Vol. 37, No. 10 (1988)
1988-05-20
CONTENT
1988, 37 (10): 1575-1584.
doi: 10.7498/aps.37.1575
Abstract +
The scanning and focusing of acoustic beam in solid by a Fresnel transducer array of planar structure is significant in many applications.In this paper, the acoustic field distributions of such beam were analysed by using the scalar theory and vector theory respectively. The theoretical analyses have been compared with experimental results.Finally, for the purpose of RF spectrum analysis, the transient time and the weighting of such focusing beam were discussed.
1988, 37 (10): 1585-1592.
doi: 10.7498/aps.37.1585
Abstract +
A new approach for the CPA treatment of band structure of semiconductor alloys based on the LMTO-ASA-VCA method is suggested, in which no adjustable parameter is needed. In. order to construct a set of orthonormal sp-like hybrid orbitals from calcutated eigenstates and apply for CPA calculation, it is found that the following procedure is suitable: in the process of LMTO calculation and its VCA treatment, d states of atoms should be included in the matrix elememts, and d-band hybridization effect may be regarded as negligible for the secu-ler equation calculation. This method is illustrated with GaAlAs alloys. The results indicate that the CPA's calculation values of bowing parameters of bands and band-edges are quite reasonable.
1988, 37 (10): 1593-1599.
doi: 10.7498/aps.37.1593
Abstract +
The chemisorption of Ce, Sm and Yb on Si(lll) surface are studied by calculation with local density formalism (LDF) and discrete variational method (DVM). Two different clusters are used to simulate the top site and 3-fold site. The calculation is carried out self-con-sistently and the binding energy of the cluster is obtained. Optimum geometry is determined by minimizing the total energy. Charge transfer between rare earth atom and the silicon substrate, the energy of chemisorption and the density of states are discussed and compared with experimental results available.
1988, 37 (10): 1600-1606.
doi: 10.7498/aps.37.1600
Abstract +
The properties of thermally nitrided SiO2 thin film and its interface have been studied. It is found that the chemical composition, refractive index, electron trap parameters, surface mobility, fixed charge and interfacial state densities are dependent obviously on the annealing condition in ammonia. The mechanism of nitridation, anti-oxidation, and the effect of nitridation on interfacial characteristics are discussed.
1988, 37 (10): 1607-1612.
doi: 10.7498/aps.37.1607
Abstract +
In this paper, we report the results of RHEED, AES studies of thin Ge film grown on the patterned Si substrates which are formed by room temperature Ge deposition followed with thermal annealing to cluster the deposited Ge into islands. Double crystal X-ray diffraction measurements show that the existence of Ge islands on Si substrate surfaces is effective for releasing the mismatch strain and improving the crystalline qualities of the epilayers then deposited on it.
1988, 37 (10): 1613-1618.
doi: 10.7498/aps.37.1613
Abstract +
Hall effect measurements were carried out on rf-sputtered Fe3O4 and γ-Fe2O3 thin films in magnetic field up to 1.4 T applied perpendicular to the film plane. Their ordinary and extraordinary coefficients are determined from the experimental data. The calculated values of the Hall mobilities for these two films are 2.35 and 1.56cm2/V·s respectively, which are larger than 1 cm2/V·s, suggesting the occurrence of large polaron scattering. The extraordinary Hall effects were compared by using Berger side-jumping model. The negative magnetic resistivity is also observed for these two films.
1988, 37 (10): 1619-1625.
doi: 10.7498/aps.37.1619
Abstract +
In this paper, we have studied the effect of Er3+ concentration ACEL characteristics of ZnS:ErF3 thin films. It is shown that I(4F9/2→4I15/2) increase with increasing Er3+ concentration. By studying the EL decay, the ratio of green to red emission vs applied voltage and EL efficiencies of 4F9/2 and 2H11/2+ 4S3/2 energy levels of ZnS:ErF3 thin films with different Er3+ concentration, we find that the increase of I(4F9/2→4I15/2) is due to the cross-relaxation processes occurred between Er3+ ions. The cross-relaxation rate increase with increasing Er3+ concentration, and results in the increase of I(4F9/2→4I15/2).
1988, 37 (10): 1626-1632.
doi: 10.7498/aps.37.1626
Abstract +
In some paramagnetic media, the effective field Hi which includes exchange interaction and external magnetic field, can cause the splitting of ground state energy level. In the region of the temprature T>Tc, the Curie temperature, there is certain probability distribution of electrons on two energy levels arised from ground state splitting. This induces the ground state energe level for double transition. It is proved by calculation according to this theory, there are several temperature characteristics for magneto-optical Faraday effect of the paramagnetic media. With the external magnetic field not too high, the ratio of the Verdet constant to magnetic susceptibility x is V/x = A(1+BT) in some media, or V/x = A(1 + B/T) in other media. It is also showed that both the real part θ′ and the imaginary part θ" of Faraday rotation are proportional to the effective field Hi, and with similar temperature character beyond the range of optical absorption.
1988, 37 (10): 1633-1639.
doi: 10.7498/aps.37.1633
Abstract +
The variational approach to two-body correlations in atoms proposed by Wilets et al, and developed by bresent authors is applied to treat the correlations of excited states of the atoms. The (ls)(nl)1,3L excited states of helium iseelectronic sequence, the (1s)2(2s)(nl)3L states of beryllium isoelectronic sequence and the (1s)2(2s)2(nl)2L states of boron have been calculated.The results show that these correlation wave functions have simple structure and are feasible in caloulation application. The accuracy of our method is very close to those of more complicated CI and 1/Z perturbation expansion methods.
