Vol. 45, No. 10 (1996)
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
1996, 45 (10): 1601-1608. doi: 10.7498/aps.45.1601
Starting from the quantization formalism of the phase-space path integral for a system with a singular Lagrangian, the generalized canonical Ward identities and conserved charges at quantum level are deduced under the global transformation in extended phase space. In general, the quantal conserved charges are different from classical ones. We give a preliminary application to Yang-Mills theory,the new quantal conserved charges are found.
ATOMIC AND MOLECULAR PHYSICS
RELATIVISTIC MULTICONFIGURATION CALCULATION OF FINE-STRUCTURE ENERGY LEVELS AND TRANSITIONS FOR Cu-LIKE Au50+
1996, 45 (10): 1609-1614. doi: 10.7498/aps.45.1609
The fine-structure energy levels and transition parameters of Cu-like Au50+ have been calculated by using the relativistic multi-configuration method(GRASP 2,1992) with the corrections of finite nuclear size, Breit and QED. The results obtained are in good agreement with the experimental data available and better than those of the previous calculations. It can be concluded that the QED correction should be taken into account further, which greatly improves the accuracy of the calculated 4s—4p transition wavelengths.
In this paper, we report the recent results about photovoltaic effects in a metal (Al or Au)/porous silicon(MPS)structure. We have given the spectral response curves of the Schottky diode structures of the first time, and investigated the dependences of the open circuit voltage on the incident light intensity and the measurement temperature. The results obtained show that the Schottky junction between the metal and the porous silicon layer should be the principal source of the photovoltaic actions, while the heterojunction between the porous silicon layer and the silicon substrate could impede the transport of the forward current in this structures. It is also found that the open circuit voltage increases linearly with decreasing of temperature in the range of 300—120K and the temperature coefficient is ～2.0mV/K and ～2.8mV/K for Au/PS and Al/PS diodes, respectively.
1996, 45 (10): 1622-1628. doi: 10.7498/aps.45.1622
The dependence of Cs saturated absorption spectra on the intensity of pumping light, especially that of the spectrum of ６２Ｓ１／２Ｆ＝４→６２Ｐ３／２Ｆ′＝５, was measured and calculated. When the pumping light and probing light were linearly polarized, the relative magnitudes of the resonance signals were calculated by solving a set of rate equations with Runge-Kutta algorithm, taking into consideration the optical pumping process and the saturation in the Zee-man sublevels of the hyperfine structure. The theoretical calculations were in good agreement with the experimental results.
1996, 45 (10): 1629-1635. doi: 10.7498/aps.45.1629
This work deals with the multiphoton dissociation of diatomic molecule in intense IR laser field, the interaction between field and molecules is approximated to that between field and the dipoles. The Ｓｃｈｒ?ｄｉｎｇｅｒ equation is solved by using Close-Coupling method and Floquet theory. Numerical results for molecule HF are given.
1996, 45 (10): 1636-1640. doi: 10.7498/aps.45.1636
The emission cross sections and excitation cross sections have been measured in collisions between N4+ ion and Na atoms. The experimental results show that the excitation cross sections of NaI(3p-3s) are vety large, about １０-15ｃｍ2 . The data of cross sections have been given in this paper and reasons for the large excitation cross sections of NaI(3p-3s) have been discussed qualitatively.
1996, 45 (10): 1641-1646. doi: 10.7498/aps.45.1641
The collision strengths of excitation by electron impact from nl to n′l′ with n(n′)≤7 of Li-like ions are computed systematically. The results agree with available data within 10%. The collision strengths are scaled and fitted with a least-squre spline method. As a result, the collision strengths and thermally averaged rate coefficients in the entire range can be determined by ten parameters for one transition process.
CLASSICAL AREA OF PHENOMENOLOGY
1996, 45 (10): 1647-1654. doi: 10.7498/aps.45.1647
Based on the general theory of the optical transformation, a new method for designing diffractive phase elements generating multi-focal annuli is presented. The number and the position of focal annuli, as well as the width of focal annuli may be predetermined arbitrarily according to the particular demands. Several simulation designs are carried out for the Gaus-sian-profile laser illumination. We also investigate the influence of phase quantization on the results of designs. The simulation calculations show that the new method can be successfully applied to the designs of the desired diffractive phase elements for generating multi-focal annuli.
