Vol. 53, No. 2 (2004)
2004, 53 (2): 325-330. doi: 10.7498/aps.53.325
In this paper, the uncertainty of an uncertain singular system is described in the viewpoint of a system family. The concept of `generalized quadratic stable cone' is proposed. In terms of matrix inequalities, the necessary and sufficient conditions are derived, under which the considered uncertain system is generalized quadratic stable/stabilizable one.
2004, 53 (2): 331-336. doi: 10.7498/aps.53.331
In this paper, we study the form invariance of a mechanical system with unilateral holonomic constraints. According to the invariance of the form of the differential equation of motion under the infinitesimal transformations, we give the definition and criterion for the form invariance of mechanical systems with unilateral holonomic constraints, and establish the relation between the form invariance and Noether symmetry and Lie symmetry. In the end of the paper, an example is given to illustrate the application of the results.
2004, 53 (2): 337-342. doi: 10.7498/aps.53.337
For the relative rotation dynamic equation of the cylinder between random twain cross sections, we gain an analytic solution for the equation by using the coupling method. Due to the particularity of the equation, we gain an invertible matrix by utilizing the Jordan canonical. Thereby, we obtain an integral solution for the relative rotation dynamic equation of the cylinder. According to the reguirements in engineering applications, we give some analytic solutions of two types of load action, i.e.the impact and periodic types.
2004, 53 (2): 343-348. doi: 10.7498/aps.53.343
From the definition of Legendre elliptic integration and Jacobi elliptic function, new transformations are obtained and applied to construct the exact solutions of nonlinear wave equations. The nonlinear Klein-Gordon equation, Boussinesq equation and the coupled mKdV equations are taken as three examples to illustrate the detailed steps in obtaining exact solutions. There new analytical solutions such as periodic solutions and soliton solutions are derived for these nonlinear evolution equation (or equations).
2004, 53 (2): 349-355. doi: 10.7498/aps.53.349
By use of the extended mapping deformation method,many explicit and exact travelling wave solutions of the two newly generalized Ito systems are obtained which contain solitary wave solutions,trigonometric function solutions,Jacobian elliptic function solutions and rational solutions.
2004, 53 (2): 356-361. doi: 10.7498/aps.53.356
Within the frame of the ABCD formulation for the propagators in a time-dependent quantum system, the ABCD law has been extended to the so-called effective ABCD system in which the effective beam quality factor is conservative. We discussed the system as the propagation of the atom laser beam. The effective beam quality factor and the effective parameter are introduced to obtain the effective ABCD formulation of the propagators by means of Heisenberg picture. The atom-atom interactions in the atom laser beam make the beam quality factor nonconservative, and thus the effective beam quality factor can describe the combined effect of the beam quality factor and the atom-atom interaction.
2004, 53 (2): 362-366. doi: 10.7498/aps.53.362
By using the method of quantum statistics,we directly derive the partition functions of the bosonic field and fermionic field in the Sen black hole with an axial symmetry.Then via the improved brick-wall method and the membrane model,we calculate the entropies for the bosonic field and fermionic feld.We derive the entropy of the black hole which is not only related to the area of the outer horizon but also the function of the area of the inner horizon.In our results, there are no logarithmic divergent terms and left terms.There does not exist the question why the entropy of the scalar field or Dirac field outside the horizon is the entropy of the black hole.The influence of the spinning degeneracy of particles on the entropy of a black hole is studied.When the radiation temperature of the black hole approaches absolute zero,the entropy determined by the area of the inner and outer horizons also approaches zero.This satisfies the Nernst theorem.It can be taken as the Planck absolute entropy of a black hole.
Under the flat Minkowski space-time background,in the harmonic and the arbitrary coordinate systems,we obtained the graviton free propagators in the n-dimensional general relativity (GR) and the high derivative gravity respectively,calculated the expressions of the leading terms of several two-point curvature vacuum correlation functions,and proved that they are zero in the GR,but in the high derivative gravity they are not zero.
The long-range correlation of nodes in a computer network model is studied with the mean square fluctuation function of cumulative variable of queue lengths. It is shown that the queue lengths of the data packets of nodes change their temporal independence on or short-range correlation in the free flow state to long-range correlation in the critical and congested state with increasing system loading. The range of correlation enlarges and the collective long-range correlation emerges. In a free flow, the nodes are independent of each other or short-range correlative, and there exists a typical characteristic power exponent of 0.5. At the critical state, the nodes are long-range correlative, and there exists a typical characteristic power exponent bigger than 0.5. Moreover, the collective interaction becomes obvious and the power exponent decreases with enlarging network scale.
2004, 53 (2): 379-382. doi: 10.7498/aps.53.379
Synchronization of two chaotic systems with different parameters using the random parametric adaptive control algorithm is proposed. Under the appropriate control law and feedback coefficient, the synchronization is achieved. To make this method realizable, Henon map is taken as a typical numerical example. The characteristic of random control period and flexible feedback coefficient shows its practicality.
