Vol. 48, No. 7 (1999)
1999-04-05
GENERAL
1999, 48 (7): 1185-1191.
doi: 10.7498/aps.48.1185
Abstract +
We present a general method to solve the stationary nonlinear Schr?dinger equation (NLSE) with an external potential. We apply it to the stationary states of NLSE for neutral atoms in a harmonic trap. We discuss the problems of convergence and normalization of NLSE wave function. The accuracy of calculation is analyzed.
1999, 48 (7): 1192-1197.
doi: 10.7498/aps.48.1192
Abstract +
A W-shaped magneto-optical potential trap with axial symmetry is proposed. The Bose-Einstein condensate confined in the trap is ring-shaped. The ground state wave functions for two extreme cases, the noninteraction and strong repulsive limits, are calculated. The critical temperature is analyzed.
1999, 48 (7): 1198-1203.
doi: 10.7498/aps.48.1198
Abstract +
A theoretical result of impulse synchronization of R?ssler systems is given. Based on the theory of impulse differential equation, a linear impulsive feedback synchronization rule is proposed according to synchronization errors. The condition of synchronization asymptotic stability of the rule is described and an example is given to demonstrate the effectiveness and robustness to noise in the use of the method.
ATOMIC AND MOLECULAR PHYSICS
1999, 48 (7): 1204-1209.
doi: 10.7498/aps.48.1204
Abstract +
About 50 spectral lines due to the (2+1) resonance-enhanced multiphoton ionization (REMPI) of atomic sulfur, generated in the sequential multiphoton dissociation of SO2 at probing wavelengths, in the 243—263 nm region has been observed. Besides most of the lines which are due to the two-photon transition from the ground states 3P2,1,0 to the Rydberg states 3P, 3D, 3F until n=10 of S atom, several new lines including the spin forbbiden transition 1P0, 5S0←3P and the two-photon transitions from the excited state 1D2 to the Rydberg states np1,3D, 1,3F are observed. Intensities of some lines have been calculated and compared with the experimental results.
1999, 48 (7): 1210-1214.
doi: 10.7498/aps.48.1210
Abstract +
In the text we have calculated the potential function, electron momentum distrbutions and charge stripping cross sections for 36Krq+ collision with H and He using binary encounter approximation and Thomas-Fermi approximation methods.
1999, 48 (7): 1215-1222.
doi: 10.7498/aps.48.1215
Abstract +
This paper reports a molecular dynamics simulation for atomic structure of copper nanocrystals, in which the grain size and lattice distortion were computed by X-ray differaction simulation, and the distribution of energy and elastic modulus was calculated. The results show that the lattice distortion was stored not only at grain boundaries but also in the grain. The increase of atomic radius leads to the reduction of the elastic modulus of the nanocrystals.
CLASSICAL AREA OF PHENOMENOLOGY
1999, 48 (7): 1223-1229.
doi: 10.7498/aps.48.1223
Abstract +
In this paper, the Huygens-Fresnel principle is restudied by means of wavelet analysis firstly, this builds the basis of the theory for wavelet optics. Then the theory of wavelet analysis is used to analyze the filtering in spatial domain and spatial frequency domain. For example, it gives the space variable processing for the filtering with wavelet in spatial domain, the match filtering for the filtering with wavelet in spatial fequency domain and a single slit and a round aperture for the wave-front filtering. The feasibility for treating the problems in optical field with wavelet transform is discussed, and the theoretical frame of wavelet optics is built.
1999, 48 (7): 1230-1235.
doi: 10.7498/aps.48.1230
Abstract +
The fourth-order quantum interference of squeezed fields generated by two independent optical parametric oscillators(OPOs) is discussed based on the semi-classical theory. It is shown that at the oscillation threshold of OPOs the squeezing of two output fields is the highest but the fringe visibility of fourth-order interference is the lowest(33.3%). When the pump power is away from the thres-old, the squeezing decreases while the correlation between them increases.