1996, 45 (10): 1655-1659. doi: 10.7498/aps.45.1655
The photorefractive holographic grating in a Mn doped K1-yNayBa2-xSrxNb5O15 (KNSBN) is written with two 0.27mW He-Ne laser beams (632.6nm) and is read with one quasicontinuous dye laser beam (621.8nm, 1.6mW or less). It is found that the Bragg diffracton suddenly reaches its maximum at the beginning and then decays to its minimum with a time constant of about 0.6s. The ratio of the maximum to the minimum can be higher than 7.5. A theory including pyroelectric effect has been developed and it fits the experiment well.
1996, 45 (10): 1660-1670. doi: 10.7498/aps.45.1660
A theory of multimode oscillation in an optical unidirectional ring resonator with photorefractive gain was given in the weak-field limit. In nondegenerate state, the system is stable and can be described by Lotka-Voterra equation. While the system will becomes unstable in certain circumstance owing to the mode-mode interaction in the degenerate or quasi-degenerate condition, such as the periodic alternation behavior.
1996, 45 (10): 1671-1676. doi: 10.7498/aps.45.1671
The phenomena of dark spatial optical soliton and soliton-induced flexible optical wave-guide have been observed, which are induced by thermal self-defocusing effect of Ar+ laser beam in C60-toluene solution. The numerical simulations of the formation process of dark spatial soliton using the nonlinear Schr?dinger equation are consistent with the experimental results.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1996, 45 (10): 1677-1687. doi: 10.7498/aps.45.1677
The self-modified quasi-stationary model for radiation ablation has been established in this paper based on physical picture of numerical simulations. The objective of the model is to predict quantitatively the scaling laws of various ablation parameters driven by soft-X-ray, such as the dependence of ablation depth, pressure on radiation temperature, energy, pulse width, without resorting to complex computer simulations. The computational results are given fot some interstng materials in ICF. Scaling laws obtained in this paper are simple and effective in target design and analysis of experimental results.
STUDY OF SOFT X-RAY CONVERSION EFFICIENCY FROM FREQUENCY-TRIPLED 0.35μｍ LASER-IRRADIATED DIFFERENT MATERIAL PLANAR TARGETS
1996, 45 (10): 1688-1693. doi: 10.7498/aps.45.1688
Soft X-ray conversion efficiencies from 0.35μｍ laser-irradiated Au disk and C, Al, Cu foils at different laser intensity on the "Xingguang Ⅱ" high-intensity laser facility (energy ５—９０Ｊ，focal spot～２００μｍ，FWHM４００—８００ｐｓ）were obtained. A simple model was given to explain soft X-ray conversion efficiency from ０.３５μｍ laser-Al plasma interaction. In this model,bccause of heat conduction from the laser-heated spot, the conversion was very small at some low irradiancc limit, while at some high irradiance limit it was bounded by the energy lost in plasma blowoff. Consequently, at laser intensity(2±0.5)×１０１4Ｗ／ｃｍ2,the X-ray conversion efficiency reaches a maximum.
1996, 45 (10): 1694-1703. doi: 10.7498/aps.45.1694
The electron density fluctuations of CT-6B Tokamak plasma have been studied in detail through the observation of Hα emission intensity by multichannel optical diagnostics. Their various behavior, such as power spectrum, fluctuation level and correlation,have been measured. The experimental results show that some characteristics of density fluctuations are founded in CT-6B Tokamak plasma: the density fluctuation level is about 10%-90% in the radial range r=4-10cm; the point in the range draws, nearer to the edge of plasma the level lecomes higher. A broadband power spectrum is observed at observed points along the plasma radius. There exists a local correlation structure with short correlation time, about 0.2-0.5ms, and short correlation distance , about 0.5-1cm,in the edge of plasma.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1996, 45 (10): 1704-1708. doi: 10.7498/aps.45.1704
The diffracted and transmitted rocking curves for GaAs(600) in the symmetric Bragg case have been measured under the condition of extremely anomalous scattering near the Ga K-absorption edge, and then compared with the corresponding results calculated in the dynamic theory of X-ray diffraction. We have thereof pointed out that the transmitted rocking curves near the atomic absorption edge in Bragg case are useful in the study of anomalous scattering.
