Vol. 54, No. 8 (2005)
2005, 54 (8): 3473-3479. doi: 10.7498/aps.54.3473
In terms of a mathematical expression of the quantitative causal principle, this paper gives a unification of Hamilton, Voss, Hlder, Maupertuis-Lagrange varia tional principles of integral style of the second-order Lagrangians, and finds t he intrinsic relations among all the different integral variational principles. It is proved that f0= 0 is just the result satisfying the quantitati ve ca usal principle． The Noether conservation charges of Hamilton, Voss, Hlder, Ma upertuis-Lagrange variational principles are shown up, and the intrinsic relatio ns among the Noether conservation charges of all the integral variational princ iples are discovered. Our investigations make the expressions of the past scrappy numerous variational principles be unified into a relative consistent system o f all the variational principles in terms of the quantitative causal principle, and show that all the variational principles become deductions of the quantitat ive causal principle.
The mean first-passage time for an asymmetric bistable system driven by multiplicative and additive noise
2005, 54 (8): 3480-3485. doi: 10.7498/aps.54.3480
In this paper, the effects of asymmetry of the potential on the mean first-passage times (MFPTs) in two opposite directions are investigated in an asymmetric b istable system driven by multiplicative noise and additive noise. We find that t he MFPTs in two opposite directions are no longer symmetric in an asymmetric bis table system. Furthermore, we calculate the MFPTs of an asymmetric Duffing model . Numerical results show that: (1) The MFPTs depend on the initial states in th e asymmetric bistable system, namely, T+(xs1→xs2) is not equal to T-(xs2→xs1). (2) The effec ts of noise intensity on the MFPTs T+(xs1→xs2) and T-( xs2→xs1) are different in the same kind of parameter plan e. There exists a peak on each of the curves of lnＴ- versus Ｄ,as we ll as the “resonant activation”, while the variation of lnＴ+ ver sus Ｄ is monotonic. (3) The influence of the asymmetry coefficient r on Ｔ± is entirely different. The curves of lnT- versus r have mon o-valleys but the variation of lnＴ+ versus r is monotonically risi ng.
2005, 54 (8): 3486-3490. doi: 10.7498/aps.54.3486
The characteristics of the Genesio-Tesi and Coullet systems are analyzed. Two systems are topologically inequivalent, but they have similarity in the strange attractor structure. Chaos synchronization between the two systems is realized via nonlinear feedback control. The nonlinear feedback controller is designed based on the stability theory， and the area of feedback gain is taken. The simulatio n result verifies the conclusion.
2005, 54 (8): 3491-3496. doi: 10.7498/aps.54.3491
Phase synchronization dynamics of Rssler oscillator in two coupled harmonic oscillators is discussed based on stability analysis of the coupled chaotic system. Different from the case of only one coupled periodic oscillator, in two o scillators one or the other harmonic oscillator will entrain alternately (or th ey will entrain exclusively). We find that depending on the stability of the system, the duration of the phase synchronization is affected by parameters of t he oscillator. The simulated results agree with our theoretic values within the range of error.
2005, 54 (8): 3497-3501. doi: 10.7498/aps.54.3497
The conditional entropy is used to assess the generalized synchronization of bidirectionally coupled chaotic systems. By increasing the coupled strength, the generalized synchronization appears when there is a sharp minimum of the conditional entropy. We apply this criteria to the case of the coupled Rssler-Lorenz an d Rssler-Rssler system to test our method. Numerical results show that it is very effective and robust.
2005, 54 (8): 3502-3507. doi: 10.7498/aps.54.3502
The method of chaotic control system based on adaptive pulse perturbation is pro posed this paper. Combining the method of parameter pulse perturbation with the adaptive control policy, the adaptive controller that can produce appropriate pu lse strength to realize chaos control is designed. The system can be stabilized to the different periodic orbits or fixed points by using the method to simulate the chaotic Rssler continuous system and Hnon discrete map. Furthermore, the simulation results showes that this control method has strong robustness.
Period-doubling bifurcation analysis of stochastic van der Pol system via Chebyshev polynomial approximation
2005, 54 (8): 3508-3515. doi: 10.7498/aps.54.3508
Chebyshev polynomial approximation is applied to the period-doubling bifurcation problem of a stochastic van der Pol system with bounded random parameters and subjected to harmonic excitations. Firstly, the stochastic system is reduced to its equivalent deterministic one, through which the response of the stochastic s ystem can be obtained by numerical methods. Nonlinear dynamical behavior related to various forms of stochastic period-doubling bifurcation in the stochastic sy stem is explored. Numerical simulations show that similar to their counterpart i n deterministic nonlinear system, various forms of period-doubling bifurcation m ay occur in the stochastic van der Pol system, but with some modified features. Numerical results also show that Chebyshev polynomial approximation can provide an effective approach to dynamical problems in stochastic nonlinear systems.
2005, 54 (8): 3516-3522. doi: 10.7498/aps.54.3516
Based on the Nagel-Schrekenberg(NS) model,we present a mixing traffic flow model for a two-lane traffic system. In this model,the stochastic noise P in NS model is replaced by accelerating probability Pa and braking probabil ity Pd. The fundamental diagrams of the mixing traffic under differen t conditi ons are given by the numerical simulations. We found that the lane-changing prob ability,the mixing rate and acceleration, the braking probability have a great i nfluence on the mixing traffic flow. The slow cars have a decisive action on the mixing traffic.
2005, 54 (8): 3523-3529. doi: 10.7498/aps.54.3523
A multi-step Monte-Carlo method is established for calculating the γ spectrum of plutonium volume source. The γ spectra of a spherical plutonium source is calculated by using a multi-step and direct mothed,and compared with the expe rimental γ spectrum. The calculated results are in agreement with the experm ental results whithin 10%. It is proven by the calculated result of Steve Fett er model that the multi-step calculation converges faster than the direct metho d in the calculation of the γ spectrum of plutonium volume source with shields .
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (8): 3530-3534. doi: 10.7498/aps.54.3530
Using B-spline method, we take Be3+ in buckyminister fullerence as a n example and have calculated the 2s—3p oscillator strength of the endohedrally confined hydrogen-like system in the confining well with different shapes and l ocations. Resonance enhancement appears as the 2s and 3p states are both bound i n outer well, and a resonance enhancement peak has been found at the “collapse point”. Our results show that resonance enhancement is insensitive to the shape of the confining well, and it is also influenced by confinement ability. The lo cation of the confining well may strongly affect the resonance enhancement.
Improvement of the measuring precision by changing the pulse sequence in the three-level atom gravimeter
2005, 54 (8): 3535-3541. doi: 10.7498/aps.54.3535
We introduced a method that can improve the measurement precision of the three-level atom gravimeter by changing the sequence of the pulses. A 3×3 matrix is put forward to describe the propagation of atomic beams, the interaction between the three-level atoms and bichromatic laser fields, and to calculate the phase difference of the atom interferometers. We obtained also the relation between g ravity and the phase difference of the atom gravimeter. It is found that the pre cision of the three-level atom gravimeter can be increased simply by change the sequence of the optical pulses.
2005, 54 (8): 3542-3547. doi: 10.7498/aps.54.3542
Based on the nonperturbative quantum electrodynamics, we study the high-order above-threshold ionization (ATI) induced by rescattering process. By using a form al scattering theoretical approach, an analytic form of the high-order ATI spect rum is obtained. We discuss the interference effect of different ATI channels on the high-order ATI. The high-order ATI spectra due to the rescattering of electrons from different incident angles are also given.
