results.
2005, 54 (3): 1437-1441.
doi:10.7498/aps.54.1437
Abstract +
Nanoscale characterization of fieldinduced displacement was made in compositionally graded PZT thin film according to the inverse piezoelectric effects by SFM in contact mode. The nanoscale piezoelectric displacement electric field butterfly loop was obtained due to the combined contribution from linear piezoelectric effect and domain switching effect, which substantiate nanoscale validity of CaspariMerz theory. The nanoscale imprint phenomena were also observed in the thin film.
2005, 54 (3): 1442-1446.
doi:10.7498/aps.54.1442
Abstract +
Oxyfluoride glass and glass ceramics codoped with Er3+/Yb3+ ions of the same composition were prepared. Nanocrystals in the glass ceramics were formed,characterized by xray diffraction and fluorescence spectra. The measurements by using the differential thermal analysis and the crystal parameter calculation by JuddOfelt theory indicated that the rareearth ions have entered the nanocrystals. At the same time, the ratio of the nanocrystalline phases in glass and glass ceramics before and after annealing was calculated respectively.
2005, 54 (3): 1447-1451.
doi:10.7498/aps.54.1447
Abstract +
Nitrogen was implanted into the chemical vapor deposition(CVD) diamond films, and the electron fieldemission properties of the nitrogenated diamond films were investigated. Raman and xray photoelectron spectroscopy(XPS) measurement revealed that nitrogenimplantation damaged the structure of diamond film and promoted the formations of sp2 C—C and sp2 C—N bonding. By increasing the implantation dose， the threshold field of the emission of the diamond film could be lowered from 18V/μm to 4V/μm. The enhancement of field emission for nitrogenimplanted CVD diamond films was attributed to the increase of the fraction of sp2 C bonds and the formation of defect bands within the bulk diamond band gap induced by nitrogenimplantation, which could alter the work function and elevate the Feimi level. Consequently, the energy barrier on diamond surface for electron tunneling was reduced.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2005, 54 (3): 1452-1456.
doi:10.7498/aps.54.1452
Abstract +
Triangular silver nanoplates with its border size of 100±10nm and thickness of 30nm were synthesized by a chemical method. These triangular silver nanoplates were characterized by TEM, UVVis spectroscopy and xrays diffraction analysis. Results obtained showed that these triangular silver nanoplates are perfect with sharp corners and selfassembled into twodimensional ordered monolayer on the carboncovered copper grid due to the adsorption of organic molecules in between these silver nanoplates. The wellaligned silver film on Si (100) substrate showed strong surfaceenhanced Raman scattering for pyridine molecules.