1999, 48 (7): 1236-1247.
doi: 10.7498/aps.48.1236
Abstract +
In this paper, an optical array resonator with phase-shifting end mirror has been combined with the RF-excited diffusively cooled slab waveguide CO2 lasers to obtain a desirable output laser beam with single-peaked far-field intensity distribution, which is highly spatially suppressed with the merits of high brightness and good characteristics of propagation. In the experiments, a maximum output power of 46 W and highest conversion efficiency of 11.3% have been obtained from a 200-mm-gain-length device. The laser beam intensity distribution acquired has similar characteristics to the ouptut beam from laser arrays due to the periodical structure of the phase-shifting total reflector, and has an excellent stability due to the mode-selection capability of this type of resonator. In this paper, theoretical analysis is also given, based on which corresponding theoretical model is established, the practical feasibility is shown, and the laser beam output with characteristics of in-phase array mode is predicted. The systematical experimental investigation indicates the prominent influence of the parameters of the phase-shifting array end mirror on the property of the output beam. Furthermore, the manufacturing errors of the phase-shifted array resonator are analyzed and the analysis provides a theoretical guide to the design of this type of lasers.
1999, 48 (7): 1248-1253.
doi: 10.7498/aps.48.1248
Abstract +
Using equations governing the variation of the beam size and the curvature of wave front in the logrithmically saturable nonlinear media, the Gaussian-type breath mode of spatial soliton has been described in detail. With the aid of a potential method, the positive and negative signs can be assigned to the first order derivative of the beam size with respect to the propagation distance. Thus, important parameters of the breath mode, such as the beam size, curvatwre radius of the wave front, the period, etc., have been calculated.
1999, 48 (7): 1254-1260.
doi: 10.7498/aps.48.1254
Abstract +
The vector theory to describe off-axial Gaussian wave is proposed, and an accurate far-field propagation formula is derived. The light wave characteristics and propagation properties are discussed in detail, and the comparison between the vector theory and the scalar theory is also made.
1999, 48 (7): 1261-1268.
doi: 10.7498/aps.48.1261
Abstract +
The formation energies of point defects in CaF2, SrF2 and BaF2 were calculated in terms of the shell model parameters and potential parameters of the interaction between the ions in these alkaline earth fluoridds, which had been determined by empirical parameterization. Moreover, the calculated phonon dispersion relations for SrF2 and BaF2 were compared with the data of inelastic neutron scattering a retest for the quality of these parameters.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (7): 1269-1274.
doi: 10.7498/aps.48.1269
Abstract +
C60 films were irradiatied ar room temperature by medium-energy(120—360 keV) radiation of different ions (H+, He+, N+, Ar+), and the radiation effects were investigated using Raman spectra. The results showed that the radiation of medium-energy ions could cause C60 films polymerized and amorphous. However, occurrence of the phenomena depends on dosage, which is related to the interaction between the radiation ion and C60 molecule. A possible explanation for the experimental results is given and the mechanism of the interaction between the radiation ion and C60 molecule is discussed.
1999, 48 (7): 1275-1281.
doi: 10.7498/aps.48.1275
Abstract +
The scattering trajectory and stopping power for H+ ions at glancing angles of incidence on a solid surface have been investigated using the dielectric response theory and specular reflection model. When an ion moves near the solid surface, it will be subjected to the repulsive force of the surface atoms and the dynamical force yielded by the surface induced potential. A local-field correction dielectric function and a local frquency-dependent dielectric function with a damping factor have been adopted respectively in low and high velocity approximations. The energy loss is obtained and has been compared with the experiment results.
1999, 48 (7): 1282-1291.
doi: 10.7498/aps.48.1282
Abstract +
A representative PbWo4 sample was annealed subsequently from 640 to 1040℃ in air and the optical absorption spectra were measured after each annealing step. It was found that the intrinsic color center absortion band peaking at 350 nm increased after annealing at lower temperature, then with increasing annealing temperature it decreased continuously until it was removed finally. Based on the analysis of intrinsic defects and corresponding charge compensation of PbWO4 crystals, the creation and transformation of the color center were discussed. This was caused by the diffusion of oxygen, entering into PWO crystals during the annealing process. It was supposed that a Pb3+→Pb4+ transformation probably occurred in the annealing process, it would lead to annihilation of Pb3+ centers. The UV radiation induced color center absorptions of PWO crystals annealed at different temperatures were measured and compared. It has been observed that the O- hole centers as the main product of the radiation damage of PWO crystals were produced predominantly from the transformation of the intrinsic Pb3+ hole centers. On the other hand, oxygen vacancies VO as electron trap centers trapped the electrons during irradiatiion, thus stabilizing O- hole centers. When those two factors have been removed by means of annealing at high temperature in air(oxygen abundant atmosphere), the radiation hardness of PWO crystals can be effectively improved. While, the iron impurity in crystals is very harmful for the radiation hardness of PWO crystals.