Absolute differential, elastic integral and moment transfer cross sections for electron scattering from O2 and CF4 at intermediate- and high-energies
2005, 54 (8): 3548-3553. doi: 10.7498/aps.54.3548
A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the absolute differential cross sections, the elastic integral cross sections, and the moment transfer cross sections for electron scattering from O2 and CF4 i n the energy range 300—1000eV by using additivity rule model at Roothaan-Hartree-Fock level. The quantitative absolute differential cross section, elastic integral cross secti on, and moment transfer cross section results are compared with those obtained b y experiments and other calculations wherever available, and good agreement is o btained. It is shown that the additivity rule model together with the complex op tical model potential modified by incorporating the concept of bonded atom can g ive better results than the one unmodified by it. So, the introduction of the bo nded-atom concept in complex optical model potential betters the accuracy of the absolute differential cross sections, the elastic integral cross sections, and the moment transfer cross sections.
Distribution of electron clouds in the excited atomic state in electron-photon coincidence scattering experiment
2005, 54 (8): 3554-3558. doi: 10.7498/aps.54.3554
Based on the general theory of the electron-photon coincidence experiment, the S tokes parameters of an excited atomic state were calculated with the distorted w ave Born approximation. According to the correlation between experiment and theo ry, the distribution of electron clouds in an excited atomic state can be descri bed by their orientation and alignment parameters. The values obtained are in g reement with the results of the experiments.
2005, 54 (8): 3559-3564. doi: 10.7498/aps.54.3559
We have measured the spectra and yields for Ar K and Mo L x-rays from Ar 15+ and Ar16+ ions colliding with molybdenum (Mo) surfaces . The spec tra and yields are measured as a function of the projectile kinetic energy. In t he case of Ar15+ -Mo, both Ar K x-rays and Mo L x-rays are observe d, and the yields of Ar K x-rays are related to the projectile kinetic energ y, the potential energy of hollow atom formed in the interaction, the competitio n of the x-rays emitting from the projectile and the target etc. But in the case of Ar15+-Mo, Mo L x-rays are observed only. The yields of Mo L x- rays induced in both cases increase with the projectile kinetic energy.
2005, 54 (8): 3565-3570. doi: 10.7498/aps.54.3565
The equilibrium geometries and electronic structure properties of mixed Aun Xm(n+m=4, X=Cu, Al, Y) have been obtained by using the B3LYP hybrid wh ich is based on non-local density functional theory method. The binding energies, ionization potential, electron affinity, the highest occupied molecular orbital ener gy level, lowest unoccupied molecular orbital energy level,and the energy gaps o f them have been calculated. By analyzing the properties of electrons using the Mulliken population method, it is concluded that impurity increases the stabilit ies of Au cluster. When Cu, Al and Y doped in Au4 cluster, the energy gaps reduce and the binding energies increase.
2005, 54 (8): 3571-3577. doi: 10.7498/aps.54.3571
The possible geometrical and electronic structures of small Pd-Y clusters including Pdn（n=2,3,4）,Yn（n=2,3,4）, PdYn（n=2,3, 4）, PdnY(n=1,2,3,4) and Pd2Yn（n=2,3,4） have been optimized by density functional theory method with a relativistic effective core potentia l(RECP) using Gaussian 98 code. Due to the Jahn-Teller effect, the ground states of Pd4 and Y4 belong to Cs, while the symmetry is C2v for P d3 and Y3. The ground states of Pd3Y, Pd4Y, PdY3,PdY4 and Pd2Y4b elong to Cs. Finally, the energy level distribution, highest occupied mole cular orbit-lowest unoccupied molecular orbit gaps and the chemical activation a re investigated.
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (8): 3578-3583. doi: 10.7498/aps.54.3578
Bitron, as a new type of high-power microwave device, is studied in this paper. The parameters (such as microwave power and its efficiency) based on the theoretical analysis has been realized on 25D Particle in Cell (PIC) simulation code. This device is composed of two parts: a modulation cavity and an output cavity . Coupling exists between these two cavities, so the oscillation occurs under ce rtain conditions. X band bitron is designed in this paper, and its theoretical e fficiency is 294%. The process is also realized by 25 PIC simulation code, w ith an efficiency 28%, microwave frequency 942GHz, and the power output 2 25GW.
2005, 54 (8): 3584-3590. doi: 10.7498/aps.54.3584
Wiggler radiation contains not only the usual component with short wavelength radiation but also a broadband component in the long wavelength region, which emits in the near forward direction, peaked at an angle 1/γ. Firstly, spontaneous radiation from a wiggler is analyzed based on the basic formula of electrody namics. With the long wavelength approximation, a formula for the long wavelengt h is obtained. The theoretical result is well coincided with the result of numer ical calculation. Also the character of this radiation is analyzed. Secondly, th e photon fluxes coming separately from the wiggler and a bending magnet are comp ared, for the wavelength longer than 1μm. The result shows the superiority of w iggler radiation in the infrared region. Finally, the long wavelength radiation from the wiggler is compared with the undulator transition radiation and the ben ding magnetic edge emission. The result shows that long wavelength radiation fro m the wiggler is the strongest one.
2005, 54 (8): 3591-3596. doi: 10.7498/aps.54.3591
A new approach to calculate the temporal aberration coefficients of dynamic electron optical imaging systems is put forward in this paper. A new definition o f temporal aberration is given in which a certain initial energy of electron emi ssion along the axial direction εz1(0≤εz1≤ε0max) as a cr iterion is considered. The new method for calculating the temporal aberration c oefficients of dynamic electron optical imaging systems named “direct integral method" is presented which gives new expressions of the temporary aberration coe fficients expressed in integral form. The difference between “direct integral m ethod" and “τ-variation method" is that the “τ-variation method" n eeds to solve the differential equations for the three of temporal geometrical a berration coefficients of second order, while the “direct integral method" need s only to carry out the integral calculation of them, which is more convenient a nd suitable for computation in the practical design.
Test and verification of temporal aberration theory for electron optical imaging systems by an electrostatic concentric spherical system model
2005, 54 (8): 3597-3603. doi: 10.7498/aps.54.3597
On theory of temporal aberration of dynamic electron optical imaging systems, we have put forward two methods: “τ-variation method" and “direct integral method" to calculate the temporal aberration coefficients. The difference betwe en them is that the “τ-variation method"needs to solve the differential eq uations for geometrical temporal aberration coefficients of second order, while the “direct integral method" needs only to carry out the integral calculations. The aim of the present paper is to test and verify the correctness of the two m ethods using an electrostatic concentric spherical system model. Results show th at these two methods can obtain identical solutions and the solutions of tempora l aberration coefficients of dynamic electron optical imaging systems are the sa me with the analytical solutions. Thus it can be concluded that these two method s are equivalent and correct, but the “direct integral method" is more convenie nt for computation and it could be suggested to use in the practical design.
2005, 54 (8): 3604-3609. doi: 10.7498/aps.54.3604
With the disk reflectivity optional and with the recording information distribut ion discretionary, this paper analyzes the readout and crosstalk in photochromic dual-wavelength storage, establishes the models for them, and presents a method to reduce the readout crosstalk. It shows that as the crosstalk of the readout of a laser corresponding to a certain material is canceled, the parameter of the method is determined only by the molar extinction coefficient of the other mate rial, and the parameter is irrelative to the disk reflectivity distribution and the recording information, even irrelative to the molar extinction coefficient of the former material. This point is validated in the readout crosstalk cancelin g experiments with the two kinds of diarylethene with different absorption spect ra.
Split Monte Carlo for impulse responses on the infrared indoor channels on the basis of Phong’s model
2005, 54 (8): 3610-3615. doi: 10.7498/aps.54.3610
A split Monte Carlo (SMC) algorithm, based on the Phong's model, for the estimation of the impulse response on the infrared indoor channels is presented. It can be applied to the indoor channel including various reflection patterns, includi ng diffuse, mirror and other non_Lambert reflections.The simulation of the indoo r optical channel by SMC method based on the Phong's model can benefit significa ntly the design of high performance infrared systems. The calculation is much fa ster than the classical deterministic method, and the speed advantage is more ob vious at a large number of reflections.