2004, 53 (2): 383-387. doi: 10.7498/aps.53.383
A special kicked rotor moving in a piecewise continuous force field is suggested and studied. When adjusting a control parameter,the rotor displays a transition from conservative to quasi-dissipative, and a change of a stochastic web formed by the set of the images of the discontinuous borderlines to a transient stochastic web. This transition and change can be described by a logarithmic rule of the fractal dimension of the transient stochastic web versus the control parameter, or a rule of the averaged lifetime of the iterations in the transient stochastic web versus the control parameter.
2004, 53 (2): 388-395. doi: 10.7498/aps.53.388
Based on a dynamics research of the typical Langevin problem, i.e., a moving charged particle under the continuous influence of a constant impulse in a double-well potential and a time-dependent magnetic field, using the stroboscopic sampling, we propose complex difference equations which can describe the change rule of particle's velocity. By selecting appropriate magnetic intensity and time intervals (sampling period), we reduce the difference equations to complex mapping which is used to construct the generalized M-J sets. Based on the particle's dynamics characteristic, we discussed the physical meaning of the generalized M-J sets. The authors found that: (1) The fractal structure of the generalized M-J sets may visually reflect the change rule of particle's velocity. (2) Whether the selected time intervals is significative determines whether the fractal structure of the generalized M-J sets has the continuity. (3) The evolution of the generalized M-J sets, i.e., the change rule of particle's velocity, depends on the different choices of the principal range of the phase angle. (4) If we change the choices of the magnetic intensity and time intervals, for example, choose a random fluctuant magnetic field, the generalized J sets may present the interior-filling structure feature, i.e., “explosion" phenomena appear in the closure of the particle's instable periodic orbits in the velocity space.
2004, 53 (2): 396-400. doi: 10.7498/aps.53.396
We study numerically the effect of signal modulating noise in bistable stochastic dynamical systems. By making a numerical analysis of the bistable stochastic dynamical systems, we find that the effect of an input sinusoidal signal is also a sinusoidal signal in the output, and the effect of the white noise is a Wiener process. When the system parameters are small enough, the coupling effect between the sinusoidal signal and the white noise can be largely weakened. Under this condition the noise can be largely reduced in the system output, and the effect of signal modulating noise can occur in the bistable stochastic dynamical systems.
2004, 53 (2): 401-405. doi: 10.7498/aps.53.401
The thermal conductivity, emissivity, specific heat capacity and thermal diffusivity of SiNx thin films which are widely used in semiconductor and microelectronics MEMS are measured using a novel experimental method which combines the heater and the bolometer in one unit. The obtained reliable thermal properties are very useful for microelectronic circuits design and mask processing. The experimental data show that the thermal conductivity, emissivity and thermal diffusivity of SiNx thin films are much lower than those of the bulk and depend on the temperature and thickness of the thin films, and the size effect of SiNx thin films is notable. However, the specific heat capacity of SiNx thin films is almost the same as that of the bulk.
Preliminary research results for generation and application of high power ion beams on FLASH II accelerator
2004, 53 (2): 406-412. doi: 10.7498/aps.53.406
Preliminary results for the generation and application of the high power ion beam(HPIB) on the FLASH Ⅱ accelerator are reported. The structure and principle of the pinch reflex ion beam diode are introduced. The equation of parapotential flow is corrected for the reduction of diode A-K gap due to the motion of cathode and anode plasma. The HPIB peak current of ～160kA is obtained with a peak energy of ～500keV. Experimental investigations of generating 6—7MeV quasi-monoenergetic pulsed γ-rays with high power ion(proton) beams striking 19F target are presented. In addition, the results of the thermal-mechanical effects on the material irradiated with HPIB, which are applied to the simulation of 1keV black body radiation x-rays, are also discussed.
ATOMIC AND MOLECULAR PHYSICS
2004, 53 (2): 413-417. doi: 10.7498/aps.53.413
The twisted stigmatic beam with an orbital angular momentum was generated by transforming the Hermitian-Gaussian beam of a laser-diode-pumped solid-state laser through a rotated cylindrical lens system. By utilizing the orbital angular momentum of the generated beam, an “optical spanner” was designed and developed. By using the optical spanner micro-sized particles were trapped and rotated.
2004, 53 (2): 418-422. doi: 10.7498/aps.53.418
The dependence of molecular ionic spectral intensity on the pressure of mother molecules in velocity modulation spectroscopy was experimentally and theoretically studied. A new diagnosis of some plasma parameters, e.g. electric field, electron temperature and ionized coefficient, was proposed and carried out.
2004, 53 (2): 423-426. doi: 10.7498/aps.53.423
Algebraic Hamiltonian of tetratomic molecules is classified using the coherent state.The potential energy surface is derived from the classical Hamiltonian. We proposed a new transformation for introducing the bond angles to the potential energy surface. We have calculated the dissociation energy and the force constants. These results are in good agreement with previous results.