1999, 48 (7): 1292-1296.
doi: 10.7498/aps.48.1292
Abstract +
By electrolysis of the methanol and urea solutions CNx thin films have been synthesized on silicon substrates at atmospheric pressure and low tempreture (60℃). The FTIR and Raman measurements show that the films are amorphous carbon network with the staples of many C—N, C—C, C＝C and C＝N bonds and a small portion of C≡N bonds. The XPS measurements indicate that nitrogen atoms is chemically bonded to carbon atoms through hybridized SP2 and SP3 configurations. The structures of the amorphous CNx thin films deposited by this method are every similar to those by vapor depositions.
1999, 48 (7): 1297-1301.
doi: 10.7498/aps.48.1297
Abstract +
By means of the optical phase retardation method the YAG laser was used to observe the transient heating behavior in planar nematic liquid crystals. According to the experimental results, heating effect may induce molecular reorientation in liquid crystals. Azo-dye and photoisomerized-dye in planar nematic liquid crystals have little effect on heating behavior, but the liquid crystal doped with chiral molecules shows temporary memory effect.
1999, 48 (7): 1302-1308.
doi: 10.7498/aps.48.1302
Abstract +
The relationship between temperature of substrate and island morphology at the early phase of thin film growth has been investigated using Monte Carlo model. The relationship between island morphology and rest energy of vapor phase particles has also been obtained. Three kinds of dynamic processes, i.e.adsorption, diffusion and desorption are considered. The difference between our model and the previous one is that the impingement is considered to be independent of other processes, and the diffusion and desorption are correlated with each other. The results indicate that with increasing temperature, the island morphology evolves from dispersed growth, fractal growth to dense growth. At low temperatures, with increasing energy of vapor phase particles, the same evolution of island morphology is also observed.
1999, 48 (7): 1309-1314.
doi: 10.7498/aps.48.1309
Abstract +
The spatial distribution of the ECR plasma density has been measured by using an eccentric Langmuir probe. The result indicates that the plasma density is very uniform in the axis Z=50 cm and radial Φ=12 cm. Effect of the radial uniformity of plasma density on the uniformity of deposition rate and thin film thickness is analyzed. The repeatability to prepare silicon nitride thin film of a specified thickness is discussed. The relation of the deposition process with the deposition rate of silicon nitride thin film is investigated and the dependence of the practical application on process parameters has been obtained for the deposition thin film with ECR-PECVD technology.
1999, 48 (7): 1315-1319.
doi: 10.7498/aps.48.1315
Abstract +
In this paper, the growth GaN epilayer on the Si substrate by a novel vacuum reaction method rather than metal-organic chemical vapor deposition and moleculau beam epitaxy is reported. The effects of growth temperature and annealing process on the photoluminescence (PL) of GaN epilayer were investigated. Annealing could weaken the PL and the GaN epilayer grown at 1050℃ exhibited the strongest PL. It was demonstrated in secondary ion mass spectroscopy that both gallium and nitrogen were distributed uniformly within the epilayer, while gallium was segregated on the surface of epilayer. The high carrier concentration (1.7×1018/cm3) was associated with the impurities of silicon and oxygen and native defects existing in the epilayer. In-situ cleaning was proved to be efficient for the removal of oxygen on the silicon substrate.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1999, 48 (7): 1320-1326.
doi: 10.7498/aps.48.1320
Abstract +
Under the effective-mass approximation, considering the dielectric confinement effect, we use the variational method to calculated the binding energy and ground state energy of an exciton in spherical and cubic quantum dot (QD). The present result shown that the effects of QD shape on excitonic states in not negligible.
1999, 48 (7): 1327-1333.
doi: 10.7498/aps.48.1327
Abstract +
A tight-binding model for conducting polymer poly(phenylene vinylene) (PPV) has been suggested in the framework of one-dimensional chains. The calculations showed that this model is effective to describe the ground state, polaron and bipolaron excitations in PPV. The stability of polarons and bipolarons was discussed by considering the effect of the dimensions, e-ph and e-e interactions.