2005, 54 (8): 3616-3621. doi: 10.7498/aps.54.3616
We present in this paper a detailed discussion of the velocity_selective coherent population trapping of an atomic system in a nondegenerate Λ three_level configuration.Compared with the case of degenerate ground states and laser_atom resonance,the most probable value of the atomic_momentum distribution greatly decreases and much longer trapping time is needed in order to generate the same trapping effect.
2005, 54 (8): 3622-3626. doi: 10.7498/aps.54.3622
A stable long-distance quantum key distribution system which has been just completed in our laboratory is demonstrated in this paper. The idea of “plug and pl ay" was adopted to automatically compensate the polarization mode dispersion and phase shift. A symmetrical capacitance-balance technique and magic-T network were used in the single-photon detection module, wherein a detection efficiency of more than 5% and a dark count probability of lower than 29×10-6/p ulse were achieved. As a result, we have realized stable (longer than 12 h) quantum k ey distribution experiment in 506 km single mode fiber with mean photon number of 007 and quantum bit error rate of 4%.
2005, 54 (8): 3627-3631. doi: 10.7498/aps.54.3627
The properties of the output optical image are investigated by taking squeezed c oherent states as the input image in the parametric image amplifier.Our results show that the squeezing degree and squeezing direction of the output optical ima ge can be controlled by the parametric image amplifier,namely,the increase or de crease of the squeezing degree and the change of the squeezing direction are dep endent on the parameter selection of the parametric image amplifier.
2005, 54 (8): 3632-3636. doi: 10.7498/aps.54.3632
We report a theoretical study of linear and nonlinear susceptibilities of Raman transition in a Λ-type three-level atomic system. In the Raman transition, if t he population of atoms is all prepared in the ground state which interacts with the control light, the linear susceptibility equals zero, while the third-order nonlinear susceptibility does not equal zero. By decreasing the nonradiative dec ay rate γ12 between the two ground states of the atoms, the Kerr no nlinear refractive index for cross-phase modulation can be significantly enhance d.
Bright amplitude-squeezed light generation by an optical parametric deamplifier in a periodically poled KTiOPO4 crystal
2005, 54 (8): 3637-3640. doi: 10.7498/aps.54.3637
We demonstrated experimentally the generation of bright amplitude-squeezed light by a continuous-wave quasi-phase-matched degenerate optical parametric deampl ifier based on periodically poled KTiOPO4The threshold of the optic al parame tric oscillator is 35mW. With the pump power of 20mW, the amplitude noise re duction of 223dB is observed directly. It is significant that the amplitude noise reduction of 217dB can be observed only at the pump power of 8mW.
2005, 54 (8): 3641-3645. doi: 10.7498/aps.54.3641
In this paper we have calculated the absorption and dispersion of the probe laser in the four_level Y_type atom system at low light levels and found that if the external light fields are changed,the system would exhibit an electromagnetically induced transparency effect.At the same time,we found that the system could also exhibit enhancement accompanied with a big negative refractive index,and if the light field phase is changed,the absorption and dispersion of the probe laser are also changed.
2005, 54 (8): 3646-3650. doi: 10.7498/aps.54.3646
The method of laser_induced crystallization combining with the phase-shifting grating mask (PSGM) was carried out to fabricate nanocrystal silicon (nc-Si) with the two-dimensional (2D) patterned distribution within a-SiNx/a- Si:H/ a-SiNx sandwiched structure grown on the SiO2/Si or fuse d quartz subst rate by plasma-enhanced chemical vapor deposition technique. The thicknesses of a-Si:H and a-SiNx layer are 10 and 50nm, respectively. The results of at omic force microscopy, cross-section transmission electron microscopy and high r esolution transmission electron microscopy show that the controllable crystalliz ed regions within the initial a-Si:H layer are selectively formed with a diamete r of about 250 nm and are patterned with the same 2D periodicity of 20 μm as that of the PSGM. Si nano-crystallites，the size of which is almost the same as the thickness of the a-Si:H layer, are formed in the crystallized regions, and h ave preferred orientation.
2005, 54 (8): 3651-3656. doi: 10.7498/aps.54.3651
A theoretical study on 13μm GaAs-based quantum dot vertical-cavity surface- emitting lasers (VCSELs) was made. Investigation of the influence of VCSELs on t he optical confinement factors and the optical loss and the calculation of the m aterial gain of the assembled InGaAs/GaAs quantum dots. Analysis of the threshol d characteristic was made and the multi-wavelength cavity and multilayer quantum_dot stack structure is found to be more suitable for quantum dot VCSELs.
Calibration of interferometric autocorrelation trace for femtosecond pulse in frequency domain and the real-time chirp diagnostic for Ti:sapphire oscillator
2005, 54 (8): 3657-3660. doi: 10.7498/aps.54.3657
The time delay of interferometric autocorrelation trace of femtosecond pulse was calibrated in frequency domain. By virtue of the calibrated interferometric aut ocorrelation trace, root-mean-square width and chirp parameter of the femtosecon d pulse to be measured were calculated. Based on these parameters, the Ti:sapphi re oscillator was optimized to generate 115fs pulse in full width at half ma ximum, which was very close to the width of the transform-limited pulse. The mea surement involved only an integration and a fast Fourier transform. Consequently , real-time chirp diagnostics for Ti:sapphire oscillator was feasible.
2005, 54 (8): 3661-3664. doi: 10.7498/aps.54.3661
The optical limiting effect of solubilized carbon nanotubes on 1064 and 532nm laser is studied in experiment. The experiments are carried out with samples of different thickness and concentration, and the optical limiting experiments are also carried out with pure solvent (chloroform) in order to confirm that the opt ical limiting effect is due to carbon nanotubes. The results showed that the sol ubilized carbon nanotubes have good optical limiting characters to both 1064 and 532nm laser.
2005, 54 (8): 3665-3669. doi: 10.7498/aps.54.3665
Pulse self-compression in air is experimentally demonstrated by use of 1kHz femtosecond laser pulses with input power on the order of GW. Under the conditions of different initial chirps, the temporal and spectral characteristics of the output pulse after being focused in air are studied in detail as a function of i nput pulse energy. The experimental results show that, the temporal duration of high-intensity femtosecond laser pulses could be shortened solely through nonlinear propagation in air, without any additional dispersion compensation. Moreover, with the input pulse negatively chirped, we observed that the spectrum and pulse duration could be compressed simultaneously, and near sech2 trans form-limited output pulses shorter than original laser pulse source were obtained.
2005, 54 (8): 3670-3674. doi: 10.7498/aps.54.3670
The high-order collinear and non-collinear quasi-phase matching harmonic generations were realized in a two-dimensional periodically poled LiNbO3 wit h square lattice by tuning the input wavelength. The output spots lay at different symme tric positions with respect to the input beam of picosecond pulse, and the relat ive intensities of spots at certain wavelengths were measured. The high-order no nlinear harmonic processes were also realized by tuning the input angle. The exp erimental and theoretical results are in good agreement with each other. Our stu dies might be beneficial to the development of optics integration and compact de vices.
2005, 54 (8): 3675-3679. doi: 10.7498/aps.54.3675
For femtosecond optical parametric amplification (OPA) pumped with a 400nm blue laser, limited by phase-matched condition and nonlinear crystal transparent range, the tuning range of the output parametric laser is restricted, and the blue and the near UV lasers with wavelength less than 460nm are difficult to obtain. In our experiment, we adopted the second harmonic of a Ti:sapphire nine-pass chirp pulse amplifier at 1kHz repetition rate as the pump beam, and the white- light supercontinuum as the seed beam; thus, by a type-Ⅰ noncollinear phase-mat ched broad bandwidth β-BaB2O4 (BBO) OPA, with certain exp erimental paramete rs, the amplified signal beam from 530nm to 810nm and the idler beam from 81 0nm to 17μm were obtained; at the same time, the idler second harmonic fr om 410nm to 700nm was obtained also. The idler second harmonic was cascaded with the idler beam, its pulse energy was 26μJ and the conversion efficienc y was greater than 5%. Therefore, femtosecond pulses tuned continuously from 410 nm to 810nm can be obtained by the BBO OPA with a single crystal only, there by a useful source is provided for more investigations and applications. In this paper, we also have theoretically analyzed the generation condition of the idle r second harmonic for femtosecond OPA.