CLASSICAL AREA OF PHENOMENOLOGY
Green's function method of light scattering from random surfaces compares with Kirchhoff's approximation
2004, 53 (2): 427-435. doi: 10.7498/aps.53.427
Starting from the Helmholtz Equation, we obtain the integral equations of the light field at the medium interfaces by use of Green's theorem. Then the integral equations are discretized into a linear equation set, from which the values of the light field and its derivatives at the interface can be numerically solved. We also obtain the expression for the transmissive light waves from the Green's-function integral in the case of Kirchhoff's approximation. By an analogy to the derivation process of the autocorrelation functions of speckles in Frauhofer plane, we propose the method for the generation of random self-affine fractal surfaces and Fourier transformation method for the numerical derivative of random surfaces. Then we study the accuracy of Kirchhoff's approximation in the scattering of light field from the random self-affine fractal surface. We find that the accuracy of Kirchhoff's approximation is relatively high when the root-mean-square roughness w is small. for random surfaces with the same value of w but smaller values of roughness exponent α, the Kirchhoff's approximation gives higher accuracy in the calculation of scattered light fields. We believe that the results of this paper would be of significance in understanding the validity range of the Kirchhoff's approximation when it is applied to light scattering from self-affine random surfaces.
2004, 53 (2): 436-440. doi: 10.7498/aps.53.436
Using a microlens array to focus an amplified femtosecond laser pulse inside a bulk PMMA(polymethyl methacrylate), optical breakdown occurs at each focus of the microlenses. By changing the positions of the foci,we realize the three-dimensional optical recording of high contrast bits at a speed of 20Mbit/s (with a 1kHz fs pulse laser ) in PMMA. Accordingly, modulation and readout of binary data have been presented. The diameter, focus length,and lens aberration in the microlenses are key factors which affect the recording speed and optical capacity based on this mechanism. Two kinds of effective ways to increase the capacity are discussed in this paper.
Teleporting superpositions of even and odd coherent states of a cavity field via the entangled state of a degenerate Λ-type atom interacting with the cavity field
2004, 53 (2): 441-444. doi: 10.7498/aps.53.441
Based on the modified effective Hamiltonian for the system which is made up of a degenerate Λ-type three-level atom and a single-mode coherent state cavity field,the wave function of the system for the arbitrary initial states is derived by means of matrix forms. Through changing the interaction time,the entangled state of an atom-field is prepared. A feasible scheme is proposed to probabilistically teleport superpositions of even and odd coherent states of the cavity field by using the entangled state of a degenerate Λ-type three-level atom interacting with a coherent state cavity field of large amplitude under a far-off resonant condition. By performing Bell state measurement, the superpositions of even and odd coherent states of the cavity field can be successfully achieved with a total probability of 0.25.
2004, 53 (2): 445-449. doi: 10.7498/aps.53.445
A systematic investigation was made for the R—M transition and recombination lasers in strontium ions by the longitudinal pulse discharge-excited with the helium buffer gas in a quartz discharge tube of 9mm inner diameter and 42cm electrode's separation. The laser power of each-line as a function of different working parameters,as well as the corresponding photo-electrical pulse waveforms were analyzed and observed for two kinds of optical cavity. A set of better operating parameters was also obtained for the multi-line strontium ion laser.
Thermal background suppression in Rayleigh-type nondegenerate four-wave mixing based on field-correlation effects
2004, 53 (2): 450-455. doi: 10.7498/aps.53.450
We apply the principle of field-correlation to the thermal background suppression of the Rayleigh-type nondegenerate four-wave mixing spectra,which have been employed for the measurement of ultrafast longitudinal time in the frequency-domain recently. Conditions,under which contributions from the thermal grating can be neglected,are given and numerical results that illustrate the validity of this method are presented.
Experimental research on gain characteristics and nonlinear effect of dispersion compensation Raman amplifiers
2004, 53 (2): 456-460. doi: 10.7498/aps.53.456
Discrete dispersion compensation Raman amplifiers (DCRA) are recently used in dense wavelength division multiplexing (DWDM) systems for compensating for both dispersion and fiber loss simultaneously. In this paper,the gain spectrum,gain saturation and the effect of stimulated Brillouin scattering (SBS) of DCRA have been experimentally investigated.
2004, 53 (2): 461-467. doi: 10.7498/aps.53.461
We have observed an effect of light-induced refractive index change in LiNbO3∶Fe crystal sheet,which is different from the photorefractive effect. It has the characters of faster response (<0.1s),isotropy and function of information storage. We have also discussed the physical mechanism of the effect.
The influences of seed on stimulated Brillouin scattering pulse shape fidelity in seeded single-cell
2004, 53 (2): 468-472. doi: 10.7498/aps.53.468
To seed a Stokes pulse into the stimulated Brillouin seattering(SBS) generator, the induced SBS by this seeded Stokes pulse can make the SBS threshold reduced, and the best shape fidelity can be obtained. The influences of seed power on SBS pulse-shape fidelity in a seeded single-cell are investigated in theory and experiment.
2004, 53 (2): 473-477. doi: 10.7498/aps.53.473
In this paper the evolvement of the filamentation of femtosecond laser pulses propagating in air is studied experimentally.We observed the variation of light intensity in the beam profile and the interaction of the filament with the distribution of light intensity in the forming of the plasma filament by using imaging.The experimental results show that the laser pulse propagating in air first forms two filaments and then merges into a single filament.The numerical simulation using the nonlinear Schrdinger equation coupled to a multiphoton ionization law appears to describe several experimental results quite well.