1999, 48 (7): 1334-1339.
doi: 10.7498/aps.48.1334
Abstract +
Based on the tight binding scattering theoretical method, the electronic strucutre of Sb adsorped on the surface of InP(110) is studied. Surface states and surface resonances are identified from the calculated local density of states along the four zone boundaries of the (110) surface Brillouin zone. Some results are in good agreement with the experiment and better than other theoretical results.
1999, 48 (7): 1340-1345.
doi: 10.7498/aps.48.1340
Abstract +
The variational approach is applied to the study of the ground state of quantum tunneling system interacting with two phonons by use of a correlated-squeezed transformation. We fine: 1) For the two phonons bath, the ground state energy of the phonons with correlation effect is lower than that without correlation effect; 2) The effect of correlation varies with the mode parameters: In the resonant regime of the phonons and two-state system, the correlation effect is more significant and will be strengthened together with the increase of coupling coefficient.
1999, 48 (7): 1346-1353.
doi: 10.7498/aps.48.1346
Abstract +
Using the tight-binding linear muffin-tin orbital(TB-LMTO) method, we investigated the magnetism and its pressure dependence of Fe-Al system in some bcc superstructures. The results indicate that the magnetic moment of Fe in the ferromagnetic state decreases with increasing concentration of Al in the system and the volume-compression. As the concentration of Al in the system is in excess of about 0.5 the magnetism of the system will transform from ferromagnetism to paramagnetism. On the other hand, there are no pressure-induced magnetic phase transitions in the bcc Fe-Al alloys; this is different from that in the fcc Fe(γ-Fe) and some fcc Fe-based alloys. The results are in good agree-ment with the experimental results.
1999, 48 (7): 1354-1360.
doi: 10.7498/aps.48.1354
Abstract +
The nanotubes were produced by dc arc-discharge method through helium and argon gas at a controlled pressure ranging from 10 kPa to 80 kPa. The crude nanotubes were oxidized at 770℃ until about 1% of the weight remained and the purified nanotubes were obtained. The electron spin resonance (ESR) of purified carbon nanotubes prepared under different inert gases with different pressures has been measured. The dependence of ESR line shape, linewidth, g value and spin density of the purified nanotubes on different inert gases and pressure is found and discussed.
1999, 48 (7): 1361-1371.
doi: 10.7498/aps.48.1361
Abstract +
The effects of energy transfer on luminescence decay curves are studied. Donor-acceptor energy transfer and donor-donor energy migration are considered simultaneously for solving the problems in previous models. Three models named I-H-B,D-H-B and V-F-B are established here. The RE ions luminescence decay curves of the elpasolite system under different conditions are calculated using the above models. The conclusion is that the V-F-B model is the best. Then the luminescence decay curves from the 4G5/2 state to 6H7/2 state of Sm3+ at 170K in Cs2NaSmxY1-xCl6 for six different concentrations are simulated successfully using V-F-B model.
1999, 48 (7): 1372-1380.
doi: 10.7498/aps.48.1372
Abstract +
The intensity distribution of a yellow luminescence band was observed by cathodoluminescence (CL) on GaN epilayers with different surface morphologies grown by metallorganic vapor phase epitaxy, which showed that the hexagonal hillock surface morphology had an effect on CL image of the yellow luminescence band. The polished epilayers were further investigated by CL image, atomic number contrast, and wavelength dispersive X-ray spectrometry, and were observed that the intensity of the yellow luminescence band was relatively strong around the defects associated microscope exhibited the structures of the defects different from that of GaN matrix, misfit edge dislocations and cracks. The results suggest that the defects may result from the precipitations in the V-shape grooves of imperfect coalescence during epitaxy.
1999, 48 (7): 1381-1388.
doi: 10.7498/aps.48.1381
Abstract +
The spectral characteristics of SrS:HoF3 thin films are investigated. The aim is to analyse the electroluminescent(EL) mechanism in the SrS:HoF3 thin film. Direct impact excitation mechanism is not the main excitation mechanism according to the relation between the EL spectra and the applide voltage. The ionization of the luminescent center could not happen because there is no trailing edge emission whe the thin film is driven by square voltage. Comparing the EL and photoluminescent (PL) spectra, we think the main excitation mechanism is that the hot electrons impact and excite the host and then their energy is transferred to the luminescent centers.