Controlling the bistability and self-pulsation characteristics of two-segment bistable laser diode based on delayed optoelectronic feedback
2005, 54 (8): 3680-3687. doi: 10.7498/aps.54.3680
In this paper, the delayed optoelectronic feedback is introduced to the absorption region in order to control the bistability and self-pulsation characteristics of the two-segment bistable laser diode (TBLD). The rate equations have been used to model numerically the effects of feedback gain and delay time. The result s show that the stable region of TBLD varies periodically with the delayed time; the bistable region shrinks with increasing delay time; the stability can beenhanced at certain values of delayed time, and the instability can be reached more easily for negative optoelectronic delayed feedback.
2005, 54 (8): 3688-3693. doi: 10.7498/aps.54.3688
The propagation of optical beams in nonlocal nonlinear media is modeled by the nonlocal nonlinear Schrdinger equation.In this paper,discussed is the propagation properties of the optical spatial solitons in the media to different degrees of the nonlocality.An iteration algorithm based on the split_step Fourier method is presented to obtain the solutions of the solitons. The profiles of the solitons to different degrees of the nonlocality are numerically obtained in the assu mption that nonlinear response of the media is Gaussian. The stability of the so lutions is also demonstrated numerically,which shows that the stable solitons ca n survive to different degrees of nonlocality. The amplitude profiles of the sol iton transit gradually and continuously from a Gaussian function in the strongly nonlocal case into a hyperbolic secant function in the local case. The critical power for the solitons decreases as the nonlocality decreases. The weaker the n onlocality,the slower the soliton phase that has a linear relation with the prop agation distance increases.
2005, 54 (8): 3694-3697. doi: 10.7498/aps.54.3694
The thermal stability, Raman spectra, and upconversion luminescence spectra of lead halide-modified Tm3+/Yb3+-codoped tellurite glasses ha ve been investigated, and the upconversion luminescence mechanism of Tm3+/Yb 3+-codoped oxyhalide tellurite glasses were analyzed. The results sho wed that mi xed lead halide-modified Tm3+/Yb3+-codoped tellurite glass es possess good thermal stability, low phonon energy and intense upconversion blue lumines cence, which indicates that mixed lead halide-modified Tm3+/Yb3+ -cod oped tellurite glasses can be used as a kind of potential host materials for upc onversion blue lasers.
2005, 54 (8): 3698-3702. doi: 10.7498/aps.54.3698
Two novel fluorene_based derivatives 9_(7_(9H_carbazol_9_yl)_9, 9_bis (2_ethylhexyl)_9H_fluorene_2_yl)_9H_carbazole (abbreviated as DCZF) and 2, 7_bis (4_metho xystyryl)_9, 9_bis (2_ethylhexyl)_9H_fluorene (abbreviated as BMOSF) were synthe sized and their linear absorption and one_photon fluorescence spectra were measu red. We used a 38ps, 1064nm Nd:YAG pulsed laser operating at 10 Hz to invest igate the three_photon absorption (3PA) properties of the two compounds. The re sults show that the linear absorption band of the two compounds is from 270—420 nm with absorption peaks at 330 and 380nm. The fluorescence bands were locat ed in the blue_violet region with the peak wavelengths of 369 and 442 nm, and s mall Stokes shifts were observed. Nonlinear absorption coefficients γ deriv ed from 3PA fitting curves are 678 and 592×10-20 cm3/ W2, respectively. Large optical power limiting induced by 3PA has also been demonstr ated for both dyes. When the incident irradiances reach 8 and 6 GW/cm2, t he limiting nonlinear transmissions of DCZF and BMOSF can reach to 30% and 45%, respectively.
2005, 54 (8): 3703-3706. doi: 10.7498/aps.54.3703
We have studied the photonic band of dual_periodic one_dimensional(1D) photonic crystals. The band splits into many sub_bands when we modulate periodically the thickness of the unit of the 1D photonic crystal. Some narrow bands appear in th e gap of the simple photonic crystal with single_period. The field of the electr omagnetic modes in the split bands exhibits dual_periodicity. The modes in the n arrow bands are localized, but those in the wider bands are extended.
2005, 54 (8): 3707-3710. doi: 10.7498/aps.54.3707
Thin_film one_dimensional photonic crystal omnidirectional reflector used in vis ible region can be achieved by using angle domain overlapping reflectance bands. By using this method, the relative band width of the omnidirectional reflector consisting of four TiO2/SiO2 thin_film photonic crystals i s up to 41 33%. By comparison, the relative band width of the omnidirectional reflector c onstructed under the same condition as the above is only 1426% by using the co nventional frequency domain overlapping. The basic principle of the angle domai n overlapping is described. A thin_film one_dimensional photonic crystal omnidir ectional reflector used in visible region is calculated and given. Meanwhile, th e omnidirectional reflector used in ultraviolet region can be constructed by usi ng this new method, which cannot be obtained by the conventional method.
2005, 54 (8): 3711-3715. doi: 10.7498/aps.54.3711
The uniplanar compact photonic_bandgap (UC_PBG) is a periodic planar layered str ucture which is constructed in the microstrip structures. In this paper, the sub strate is regarded as an uniaxial anisotropic medium, and the UC_PBG is analyzed using the method of lines (MoL). The process of MoL is described in detail, som e UC_PBGs with different dielectric parameters are computed. It is shown that th e complete band gaps or even larger ones appear in dispersion diagram of those UC_PBGs.
Wavelet transform analysis for phase reconstruction of spectral shearing interferometry of ultrashort optical pulses
2005, 54 (8): 3716-3721. doi: 10.7498/aps.54.3716
We introduce the wavelet transform for phase reconstruction of SPIDER in this pa per. With the technique, we can directly read the phase from the wavelet transfo rm of spectral interferogram, which essentially eliminates the phase noise resul ting from improper temporal filters in the conventional Fourier method. The simu lation and the practical example proved the validity and reliability of this tec hnique. This technique will find more applications in generation and characteriz ation of monocycle optical pulses.
2005, 54 (8): 3722-3725. doi: 10.7498/aps.54.3722
Based on a measured peak transmittance of a narrow band filter, the extinction coefficients of weakly absorbing thin films in a multilayer system can directly be calculated. This is a new method used for determination of the extinction coefficients of thin films in a weakly absorbing multilayer system with very easy to do and very high precision. The absorbing expression in a weakly absorbing interference narrow band filter is deduced. The principle of determination of the extinction coefficient is illustrated and the precision of the calculated extinction coefficient in a Ta2O5/SiO2 filter used in a dense wavelength division multiplexing system is analyzed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Relationship between lattice parameters and compositions of molecular beam epitaxial Hg1－xCdxTe films
2005, 54 (8): 3726-3733. doi: 10.7498/aps.54.3726
High_resolution x_ray diffraction technology is applied to the measurement of la ttice parameters and the study of strain for Hg1-xCdxTe fi lms gr own by molecular beam epitaxy. The results show that there exist both perpendicu lar strain and shear strain in Hg1-xCdxTe films. Based on crystal elastic theory, strain states in Hg1-xCdxTe films are analyz ed and calculated, and the lattice parameters of 1-xCdxTe film s at the relaxation state are obtained. It is found that the relationship betwee n lattice parameters and compositions of Hg1-xCdxTe films agrees with Vegard's law, rather than Higgins formula proposed in earlier research. It is also found that the lattice parameters can be derived from the measured data of (224) plane spacing, and that the compositions of Hg1-xCdxTe films can also be evaluated by using Vegard's law with an error about 0 01.