1996, 45 (10): 1709-1716. doi: 10.7498/aps.45.1709
A AlAs/GaAs/AlAs/AlGaAs double-barrier superlattice grown on GaAs substrate by MBE has been studied by combining double-crystal X-ray diffraction and synchrotron radiation. This combination provides a comprehensive structural analysis. During simulated by X-ray dynamical diffraction theory, we find the intensity of satellite peaks which situated near-by the modulated wave point of one layer are very sensitive to the variation of the layer's structural parameters. Accoding to these, the accurate layer thickness can be get with an error less than 0.1nm. The modulated phenomenon is investigated by X-ray kinematical diffraction theory.
1996, 45 (10): 1717-1723. doi: 10.7498/aps.45.1717
Electron-phonon interactions and phonon excitations are studied on the models both for the halogen-bridged moxed-valence transition-metal linear complexes(MX) and the molecular crystals (MC). The renormalized phonon dispersions are obtained under the adiabatic approximation. We find:(1) the electron-phonon interactions are different for the two models, and then the renormalization correction on the acoustic phonons is negligible for the MX model whereas the correction is obvious for the MC model;(2) no gap exists between the two branchs of phonons for the two models, which is different with that of the Su-Schrieffer-Heeger model for polymers.
1996, 45 (10): 1724-1728. doi: 10.7498/aps.45.1724
The amorphous Nb/Si multilayers were prepared for the interdiffusion study. The temperature dependent effective interdiffusion at low temperature in amorphous Nb/Si multilayer was obtained using in-situ XRD technique. The smaller pre-exponential factor for diffusion coefficient in amorphous Nb/Si multilayer is explained by the trap-retarded diffusion mechanism. In this model, the atomic vibration frequency v is substituted by the average characteristic atomic vibration frequency v because of the presence of defect traps.
1996, 45 (10): 1729-1736. doi: 10.7498/aps.45.1729
ＰｂＴｉＯ３ thin films were deposited on (001) redoping n-Si, (001) SrＴｉＯ３ substrates by low-pressure MOCVD technique, XRD θ－２θ scan shows that the film on Si substrate has a polycrystalline structure, while the other two films have preferential orientations and their epitaxial nature was confirmed by the X-ray φ scan, rocking curves of the two epitaxial thin films were taken at BSRF using the synchrotron radiation. The film on LaAlＯ３ substrate has an a,c domain coexisting structure, and the film on ＳｒＴｉＯ３ substrate only has a c-orientation. All the films exhibit a c-axis shortening compare with the bulk material, and the reason can be attributed to the size effect and surface influence. The ferroelectric properties of the polycrystalline thin films were investigated using the redoping Si substrate as bottom electrode directly, and the ＰｂＴｉＯ３ thin film shows a perfect hysteresis loop.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1996, 45 (10): 1737-1743. doi: 10.7498/aps.45.1737
Electronic structure for BKB has been calculated by using LMTO-ASA-Supercell method based on the X-ray absorption fine structure (XAFS) spectroscopy measurements. Measurements show that Bi posseses two valence states Ｂｉ３＋ and Ｂｉ5＋ and their Bi—Ｏ bond lengths are diffferent, the difference decreases with the increase of K concentration. Calculations are performed on five samples namely Ｂａ4Ｂｉ4Ｏ12（４０４），（Ｂａ３Ｋ）Ｂｉ4Ｏ12（３１４），（ＢａＫ）Ｂｉ2Ｏ6（１１２），（ＢａＫ３）Ｂｉ4Ｏ12（１３４），Ｋ2Ｂｉ2Ｏ6（０２２）.Results from the calculations show that （404）and (314)are semiconductors with gaps of 1.6eV and 1.5eV, respectively. Other samples are metals. Total energy analysis shows that (314) is not stable, so that the extreme value of x is 0.5. The BKB electronic structures at x=0.1 to 0.5 are calculated by combining the probability with sample's Bernoull's distribution. Superconducting transition temperature Tc of BKB is suddenly changed when x approximates to 0.25. The experimental data are close to the prediction values of percolation theory.