2004, 53 (2): 478-483. doi: 10.7498/aps.53.478
It Is reported that the supercontinuum spectrum can be generated in holey microstructure fibers by femtosecond laser pulses with a 800nm center wavelength. Broadband continua extending from 440 to 890nm are generated in holey microstructure fibers. Based on the theory of scalar approximation, the effective refractive index of the cladding and effective area for the fundamental space-filling mode and chromatic dispersion of fibers are calculated. It is found that the holey microstructure fibers have specifically the ability of controlling dispersion and waveguide property.The mechanism of supercontinuum generation in holey microstructure fibers is explicated preliminarily. The theoretic analysis is in good accodance with the experimental result.It is considered that supercontinuum broadband spectrum can be generated in holey microstructure fibers even if their cladding constitutes of random gas-line.
2004, 53 (2): 484-489. doi: 10.7498/aps.53.484
A novel model for light propagation in elliptical-hole photonic crystal fibers (PCFs) is developed in terms of orthogonal function model. A new method for constructing supercell lattice is proposed; with this method the transverse index profile is decomposed into two periodic structures, and the mode field is decomposed using Hermite-Gaussian functions. The propagation constant and the mode field distribution of the PCF can be calculated by recasting the Maxwell equations into on eigenvalue system. With this model, the mode properties including dispersion properties, polarization properties and mode area can be analyzed for circular or elliptical hole PCF.
Studies on the amplified picosecond optical pulse by semiconductor light amplifiers using an improved model
2004, 53 (2): 490-493. doi: 10.7498/aps.53.490
After presenting an improved theoretical model that describes the dynamic process of optical pulses amplification by the semiconductor light amplifiers (SLAs), both the rising and falling time of amplified picosecond optical pulses by the SLAs have been investigated numerically. The results show that with the increase of the bias current of SLAs, the rising time will decrease and the falling time increase; the input pulse with a large peak power will accelerate the rising time shortening and the falling time lengthening; the gain compression has an obvious influence on the rising and falling time for several picosecond-width input pulses and gives approximately no effect on the input pulses in the tens of picosecond range; the gain asymmetry and shift strongly affect the rising and falling times.
2004, 53 (2): 494-497. doi: 10.7498/aps.53.494
A theoretical method of in-fiber Bragg grating temperature sensing has been proposed. Based on a temperature sensing model of in-fiber Bragg gratings, it was deduced that the analytical formulae of first-order and second-order and effective linear sensitivity coefficients of in-fiber Bragg grating temperature sensing. The theoretical values of each sensitivity coefficient was calculated. Conic multinomial has been obtained by experiment. The results of theory and experiment were compared and analyzed. Furthermore, the influence of quartzose mechanical parameters on temperature sensing characters of in-fiber Bragg gratings and the application range of linear and nonlinear relations of reflected wavelength versus temperature were also discussed.
Assembly prestress and its variation in different water depths when applied to the active elements of a flextensional transducer
2004, 53 (2): 498-502. doi: 10.7498/aps.53.498
It is very important for underwater flextensional transducers to accurately control the prestress applied to the active element in assembling and working process, especially, for the rare-earth magnetostrictive flextensional transducer, to be investigated clearly the relationship between the working in different water depths and the compressive prestress applied to the active element,which will be conducive to employ the active element potential energy. On coordination with the author's research project, the assembly displacement of an underwater flextensional transducer, by which is applied prestress to the active element, is calculated with the finite element method, and an elementary experiment is performed with a class VII flextensional transducer. The magnitudes of compressive prestress is variable when working in different water depths, the relationship is calculated by using finite element method(FEM).The method used in this paper may be generalized to other kinds of flextensional transducer.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Preparation of titanium nitride films by pulsed high-energy-density plasma and investigation of the tribological behavior of the film
2004, 53 (2): 503-507. doi: 10.7498/aps.53.503
Supper hard and wear resistant titanium nitride films were deposited onto 0.45% carbon steel substrate by pulsed high-energy-density plasma(PHEDP) technique at ambient temperature. The microstructure, surface compositions and depth profile of the film were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM).The hardness profile and tribological behavior of the film were determined with nano-indenter and MM200 wear tester, respectively. The results showed that the microstructure of the film was dense and uniform and mainly composed of titanium nitride phases. A wide mixing interface existed between the film and the substrate. The film possessed a very high value of nanohardness. The wear resistance of the film was excellent and the value of the friction coefficient of the film was low under dry sliding wear test conditions.