Nanotube rings were fabricated with a high yield by heating the lightly etched c arbon nanotubes under ambient conditions that were produced by chemical vapor deposition method. These rings, typically 300nm in diameter, were characterized using atomic force microscopy, transmission electron microscopy and scanning ele ctron microscopy. The structure and yield of nanotube rings depended strongly o n the heating temperature and time. Our researches suggest that the optimal heat ing temperature ranges from 510 ℃ to 530 ℃, and that the heating time up to 1 20 min is favorable for the increase of the yield. At high temperatures, the est erification of carboxyl functional groups attached at the nanotube ends resulted in the bending of straight nanotubes into closed rings.
A phase-field simulation on the influence of thermal fluctuation on secondary branch growth in undercooled melt
2005, 54 (8): 3740-3744. doi: 10.7498/aps.54.3740
The dendritic growth in an undercooled melt of pure substance is simulated by a phase_field model. The relationship between the dendritic growth and the parameters used in phase_field method (including undercooling, anisotropic coefficient, magnitude of thermal fluctuation) has been studied quantitatively. By employing the thermal fluctuations the birth of secondary branches has been successfully simulated. The spacing and amplitude of the secondary branches are obtained, which are in reasonable agreement with those by using the Wentzel_Kramers_Brillouin approach. Simulations indicate that the undercooling and the anisotropic coefficient have remarkable influence on the growth of the secondary branches, in which secondary branch spacing decreases with the increase of undercooling, but increases with the increase of anisotropic coefficient. The amplitude of the secondary branch decreases with the increase of anisotropic coefficient. Thermal fluctuations show strong influence on the amplitude of the secondary branch, however show less influence on the secondary branch spacing.
2005, 54 (8): 3745-3748. doi: 10.7498/aps.54.3745
Cerium_doped lutetium pyrosilicate（Ce:LPS）crystal was grown by Czochralski met hod. X_ray diffraction analysis showed that the structure of Ce:LPS crystal was monoclinic with space group of C2/m. Cleavage (110) of the crystal was obse rved by optical microscope. Optical absorption, excitation and emission spectra of Ce:LPS crystal were measured at room temperature. Results indicated that both absorption and excitation spectra of Ce:LPS showed two broad bands peaking at 3 02 and 349 nm, assigned to the Ce3+ 4f1→5d1 tr ansitions. The Gaussian fits to the emission spectra excited at 349 nm, showed band characteri stics with two peaks at 384 and 407 nm, in which the latter intensity was highe r than the former.
2005, 54 (8): 3749-3756. doi: 10.7498/aps.54.3749
Colored conical emission via spatiotemporal modulational instability was observe d in second harmonic generation of untrashort laser pulses. By injecting accurat ely synchronized white_light super_continuum seed pulses, frequencies with maxim al gain corresponding to the seed angle were amplified. The amplified pulse exhi bited 150 μJ pulse energy and 60 nm spectral width (full width at half maximum) centered around 500 nm. Wide tunable range of the output wavelength up to 290 n m was realized by adjusting the input angle of the seed pulses.
2005, 54 (8): 3757-3763. doi: 10.7498/aps.54.3757
Based on the equilibrium of combined girders, a set of models for the strain a nd stress distributions in heterostructures introduced by lattice mismatch, ther mal mismatch and the combination of the two factors are set up, and the analyti c solutions, including lattice mismatch strain, thermal mismatch strain, bending strain and the radius of curvature of the system, are also given. Furthermore, by using the models given here, strain and stress distributions in HgCdTe/CdZnTe heterostructures are calculated. The results show that both the maximum stress in HgCdTe films and the maximum stress in CdZnTe always appear at the interface between them, and that the neutral axis as a function of thickness and elastic parameters in the heterostructures are not related to lattice mismatch, lattice relaxation, thermal mismatch, and so on. In addition, the radius of curvature of HgCdTe/CdZnTe decreases with decreasing thickness of CdZnTe. In order to avoid cracking of HgCdTe/CdZnTe device at 77K, the thickness of CdZnTe must b e larger than the limited value.
2005, 54 (8): 3764-3767. doi: 10.7498/aps.54.3764
The t_J model is one of the most important models that is often used to stud y the theory of the effect of strong electron correlations and high_Tc superconductivity. In this article, the method of renormalization group is use d to investigate the t_J model， and the elementary excitation energy spectra of t_J model (Ｔ≠０) are obtained by the flow equations. The result is compared with that of Green's function method and agrees with its result. At th e same time, the result of renormalization group method is the analytical soluti on while that of Green’s function method is the numerical solution.
2005, 54 (8): 3768-3773. doi: 10.7498/aps.54.3768
With a diamond fractal lattice, the Ising model was exactly solved by parameter_ transformation technique. The rigorous partition function, free energy and corre lation functions were obtained for zero as well as non_zero field. In particular , an equation of cumulant pair correlation function and its analytical asymptoti c expression was derived in the zero field. The result indicated that the corre lation behaviors of the Ising model on a diamond fractal lattices are similar to the two_dimensional transitionally invariant lattices.
2005, 54 (8): 3774-3779. doi: 10.7498/aps.54.3774
To reveal the interfacial phase structure and its effect on mechanical propertie s of Ti_Si_N composite films, x_ray diffractometry, high_resolution transmission electron microscopy, Auger electron spectroscopy, and microhardness tester were employed to investigate theinterfacial phase structure and mechanical pro perties of magnetron sputtered Ti_Si_N composite films. A series of TiN/Si3 N4 multilayered films in nanometer scale were also prepared and characte rized for comparison. The results indicated that Ti_Si_N composite films formed a structure of nanocrystalline TiN surrounded by Si3N4 int erfacial p hase. In the Ti_Si_N composite film with lower silicon content, the Si3 N4 interfacial phase with a thickness of less than 1 nm crystal lized and formed a coherent interface with TiN nanocrystals, leading to an enhancement in the hardness of the film. Whereas, in the composite film of larger silicon cont ent, Si3N4 phase existed as amorphous and resulted in a de crease in hardness. Our research indicated that the crystallization of Si3N4 i nterfacial phase was essential to obtain a high hardness in the Ti_Si_N composit e films, and the strengthening mechanism of the composite films appeared to be the same as TiN/Si3N4 multilayered films.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2005, 54 (8): 3780-3786. doi: 10.7498/aps.54.3780
The electronic structure, dielectric functions, complex refractive indices and absorption spectra for the polarized light from the perfect PbWO4(PWO) crystal and the PWO crystal containing V2-Pb have been calcula ted using LAPW +LDA method with lattice structure optimized. The peaks of the absorpti on spectra corresponding to the electronic transitions have been studied. The op tical properties of PWO crystal containing V2-Pb are aniso trop ic. It may be caused by the anisotropy of lattice structure of the PWO crystal. Our calculated results indicate that the perfect PWO crystal does not have absor ption band in the visible and near_ultraviolet region, but the PWO crystal conta ining V2-Pb has absorption bands in visible and near_ultra viol et region. The absorption bands can be well decomposed into four Gaussian_shape bands peaking at about 350, 405, 550 and 670 nm. It predicates that these absor ption bands are related to the existence of the V2-Pb in t he PWO crystal.