1996, 45 (10): 1744-1748. doi: 10.7498/aps.45.1744
[Fe/Cr],[Fe/Cr/Si] and [Fe/Si] multilayered systems were prepared by the vacuum evaporating method. The effects of the altered space thicknesses of the nonmagnetic Cr,Si and Cr+Si layers on the exchange coupling and the magneto resistance of those multilayers were studied. The Fe layers were fixed on 2.0nm. The oscillation of the interlayer coupling and the giant magnetoresistance (GMR) and its oscillation with the change of the Cr layer thickness were observed. The GMR was 14.6% at 4.2K. Three was no oscillatory effect of the exchange coupling and GMR in the [Fe/Si] and [Fe/Cr/Si] multilayers was found. According to the increases of the resistivity of the samples doped with Si layers, we believe the conducting electrons in the nonmagnetic layers should decrease largely. This would be the cause to reduce the polarization effect of those electrons in the space layers. Then the oscillatory exchange coupling disappeared and the magnetoresistance was much reduced.
1996, 45 (10): 1749-1755. doi: 10.7498/aps.45.1749
Investigations on magnetocaloric effect and magnetic entropy,Curie temperature and specific heat of nanometer binary gadolinium alloys such as Gd-Y,Gd-Tb and Gd-Zn have been carried out under the conditions of a low magnetic-field intensity(1T) and a temperature range within 233～313K. Both Curie temperature and specific heat of the prepared nanometer alloys,compared with the bulk materials,show obvious decrease and increase respectively. The nanometer alloy Gd-Y demonstrates an enhanced magnetocaloric effect and magnetic entropy over the same bulk material, which is of importance on researching and developing new materials for magnetic refrigeration. Adiscussion concerning the influence of nanometer structure on magnetic and heat properties mentioned above is given in detail.
1996, 45 (10): 1756-1761. doi: 10.7498/aps.45.1756
Raman scattering of Ge nanocrystallites from 4 to 16nm is size, embedded in ＳｉＯ２ thin films has been studied. The Ge-ＳｉＯ２ samples were prepared by ion-beam sputtering and a post-annealing technique. A red shift and broadening of the Raman peak observed with decreasing the size of Ge particles are in good agreement with the calculated results based on the phonon confinement theory. Effects of the surface and interface of the Ge-nanocrystallites on Raman spectra have also been investigated.
INTERSUBBAND ABSORPTION COEFFICIENTS IN A QUANTUM WELL Ge0.3Si0.7/Si/Ge0.3Si0.7 WITH BARRIER-δ-DOPING
1996, 45 (10): 1762-1770. doi: 10.7498/aps.45.1762
The electronic structures and intersubband absorption coefficients of Ge0.3Si0.7/Si/Ge0.3Si0.7 quantum wells with barrier-δ-doping grown on Ge0.3Si0.7(001) substrates are consistently calculated in the envelopefunction approach. The dependences of the absorptivities on the well widths, δ-doping position and δ-doping concentration are discussed . At last, the frequency shift caused by the depolarization effects of highly dense two-dimensional electrons are studied.
1996, 45 (10): 1771-1776. doi: 10.7498/aps.45.1771
The properties of boron-doped diamond films prepared by hot filament CVD were studied with Raman spectra and X-ray microanalysis. It was found that the content of the graphitic type （Ｓｐ2)bonding in the CVD diamond was reduced at low boron concentrations, and the widening and shift of the characteristic diamond Ｓｐ3 Raman peak appeared in the diamond with increasing boron concentrations. This can be interpreted in terms of the lattice strain and Fano interaction caused by boron doping.