2004, 53 (2): 508-513. doi: 10.7498/aps.53.508
Extending the propagation formula of the attenuated laser-induced plasma shock wave front with spherical symmestry in the air to the non-absolute centric symmetry is described in this paper. According to the analysis of the measured data for the laser-induced plasma shock wave front by using photo shadowgraph, a propagation formula of a rotational ellipsoid shock wave for a point source in the laser-induced plasma in a liquid is presented in this paper.The shock wave attenuation in pure water and ethanol has been investigated by means of the acoustic method. The experimental data are in agreement with the calculated results.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
X-ray absorption fine structure and x-ray diffraction studies on structures of Fe70Cu30 alloys affected by mechanical alloying
2004, 53 (2): 514-520. doi: 10.7498/aps.53.514
The XAFS and XRD techniques were used to study the local structure changes around Fe and Cu atoms in the mechanical alloying (MA) Fe70Cu30 with the milling times. At the initial MA stage milling for 2 hours, the Cu fcc lattice in Fe70Cu30 mixture is largely distorted, and the disorder factor σ(σ=σT+σS) of Cu atoms is about 0.0190 nm. After being milled for 5 hours, part of the Cu atoms located at the grain boundaries diffuses into the bcc lattice of the α-Fe phase, which makes the average disorder factor σ around Cu atoms decrease to 0.0108 nm. When the milling time reaches 10 hours, most of the Fe atoms are in the fcc Fe-Cu phase whose disorder factor σ is about 0.0119 nm, while the local structures of Cu atoms mainly maintain fcc structure, and the σ around the Cu atoms is about 0.0110 nm. We consider that the bcc structural Fe-Cu phase might be induced into the fcc structure by Cu atoms, when the concentration of Cu atoms incorporated into the bcc Fe-Cu phase is increased to about 30%—40%. The XAFS result of the Fe70Cu30 milled for 20 hours is similar to that of the Fe70Cu30 milled for 10 hours. The final MA product is composed of two phases: Fe80Cu20-like bcc structure and Fe60Cu40-like fcc structure.
With the method of LEED graphic fitting, we have made a thorough study on the stability and faceting of In/Si surfaces. As a result, three new In/Si stable surfaces with less than 0.5 ML coverage ,that is, Si(2 1 4)-In, Si(3 1 7)-In and Si(4 3 6)-In and two In/Si stable surfaces with about 1ML coverage, that is, Si(1 0 1)-In and Si(3 1 3)-In, have been found. Meanwhile, the family territories of total 4 In/Si stable surfaces with less than 0.5 ML coverage and 6 with about 1ML coverage have been roughly determined. Particulaty, the family territory of Si(1 0 3)-In is rather big, even a little bigger than that of Si(1 1 1)-In.
2004, 53 (2): 527-530. doi: 10.7498/aps.53.527
We have studied analytically the electron effective mass of single-wall carbon nanotubes. The relation between the effective mass of electrons at the bottom of lowest-lying conduction band and the tube diameter and chirality has been discussed. It is shown that geometrical structures have very important effect on the electron effective mass of single-wall carbon nanotubes.
2004, 53 (2): 531-536. doi: 10.7498/aps.53.531
After being modified and dispersed uniformly in solution, the Ni-P-carbon nanotube composite coatings are prepared by chemical deposition. The surface morphologies of composite coatings are analyzed with a scanning electron microscope and the tribological properties of composite coatings are investigated. The results indicated that the addition of carbon nanotubes increased the microhardness and improved mechanical properties of the Ni-P composite coating significantly. Carbon nanotubes composite coatings exhibited lower friction coefficient and high wear resistance in comparison with Ni-P-SiC composite coatings.
Effect of density on the thermoelectric properties of the filled skutterudite compound La0.75Fe3CoSb12
2004, 53 (2): 537-542. doi: 10.7498/aps.53.537
The effect of density on the thermoelectric properties of the filled skutterudite compound La0.75Fe3CoSb12 was investigated. The La0.75Fe3CoSb12 showed p-type conduction. The mobility increased with an increase in density. The electrical resistivity increased and the thermal conductivity decreased with decreasing density due to the pores scattering. The Seebeck coefficient is independent of density. The portion of electrical resistivity increase is consistent with that of the thermal conductivity reduction. The value of ZT of the specimen with low density is compared to that of specimen with high density. The value of ZT does not depend on density.
2004, 53 (2): 543-549. doi: 10.7498/aps.53.543
The influence of doping with different trivalent ions (La3+，Y3+，Bi3+，Sb3+)on the properties of lead tungstate crystals (PWO) has been investigated. Transmission, emission, positron annihilation lifetime and x-ray photoelectron spectra of different trivalent ions doped and undoped PWO are reported. The scintillation characteristics of the La-doped、Y-doped、Bi-doped、Sb-doped PWO crystals are discussed by comparing with the result of undoped PWO crystal. All the trivalent ions but Bi3+ doping gave a significant improvement in luminescence property of PWO obviously. The defects in PWO crystals caused by trivalent-ion dopants have been studied by means of positron annihilation lifetime and x-ray photoelectron spectra. The results can be stated as follows: La dopant can increase the concentrations of both lead vacancy (VPb) and the low-valent oxygen; Y and Bi dopant can decrease the concentrations of both VPb and low-valent oxygen; and Sb dopant can increase the concentration of VPb but decrease the concentration of low-valent oxygen. We consider that the La ions will replace the lattice Pb2+, the Y and Bi ions will occupy the lead vacancy; and the Sb ions have two valence states (+3 and +5), which will replace the lattice Pb2+ and W6+ ions, respectively.