2005, 54 (8): 3787-3792. doi: 10.7498/aps.54.3787
The structure of nanoscale lubricant films perfluoropolyether (PFPE) and its mob ility on a solid surface are important for the service durability and reliabilit y of the computer head_disk device. Molecular dynamic simulations based on a coa rse_grained bead_spring model are adopted to investigate the static properties s uch as molecular conformation, bead density, end bead density and the dynamic pr operties such as self_diffusion coefficient as a function of the wall effect and the functionality effect of PFPE films. The simulation results of static proper ties show that there is a monolayer in surface layer for nonpolar PFPE, while th ere is a complex layered structure for polar PFPE. While the simulation results of dynamic properties show that the diffusivity of PFPE films is enhanced by wal l effect but decreased by the functionality effect.
2005, 54 (8): 3793-3798. doi: 10.7498/aps.54.3793
Synchrotron radiation photoemission spectroscopy (SRPES) is used to study the in itial growth mode of the gold deposition on the surface of GaN, the Schottky bar rier height (SBH) and the electronic structure at the interface of the Au/GaN(00 01) system. The results show that at the initial stage chemical reaction exists between the Au and GaN substrate. Over the reaction layer, the growth mode of Au deposition is 3D island mode. The SBH is examined by the SRPES and the result i s 14eV, which is consistent with other experiment reports. Analyzing the ene rgy shift of valence band and the Au core level, the interface chemical reaction is confirmed. The theoretical calculation by linear augmented plane wave method gives the density of states. According to the calculation results, the principl e of the interface reaction is discussed.
The charge storage and its stability in corona charged polypropylene non-woven fabrics used as air filters
2005, 54 (8): 3799-3804. doi: 10.7498/aps.54.3799
The charge storage ability and its stability in polypropylene(PP) non_woven fabric electret used as an air filter material was discussed. The influence of tempe rature and environmental humidity on the charge stability was investigated. The role of material structure in the influence of humidity on charge stability was analyzed. It was found that the charge stability can be improved obviously by th ermal treatment, including aging after charging at room temperature and charging at elevated temperatures. Experimental results demonstrate that PP non_woven fa bric electret shows very good charge storage lifetime in ambient atmosphere. The transport of detrapped charge is controlled by the slow retrapping effect.
The light-stability of polycrystalline silicon films deposited at low temperatures from SiCl4/H2 mixture
2005, 54 (8): 3805-3809. doi: 10.7498/aps.54.3805
We have studied the stability of amorphous silicon and polycrystalline silicon films under illumination. These films are prepared by plasma-enhanced chemical vapor deposition technology from SiH4/H2 and SiCl4/H2 separately. The exp eriment indicates that the light-soaking degradation phenomenon, which exists in almost all amorphous silicon films, does not appear in the polycrystalline sili con films. The light-dark conductivity of polycrystalline silicon films does not decrease but increase during light irradiation. Furthermore, the variance of co nductivity depends on hydrogen dilution ratio. It is suggested that the persiste nt photoconductivity effect of polycrystalline silicon films may originate from the high crystallinity and the action of chlorine.
2005, 54 (8): 3810-3814. doi: 10.7498/aps.54.3810
In the inverted heterostructure photodiodes(IHPs), the strong polarization effect at the interface of the AlGaN/GaN heterostructure influences UV/Solar rejection ratios of this type of structure. In this paper, the total effect of polarization is divided into two parts: the polarization and dipole terms. Based on the model of GaN/AlGaN/GaN IHPs, the influence of dipoles on the UV/Solar rejection ratios is analyzed. The results show that when dipoles are considered, UV/Solar rejection ratios of photodetectors are about three orders of magnitude, which agree with the experiment of Tarsa. The influence of dipoles should be considered in the IHPs.
Electronic transport properties and simulation of random resistor network in granular mixture system of La0.7Ca0.3MnO3 and CeO 2
2005, 54 (8): 3815-3821. doi: 10.7498/aps.54.3815
Granular mixture samples were prepared with La0.7Ca0.3MnO 3(synthesized by solid reaction) and CeO2 mixed, pressed and sintered under different conditions. In resistivity versus temperature R(T) measurements, a metal-insulator transition was observed. R(T) data demonstrated that the sintering condition had a strong influence on the properties of the samples. A low sintering temperature had influence on the growth of small granules and their boundaries,a high-temperature and long-time sintering resulted in the formation of large granules. A random resistor network (RRN) model with a new iterative average method was used to simulate the transport property of the mixture samples. The simulation and experimental result in agreement. The result indicates that the RRN model is reasonable for understanding the electronic transport of the granular mixture samples consisting of La0.7Ca0.3MnO3 an d CeO2
2005, 54 (8): 3822-3830. doi: 10.7498/aps.54.3822
An ideal density of dangling bonds and the surface free energy (SFE) of (1×1)-(hkl) surface of cubic crystals are calculated by using a broken-bond model. The results show that the SFE(γ) can be expressed as γ=f(hkl)·(Eb/d2 0) where f(hkl) is a periodically convergent function, Eb and d0 are respectively the bond energy and the bond length. The f(hkl) is rela ted to the crystal structure. The anisotropy of the SFE and the equilibrium form (EF) of the crystal can be readily determined by using the results. It is found that the EFs of the crystals of fcc and bcc are truncated octahedron and rhombi c dodecahedron, respectively, which are coincident with the corresponding crysta ls' three dimensional first Brillouin zones, respectively.
2005, 54 (8): 3831-3838. doi: 10.7498/aps.54.3831
In this work, on the one hand, the contact-shadow-mask method and technique were used to micro-fabricate the magnetic tunnel junction (MTJ) and optimize the experimental conditions. The width of the gap for the long and narrow top or bottom magneto-electrode is 100 μm, which can be used to deposit MTJs and form a cross strip with the tunnel section of 100 μm×100 μm. The MTJs with tunneling magnetoresistance (TMR) ratio of 30%—48％ can be directly obtained for the structure of Ta(5 nm)/Cu(25 nm)/Ni79Fe21(5 nm)/Ir22Mn78(10 nm)/Co75Fe25(4 nm)/Al(08 nm)-O/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta(5 nm). On the other hand, t he MTJs with high TMR ratio and small active area from 20 μm×40 μm down to 4 μm×8 μm were fabricated using two optical lithography methods of milling contact hole and lift-off resist, combined with Ar ion-beam etching or CF4 reactive etching technique s. Then, the TMR ratio from 22% up to 50% can be achieved before and after annealing at around 300 ℃ for 1 h. Our investigation shows that the patterned MTJs, which were microfabricated using the two optical lithography methods stated above, can b e used as the fundamental element of magnetoresistive random access memory, magn etic read-heads in hard disk drives and the field sensitive sensor.
Effect of oxygen content on carrier localization and ion-cluster effect for the Fe-doped YBCO system
2005, 54 (8): 3839-3844. doi: 10.7498/aps.54.3839
The oxygen content, Hall coefficient and superconductivity are systematically studied on YBa2Cu3-xFexOy(x=00, 01 , 02) and YBa2Cu2.8Fe0.2Oy(y=705—653) systems. The results show that ox ygen content has a great influence on the transport and transfer of carriers and the superconductivity of the samples, the suppression of Tc caused b y Cu( 1) site substitution could be weakened by the increase of oxygen content to some extent. The carrier (holes) density in CuO2 plane plays a key role i n affecti ng the superconductivity. Based on the charge transfer model, and considering th e carrier localization and ion-cluster effect resulting from Fe substitution on Cu(1) site, we have discussed the change of carrier density caused by the oxygen content and Fe doping concentration. It proves that with the increase of Fe dop ing concentration or the decrease of oxygen content (for the same doping concent ration), the efficient oxygen vacancy increases, which enhances the ion-cluster effect and the carrier localization effect, resulting in the decrease of carrier density that participats in superconducting transport in the CuO2 pl ane, and accordingly, the decrease of Tc.