Oxidation-induced stacking faults in nitrogen-doped czochralski silicon investigated by transmission electron microscope
2004, 53 (2): 550-554. doi: 10.7498/aps.53.550
The extended-defects generated during oxidation in both of nitrogen-doped Czochralski (NCZ) silicon and common Czochralski (CZ) silicon have been investigated by Transmission Electron Microscopy(TEM). It is found that the size of the oxidation-induced stacking faults (OSFs) decreases with the increase of oxidation time in NCZ silicon, and punched-out dislocations could also be observed. While in CZ silicon, there are many polyhedral oxygen precipitates generated, and the size of OSFs increases with increasing oxidation time.
2004, 53 (2): 555-560. doi: 10.7498/aps.53.555
Helium concentration profile, preservation dose and release rate from a nanocrystal titanium film implanted with helium at different energy and dose have been measured by proton Rutherford backscattering technique in a range from room temperature to 500℃. It is observed that the implanted helium may be stably preserved for a long time in the nanocrystal titanium film in the temperature environment from room temperature to below 100℃ when its concentration in up to 41%—52% of He-Ti atomic ratio, and also may be effectively preserved for a long time at room temperature if their atomic concentration ratio is up to 52%—74%. Possible mechanism of helium effectively preserved in the nanocrystal film with a large boundary volume ratio is preliminarily discussed from the energy viewpoint in this paper.
2004, 53 (2): 561-565. doi: 10.7498/aps.53.561
In this paper we suggest a radiation mobility shift model for the nonuniform channel metal-oxide-semiconductor(MOS). The distribution of two-dimensional(2D)-electric field and 2D-interaction potential, which is caused by the interaction between the ionized impurity in the depletion layer and radiation-induced positive spatial charge, is analyzed by using image charge method. The mobility expression of n-type and p-type nonuniform channel MOS is proposed. Using 2D simulator MEDICI, we simulate the mobility shift with the radiation-induced positive spatial charge. The nonuniform channel MOS's mobility shift numerical results agree well with the analytical results. Uniform channel MOS's mobility shift value agrees with that of the experiment.
2004, 53 (2): 566-570. doi: 10.7498/aps.53.566
Swift heavy ions delivered by Heavy Ion Research Facility at Lanzhou(HIRFL) were used to bombard the 32k SRAM IDT71256 at angles from 0°—85°. The multiple bit upset(MBU) ratio can reach as high as 70% when the device was tested with 15.14MeV/u 136Xe ions or at large angles with 36Ar ions. The angular effect of cross section is mainly due to occurrence of MBU especially at large angles. The MBU ratio is determined by the energy deposited in the whole sensitive layer and that of more than two bit upset is increased with incident angle.
2004, 53 (2): 571-576. doi: 10.7498/aps.53.571
Hard brittle particles can have an important influence on cleavage fracture in steels, and can act as cleavage initiators. Considering the strain elastic energy and the dislocation pile-up elastic energy to be released, and surface energy to be produced, during the hard brittle particle cracking, the mechanism of crack formation at hard brittle particles in steels was studied by a thermal dynamic model. It has been demonstrated theoretically that both normal stress and dislocation pile-up at the hard brittle particles are necessary for its cracking. Furthermore, a criterion for hard particle cracking has been derived, by which the critical cracking stress for the hard brittle particle was predicted not only to depend on its size and surface energy, but also to have correlations with the grain size. Their correlations are the same as the relationship between the fracture stress determined experimentally and the grain size in the case of finer grain constituents. It can be indicated that in such a situation the hard brittle particle cracking is responsible for the ultimate cleavage fracture of the material. In the case of coarser grain constituents, the critical cracking stress for the hard brittle particle is smaller than the fracture stress determined experimentally. This indicated that propagating a particle-size crack into the surrounding ferrite matrix is the critical event for the ultimate failure of the material.
2004, 53 (2): 577-581. doi: 10.7498/aps.53.577
The t-J model is one of the most important models that is often used to study the theory of the effect of strong electron correlations and high-Tc superconductivity. In this article, the method of renormalization group is used to investigate the t-J model and the elementary excitation energy spectrum of the t-J model is obtained by using the flow equations. Using the symmetry of functions, we can solve the specific expression of the energy spectrum. The result is compared with the result of Green's function method.
Aluminum-induced rapid crystallization of a-Si films at low temperatures in an electric field and microstructure analyses of the crystallized films
2004, 53 (2): 582-586. doi: 10.7498/aps.53.582
Aluminum-induced crystallization of amorphouse silicon (a-Si) is a suitable method for preparation of polycrystalline silicon (poly-Si) films. Biasing an electric field, which is perpendicular to the surface of the a-Si films, will accelerate the mutual diffusion of Al atoms and Si atoms in the interface during the aluminum-induced crystallization process and enhance the crystallization of the a-Si films obviously. The experimental results show that under the action of the electric field, more than 60% of a-Si transfer into poly-Si when the a-Si film was annealed at Ta＝400℃ and annealing time ta=60min; the a-Si films have obviously crystallized at Ta＝450℃ and ta=30min; at Ta＝500℃ and ta=15min, the XRD intensity of crystalline silicon (c-Si) components in the films is thrice to fourfold as strong as that in the films without the effect of an electric field.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2004, 53 (2): 587-591. doi: 10.7498/aps.53.587
Photo-induced resistivity change p has been studied in perovskite manganite La2/3Ca1/3MnO3 thin films with a continous wave laser and modulated laser pulses in this paper. Experimental results show that in the sample films, the maximum of photo-induced resistivity change（ΔR/R）max can reach 43.5%,which is a very exciting figure in this research field. Modulated laser pulse induced signal intensity has a highly nonlinear relation with the applied current and temperature. The maximum of photo-induced resistivity increase is a second power function of the applied current, while the temperature at which the maximum appears is proportional to the bias current. There exist an optimal bias current and a temperature for optical response in this film. These results are attributed to the optical excited eg↓ carriers and polarons.
2004, 53 (2): 592-595. doi: 10.7498/aps.53.592
By using the tight-binding molecular dynamics (TBMD) method, the structures and energies of the medium-sized silicon clusters (Si11—Si32) have been simulated, and the radial distribution function and bond-angle distribution for different size of clusters have been described in this paper. The structural transform from prolate to near-spherical configurations has been observed at the cluster size n=27 in silicon clusters.
2004, 53 (2): 596-600. doi: 10.7498/aps.53.596
The subbands occupation and subband transport properties in modulation-doped Al0.22Ga0.78N/GaN heterostructures are studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The occupation of two subbands is observed from the Shubnikov-de Haas oscillations. It is found that the total density of the two-dimensional electron gas (2DEG) as a function of the electron sheet density in the second subband is linear. The threshold of the 2DEG density that the second subband begins to be occupied is 7.3×1012cm-2. The transport mobility of the 2DEG in the two subbands is obtained by using the mobility spectrum technique. It is found that the transport mobility in the first subband decreases significantly when the relaxation of the Al0.22Ga0.78N barrier occurs. The electron mobility in the second subband is much larger than that in the first one. The results indicate that the interface roughness scattering and the alloy disorder are the main mechanisms in determining the 2DEG mobility in AlxGa1-x N/GaN heterostructures.
2004, 53 (2): 601-605. doi: 10.7498/aps.53.601
Measurements of the thermopower were carried out, from room temperature down to 10K, on the colossal magnetoresistance (CMR) thin films of the Pr2/3Sr1/3MnO3(PSMO) sample, which showed a dramatic reduction in the 1/f noise spectrum reported previously. At low temperatures, the thermopower is negative and shows metallic diffusion behavior of linear temperature dependence. As the temperature goes up near 150K, the thermopower reduces dramatically to show the behavior of 1/T temperature dependence,which is consistent with the prediction of the small polaron model for the high temperature phase of CMR materials. Compared with the temperature dependence of the resistance and the property of the 1/f noise near the phase transition peak, the conclusion can be reached that the percolation-typed phase separation exists in the phase transition temperature region.
2004, 53 (2): 606-613. doi: 10.7498/aps.53.606
Based on the theory of propagating electromagnetic plane waves in homogenous anisotropic media and 4×4 matrix method, the Kerr spectra for the MnBi multilayered films as a function of wavelength, incident angle and layer number are simulated. It is found that the calculated Kerr spectra as a function of wavelength are in good agreement with the experimental ones for MnBi,Mn0.53Bi0.47，Mn0.52Bi0.44Sb0.04. In addition, the Kerr spectra as a function of incident angle and layer number for the MnBi multilayered films are simulated. The calculated results indicate that the magnetic layer number and incident angle greatly affect the Kerr spectra. A maximum Kerr rotation exists at some thickness of the magnetic film as the wavelength of the incident light is normal. Also, a maximum rotation is found in the simulated Kerr rotation as a function of incident angle at a fixed thickness of magnetic layer. These simulated results is important for the design of the materials.
2004, 53 (2): 614-619. doi: 10.7498/aps.53.614
The exchange-coupled films (GdFeCo/DyFeCo) were prepared by sputtering method. The magnetization transitions caused by temperature changes had heen investigated for the films.The results indicate that the magnetization direction of the readout layer changes from in-plane to perpendicular when temperature increases.The transition occurs mainly as a result of the changes in the saturation magnetization. When the temperature increase to near the compensation temperature, the saturation magnetization and the demagnetizing energy of the GdFeCo layer decrease, With the exchange-coupled interaction,the magnetization direction of the readout layer changes.The films can be used for center aperture detection type magnetically induced super resolution.
2004, 53 (2): 620-625. doi: 10.7498/aps.53.620
We report out experimental results on Z-scan characteristics of co-existence of Kerr effects and transient thermo-optical effects in Kerr media in the nanosecond regime.The transition of peak-valley pattern under a certain condition was observed.There is a basic agreement between experimental data and numerical modeling.Meanwhile, a new single peak pattern or platform pattern of Z-scan curves was observed while the transient thermally induced optical nonlinearity counterbalances with Kerr effects.The research is significant to analyze correctly Z-scan measurements using a nanosecond pulse laser.