2005, 54 (8): 3845-3850. doi: 10.7498/aps.54.3845
We have measured the temperature dependence of thermal conductivity in the ab_plane as well as c_axis of a series of underdoped La2-xSrxCuO4 (x=0063, 0070, 0090, 0110, 0125) single crystals unde r ze ro and 14 T magnetic field. It is found that the thermal conductivity in both ab plane and c-axis are suppressed by the application of the magnetic fiel d parallel to the c-axis. Ｔhe temperature dependence of the thermal conduct ivity suppression is quite similar to the previously reported behavior of the an tiferromagnetic order induced by an applied magnetic field. We think that the fi eld_induced thermal conductivity suppression in ab plane is due to the elect ronic contribution, while along c-axis it is due to the phonon contribution. Both the suppressions of the thermal conductivity in ab plane and along c-axis probably originate from the field-enhanced charge and spin ordering.
2005, 54 (8): 3851-3855. doi: 10.7498/aps.54.3851
X-ray magnetic circular dichroism (XMCD) in the absorption of the single-crystal iron thin film deposited epitaxially on MgO substrate is studied to get the spin and orbital moment. The experiments show that along with different crystal axes, the change of orbital moment of Fe atoms is about 600%, the change of the spin moment is only about 50%, but the change of total moment is not so large. Researching the anisotropy by means of routine methods, the relation between the magnetic moment and the anisotropy of the thin film is studied.
Effect of the second-order magnetocrystalline anisotropic constant on the magnetization reversal in R2Fe14B magnets
2005, 54 (8): 3856-3861. doi: 10.7498/aps.54.3856
In this work, the dependence of the second-order magnetocrystalline anisotropic constant K2 on the minimum nucleation field Hminn has been investigated by the numerical method and the analytical formulation under the second-order approximation. It is found that the contribution of K2 t o H minn is very large at low temperatures for isotropic Pr2Fe14B magnets. Although the value of Hminn for Nd2Fe14B can b e obt ained using the analytical formulation under the first-order approximation, the value of Hminn for Pr2Fe14B is achie ved using the formulation under the second-order approxiamtion. Using the obtained value of Hminn, a good linear relation between coercivity and Hminn is found in the temperature range from 20 K to room temperature.
2005, 54 (8): 3862-3866. doi: 10.7498/aps.54.3862
Amorphous Fe89.7P10.3 alloy nanowire arrays were fabri cated in an anodic aluminum oxide template by means of electrodeposition. X-ray diffract ion, transmission electron microscopy, vibrating sample magnetometer and Mssbauer spectrometer are employed to study the structure and magnetic properties of the nanowire arrays. The results show that the nanowire arrays are amorphous with a perpendicular magnetic anisotropy and high coercivity Hc=304 ×104 A/m. The mean hyperfine field and the mean isomer shift of the insi de of nanowires are 215×106 A/m and 007 mm/s, respectively. The mean hype rfine field (233×106 A/m) at the end of nanowires is higher than that of th e inside of nanowires, but the mean isomer shift (004 mm/s) at the end of nanowires is smaller than that of the inside of nanowires. The average angle between the Fe magentic moment and the wire axis is 16° in the the inside of nanowires, but the average angle is 28° at the end of nanowires. Due to the shape anisotropy of nanowires, the ordered alignment of magnetic moments is realized in the disordered amorphous alloy system.
Structure and magnetic properties of FePt/Ag nano-granular films with perpendicular magnetic anisotropy
2005, 54 (8): 3867-3871. doi: 10.7498/aps.54.3867
［FePt 2 nm/Ag d nm］10 (d=0—11) multilayers were prepared on single crystal MgO(100) substrates kept at room temperature and 250 ℃ by means of magnetosputtering. L10-FePt/Ag granular films with perpendicular magn etic anis otropy and high coercivity have been obtained after vacuum annealing the multila yers deposited on substrates kept at 250 ℃ for 15 min. X-ray diffraction result s indicate that FePt particles have a strong ［001］ orientation. The size of Fe Pt particles decreases with the increase of the thickness of Ag layer. After vac uum annealing the ［FePt 2 nm/Ag 9 nm］10 films at 600 ℃ for 15 min, FePt /Ag granular films are obtained with only 8 nm of particle size and 692 kA/m of coercivity. Isothermal magnetization remanence and dc-demagnetization remanence measurements show that no magnetic exchange coupling between magnetic particles can be observed. Such a kind of films is suitable for future ultra-density perp endicular magnetic recording medium.
2005, 54 (8): 3872-3877. doi: 10.7498/aps.54.3872
The great magnetoelectric(ME) effect is a product property of the composite consisting of individual piezoelectric and magnetostrictive phases. The TbDyFe/PZT laminate composites were prepared by magnetron sputtering, and the ME coefficients αE were examined experimentally and calculated by using a finite e lement analysis software. Results showed that the experimental data were in agreement with the calculated results and the value of αE reached the maxim um at the resonance frequency, and αE increased with the increase of the magnetostricive thickness.
2005, 54 (8): 3878-3883. doi: 10.7498/aps.54.3878
A carbon nanotube/polyaniline composite nanotube with a diameter of 50—80 nm has been prepared. The carbon nanotubes encapsulated by polyaniline (PANI) with a thickness of 20—30 nm have been synthesized by in-situ emulsion polymerization. The microwave permittivity of the carbon nanotube/polyaniline composite nanotubes has been investigated in the frequency range of 2—18 GHz. The real part (ε′) and imaginary part (ε″) of the complex permittivity of carbon nanotube/polyaniline composite nanotube change little, as compared with those of carbon nanotubes at frequencies 2—18 GHz. The ε′ and ε″ of the carbon nanotube/polyaniline composite nanotube are small at low frequencies, which make it easy to match the impedance of free-space in the design of microwave absorbing materials. The dissipation factor tanδ(ε″/ε′) of carbon nanotube/polyaniline composite nanotube is high. So the carbon nanotube/polyaniline composite nanotube is a good microwave absorbent.
2005, 54 (8): 3884-3888. doi: 10.7498/aps.54.3884
The conduction mechanism of ultra-thin gate oxide n-metal-oxide-semiconductor fi eld effect transistor (n-MOSFET) after soft breakdown is studied in this paper. It is found that in a certain range of gate voltage Vg, the gate cur r ent Ig follows the Fowler-Nordheim-like tunneling mechanism, and the experimen tal tunneling barrier b is 0936 eV in average, which is much smal ler t han the interface barrier of Si/SiO2 We think that after soft brea kdown, the electrons existing in the quantization energy levels of the Si/SiO2 interface , not directly tunnel to the oxide conduction band, but tunnel to the oxide defe ct band. b is determined by both the defect band energy level and t he qu antization energy level of the tunneling electrons. With rising experimental tem perature, the tunneling of high energy level electron is also increasing, which reduces b gradually.
Design of wide-angle and broad-band two-dimensional photonic crystal polarization splitter by the automatic shaping mechanism
2005, 54 (8): 3889-3893. doi: 10.7498/aps.54.3889
Based on the mechanism of automatic shaping, the corrugated multilayer films of two_dimensional (2D) phtonic crystal is designed.This structure realizes omnidirectional polarization splitting with TM mode passing window between λ＝148 and 152μm, which is the complete band gap of TE mode. The variable rang es of the slope angle of the layers and the width of a-Si single layer are 38° —49° and 014—015μm, respectively. Band structure has been used to expl ain the omnidirectional polarization effect. An arrow-end_like 2D photonic cryst al which is the deformation of the corrugated multilayer films is introduced for comparison. It can only work as a wide-angle polarization splitter not as an o mnidirectional one for wavelength from 128 to 131μm. The comparison of th e band structures of these two different 2D photonic crystals leads to the metho d of extending the incident angle of polarization splitter.
2005, 54 (8): 3894-3899. doi: 10.7498/aps.54.3894
The fluorescence properties of Er3+:4I13/2→4I15/2 transition in tellurite glasses have been investigated as a f u nction of the Er3+ concentration. The critical distance R0 for whic h concentration quenching will happen, and the interaction microparameter C Er-Er in tellurite glasses were determined on the basis of the energy migr ation model of Dexter theory. The value of CEr-Er in the proposed tel lurite glass was compared with that in other glass hosts. Finally, the concentration quenching mechanism described using a model based on energy transfer and quenching by hydroxyl groups was presented.
Optical properties of Bi3.25La0.75Ti3O12 and Bi3.25Nd0.75Ti3O12 thin films prepared by a chemical solution method
2005, 54 (8): 3900-3904. doi: 10.7498/aps.54.3900
The optical properties of Bi3.25La0.75Ti3O 12 (BLT) and Bi 3.25Nd0.75Ti3O12 (BNT) thin films de posited on (111)Pt/Ti/ SiO2/Si substrates by a chemical solution method were investigated. B oth BLT a nd BNT thin films showed single phase of bismuth-layered structure. The BNT fil m composed of the homogeneous and large rod-like grains, while the grains in BLT film were small. The optical constants (refractive index and extinction coeffic ient) in the wavelength range of 200—1700nm and the thickness of the films we re obtained by spectroscopic ellipsometry measurements. The optical band gaps o f BLT and BNT were estimated to be 430 and 361eV, respectively. The disper sion of the refractive index in the interband transition region was analyzed by using the single electronic oscillator model.
2005, 54 (8): 3905-3909. doi: 10.7498/aps.54.3905
In this work, the abnormal double-peak in the electroluminescence spectra of In xGa1-xN/GaN multiple quantum wells (MQWs) light emitting d iode s tructure materials with high indium contents was studied under different injecti on currents. The results show that the screening of internal electric field by i njection current plays an important role in the radiation recombination process of InxGa1-xN/GaN-MQWs materials.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2005, 54 (8): 3910-3914. doi: 10.7498/aps.54.3910
A series of microcrystalline silicon thin films were fabricated by very high frequency plasma-enhanced chemical vapor deposition at different substrate temperat ures (Ts). Analysis of materials structure was conducted using Fourie r tra nsform infrared (FTIR). The results showed that hydrogen content of the samples decreased with the increase of Ts. The results of FTIR and secondary ion m ass spectra indicated that the oxygen content of the samples increased with the increase of Ts. Compared with those at higher Ts, samples prepared at low Ts easily adsorbed oxygen, and showed bad stability.
Target ablation characteristics of thin films during nanosecond pulsed laser deposition in the ablation process
2005, 54 (8): 3915-3921. doi: 10.7498/aps.54.3915
The whole ablation process of target during the pulsed laser preparation of thin films is studied in this paper. An ablation model of targets in which the vapo rization is taken account is present based on the superheated theory. Different heat flux equations for different stages are then established. Finally, as usin g Si as the target, a finite difference method is employed to simulate the space _ and time_dependence of temperature in the target. Vaporization velocity and va porization thickness evolutions with different laser fluence are investigated. T he dependence of solid_liquid interface location S(t) on time which takes in to account the melting relaxation time is derived too. The results show that th e vaporization strongly affects the surface temperature in the pulsed laser abla tion. When the laser intensity reaches near the phase explosion energy threshold , the vaporization velocity and ablation depth will evidently decrease because o f the gas dynamic effects. This result is more appropriate than that obtained in previous works.
2005, 54 (8): 3922-3926. doi: 10.7498/aps.54.3922
Based on the extended two-dimensional Su_Schrieffer_Heeger model of polythiophene, we have studied numerically the pinning effects of the Coulumb interaction o n the localized vibrational modes around a bipolaron in polythionphene. Some new localized vibrational modes are found. The numerical results are almost in good agreement with the results of optical absorption experiments.
2005, 54 (8): 3927-3934. doi: 10.7498/aps.54.3927
Face-center cubic metal materials including austenite stainless steel, aluminum single crystal and multi-grained pure aluminum were irradiated by a high-current pulsed electron beam (HCPEB) source in different processes. The deformed microstructures were observed by using scanning electron microscopy and transmiss ion electron microscopy. The relationship between stress characteristic and the microstructures has been analyzed. The current numerical simulations of the ther mal-mechanical process of HCPEB treatment were also investigated by comparing w ith the present experimental results. The present experimental results suggest t hat the value of the stress induced by HCPEB lies between 102—103MPa. The behavior of the stress propagation is closely related to the crystal structure of the material. This stress leads to the modification of the properties and the microstructures of the irradiated material in regions of greater depth.
Field emission properties of diamond-like carbon and carbon nitride films deposited by the electrochemical method
2005, 54 (8): 3935-3939. doi: 10.7498/aps.54.3935
Diamond-like carbon (DLC) and carbon nitride (CNx) films were deposit ed successfully by the electrochemical method.The conditions of deposition were discussed also.Scanning electron microscope and Fourier transform infrared technigue were used to investigate the surface morphology and the bonding structure.The results of the field emission show that the turn-on fields of DLC films and CNx films are 88 and 10V/μm respectively.Under the field of 23V/μm,their current densities are as high as 10 and 037 mA/cm2, respectively .
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2005, 54 (8): 3940-3946. doi: 10.7498/aps.54.3940
The complexity series of the logistic equation and the Lorenz model were respectively calculated using a dynamical nonlinear analysis method for time series— —Lemper-Ziv complexity algorithm, and the physical implication of Lemper-Ziv co mplexity is also discussed. Results show that for the logistic equation, the com plexity is obviously different when the complicated degree of the time series i s variational; and for Lorenz model, i.e. its x-, y-, and z-portions, th eir complexities are all chaotic and are all composed of many cycles whose swings are almost the same and the lengths are different. The result reflects the in ternal quasi-periodicity. Further investigations indicate that when different wi ndow lengths are selected, the characters of the complexity series for a given t ime series are basically the same, and there exists a coherency between the jump s of the complexity series and the jumps of the time series. Thus one can judge the characteristic of a time series by calculating its complexity. This may be u seful to predict the kinetic behavior of a time series.
On the difference between empirical mode decomposition and wavelet decomposition in the nonlinear time series
2005, 54 (8): 3947-3957. doi: 10.7498/aps.54.3947
The method of empirical mode decomposition （EMD） based Hilbert transformation is that separate the nonlinear time series into intrinsic mode functions （IMFs ） with different time scale by using EMD, then apply the Hilbert transformation to every IMF to get the Hilbert spectrum.By systematically comparing the advan tages and disadvantages between EMD and wavelet decomposition （WD）, between Hi lbert transformation and wavelet transformation in transacting nonlinear time s eries using ideal time series and 18O time series of Guliya i ce co re on the Tibetan Plateau, we present some improving measures to reduce the di sadvantages. The result of investigation show that the combination of EMD-based and WD-based methods may be more effectively in recognizing the main informatio n of the time series.
2005, 54 (8): 3958-3961. doi: 10.7498/aps.54.3958
Kerr black hole has only two parameters of M and J. M and J, as the general coordinates, together with their conjugate variables form a four-di mensional phase space. The quantum area spectrum of Kerr black hole is obtained by performing gauge transformations, from which we can obtain the smallest mas s of Schwarzchild black hole.
2005, 54 (8): 3962-3966. doi: 10.7498/aps.54.3962
The effects of the dangling end on the electronic transport properties of the single-wall carbon nanotubes (CNTs) have been investigated, based on the tight-binding model and Landau formula. It is found that the conductance oscillates per iodically near the Fermi energy in the CNT with a finite-length open dangling en d. Both slow and rapid oscillations occur in armchair CNTs, but only the rapid o scillation appears in zigzag ones. The period of the rapid oscillation decreases with increasing the length of the dangling end. Moreover, the mean conductance of the CNTs with finite-length open dangling end is about twice as that with inf inite-length open dangling end. Some relevant application is also discussed.