The properties of GaN∶Mg films grown by MOCVD on SiC substrate were studied using SEM, Raman scattering and photoluminescence spectra. The results indicate that some Mg atoms substitute Ga to become acceptors, while most of them exist as Mg interstitials(Mgi) and aggregate at defects and dislocations to reduce the tensile stress, hence a great deal of cracks were introduced during decreasing temperature process for inhomogeneous strain distribution. On the other hand, the incorporation of Mg aggravates disorder and debases the film quality. Finally, the room temperature photoluminescence measurements show the blue band attributed to DAP-type transitions from a deep donor(MgGaVN) to a shallow acceptor(MgGa).
2004, 53 (2): 631-635. doi: 10.7498/aps.53.631
Absorption spectra, emission spectra, excitation spectra, and upconversion luminescence of Er3+, Tm3+ co-doped NaY(WO4)2 crystal were measured at room temperature. Intensity parameters are calculated from absorption spectra in terms of Judd-Offelt theory. Transition processes of the energy levels of Er3+ and Tm3+ were analyzed in details and the cross relaxations: 1G4(Tm3+)＋4I15/2(Er3+)→3F4(Tm3+) +4F9/2(Er3+) ,1G4(Tm3+)＋4I15/2(Er3+)→3H5(Tm3+)＋4I9/2(Er3+), 3F4(Tm3+)＋4I9/2(Er3+)→3H6(Tm3+)＋4S3/2 or 2H11/2(Er3+) and 4F9/2(Er3+)＋3H6(Tm3+)→4I15/2(Er3+)+3F3(Tm3+) were put forward. Sufficient proofs have been found to illustrate the use of Er3+ as a sensitizer which is effective for the Tm3+-doped crystal.
Influences of processing parameters on the properties of ZnO thin films prepared by sol-gel spin-coating
2004, 53 (2): 636-639. doi: 10.7498/aps.53.636
Zinc oxide films were prepared on Si(111) substrates by sol-gel spin-coating technique.Structure,photoluminescence,and surface morphology of ZnO thin films processed at various temperatures and times were investigated.Results showed that ZnO thin films showed a hexagonal wurtzite structure,and the extent of c-axis orientation was dependent on the processing temperature.All the thin films emitted strong band to band UV emission without defects related visible emissions at room temperature when the processing temperature was below 550℃.When the processing temperature exceeded 550℃,a strong emission band appeared in the visible region.Results also showed that the photoluminescence spectrum was dependent not only on the processing temperature but also on the processing time.Long time(3 hours) processing resulted in the aggregation of ZnO grains in the film and a lower band to band emission in the photoluminescence spectrum.
2004, 53 (2): 640-645. doi: 10.7498/aps.53.640
The optical polarization dephasing times in bulk GaAs and GaAs/Al0.3Ga0.7As quantum wells at room temperature are measured using time-resolved degenerate-four-wave mixing (DFWM). Under the conditions of excitation pulse central wavelength of 785nm and carrier density of 1011cm-2, the dephasing times of 28 and 46 fs for bulk GaAs and multiple quantum wells, respectively, are measured. Because the carrier-carrier scattering rate in quantum wells is reduced due to the confinement of the carrier behavior，the dephasing time of the quantum wells is longer than that of bulk. The dependence of the DFWM signal on the intensity and the polarization of the incident pulses is evaluated by a theoretical model of third-order nonlinear density matrix.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2004, 53 (2): 646-650. doi: 10.7498/aps.53.646
Highly oriented ZnO whiskers were prepared on glass substrates by metal-organic chemical vapor deposition (MOCVD) at atmospheric pressure. X-ray diffraction result reveals that ZnO whiskers grow along ［0001］ direction and the crystal structure of ZnO is of wurtzite type. Scanning electron microscopic observations show that the length and shape of the whiskers are almost uniform. The diameters range from 100 to 800nm ,and the curvature radius of the whisker tip is about 50nm or even less. The chemical reaction process during the preparation of whiskers is discussed and a simple growth model of ZnO whisker deposited by MOCVD is proposed.
2004, 53 (2): 651-655. doi: 10.7498/aps.53.651
Defects constructing a netlike cell structure in the 3-inch semi-insulating gallium arsenide (SI-GaAs) single crystal were studied by methods of chemical etching, x-ray anomalous transmission topography (XRT) and transmission electron microscope (TEM). The nature and the formation mechanism of these structures were analyzed. It is assumed that the cell structures are made by the clusters of small angle grain boundary caused by the movement and interaction of high density of dislocations. and the cell wall is the typical small angle grain boundary. The phase difference among the small angle grain boundaries increases with the density of dislocations.
2004, 53 (2): 656-660. doi: 10.7498/aps.53.656
Non-polished aluminum sheets were anodized and the coexistence of self-assembled stripes and porous arrays on the Al surface was observed. The nanostructures were investigated in details using an atomic force microscope. And the formation mechanism of the stripes was discussed and simulated using Brusselator model in this work. We demonstrated that the self-assembled patterns on the Al surface were governed by the competition of formation and dissolution of alumina film during the reaction process. Moreover, this type of ordered structure could only form in certain conditions.