1988, 37 (10): 1640-1645.
doi: 10.7498/aps.37.1640
Abstract +
Many optically pumped Li2 laser lines (874-912 nm) resulting from A1∑u+ atate to X1∑g+ state transition of molecular lithium were generated at the vapor temperature beyond 900℃. With a resonator, the laser output was increased by about 9 times. The vibrational and rotational quantum numbers for some laser lines were identified.
1988, 37 (10): 1646-1651.
doi: 10.7498/aps.37.1646
Abstract +
In this paper, the experimental procedures are presented for carburizing and boronizing the 20 steel surface using a CW CO2 laser with an output power of 500-2000 W modulated CW. We also give a comprehensive analysis about the phase structure, the phase morphology, the distribution profile of the hardness and the resistance to abrassion of the sample after laser treatment. The experimental results indicate that the microstructure, the mechanical properties and the chemical composition in the surface layer of material will basically change. Furthermore, a preliminary discussion of the strengthening mechanism of the penetrating element by laser irradiation is also presented.
1988, 37 (10): 1652-1657.
doi: 10.7498/aps.37.1652
Abstract +
The pump depletion is a severe problem which hinders the laser-plasma beat-wave accelerator concept from being practical. Starting with the weak relativistic equation of beat-wave excitation of electron plasma waves, we have derived the condition for eliminating the pump depletion in the frame moving with the light pulse for arbitrary pulse shapes. It is shown that the depletion can be eliminated by a phase jump of π at the center of the pump pulse and by the appropriate choice of initial plasma density detuning. The numerical calculation have yielded the dependence of the initial detuning on the pump intensity for square pump pulses, and have supported the methods used in this paper.
1988, 37 (10): 1658-1663.
doi: 10.7498/aps.37.1658
Abstract +
In the six Nd:glass laser facility, a multi-frame optical diagnostic system with a 0.63 μm, 50 ps (FWHM) probing beam is set up. We use this system to investigate the states of la-ser-produced plasmas by means of simultaneous measurements of interferometry and shadow-graphy or Faraday rotation. Moreover, we have used five-time-frame interferometry or sha-dowgraphy and streaked shadowgraphy in our experiments. The results such as electron density profiles and their evolution, inhomogeneous plasma jet structure and self-generated magnetic field are obtained.
BRIEF REPORT
1988, 37 (10): 1664-1667.
doi: 10.7498/aps.37.1664
Abstract +
Using the Anderson lattice Hamiltontan, we discussed the superconducting mechanism of high-Tc superconductors. The result show that the superconductivity may be induced by the hybrid Cooper pairs of electrons between the two bands of localized and delocalized states due to strong corrlations of electrons in the band of localized states.
1988, 37 (10): 1668-1671.
doi: 10.7498/aps.37.1668
Abstract +
In this paper, the experimental measurement and theoretical calculation of compressibility of La-Ba-Cu-O superconductor are presented, and its Bridgman's equation of stale is establised by using the experimental data.
1988, 37 (10): 1672-1677.
doi: 10.7498/aps.37.1672
Abstract +
In this paper, we present a two-region numerical analysis method for pellet ablation in plasma where Te≤5keV, as well as the analytic expressions of ablation variables, which conform with the results of our nemerical analysis. Our results show that the major shield region is pellet suface vaporizing layer rather than ablatant cloud and that the flow of ablatant is supersonic when Te≤5keV.
1988, 37 (10): 1678-1683.
doi: 10.7498/aps.37.1678
Abstract +
Making use of the stochastic model, we have studied the low-hybrid wave scattering by the density fluctuations in the edge-regions of Tokamak plasmas. The dispersion relation under consideration includes not only the E×B convective derivation term but also the electromagnetic correction term. The results show that the transmission coefficient decreases, whereas the reflection coefficient increases when the electromagnetic effect is taken into account.
1988, 37 (10): 1684-1689.
doi: 10.7498/aps.37.1684
Abstract +
In this paper we show that the abnormal phenomena near resonance are caused by the divergence of the electron orbits. The identification of the radiation mechanisms is also discussed.
1988, 37 (10): 1690-1693.
doi: 10.7498/aps.37.1690
Abstract +
This paper present the experimental records of the light emitting from heating lumines-cence at the back surface of aluminium foil or stepped targets, obtained by an optical ultra-fast speed streak camera. The target was irradiated by a focused high power laser beam with 500 J output energy in 1.2 ns FWHM pulse. The results showed that the degree of fllatness of the laser driven shock wave was obviously improved due to application of the special com-Lined lens. In these experiments the shock wave velocity in the step of aluminium target was obtained to be 17.6 m/ns, correspounding to shock wave pressure of 4.4 Mbar.
1988, 37 (10): 1694-1697.
doi: 10.7498/aps.37.1694
Abstract +
The fluorescent characteristic in Nd: YAG single crystal fibers has been investigated. One rod and four claded fibers produced with MPG process were tested, of which the diameters ranged from 41 micron to 120 micron with variations less than 0.5%. Excited by 300 milliwatt power laser at 0.6 micron, the fluorescence amplification at 1.06 micron was observed. The analysis predicted the condition and capability of superfluorescence.
1988, 37 (10): 1698-1702.
doi: 10.7498/aps.37.1698
Abstract +
A new computational method which can easily evaluate the relationship between the magneto-optic Kerr rotation angle θK and temperature T is presented. As a practical example, using this method, we have obtained the numerical solution for the preferential quadrilayer structure, the solution is in good accordance with the experimental results. On the basis of the best reading laser power derived by this method, the optimum signal to noise ratio of the optic disk can be obtained.
1988, 37 (10): 1703-1706.
doi: 10.7498/aps.37.1703
Abstract +
The influence of temperature on ordinary hard bubbles and their corresponding hard stripe domains in epitaxial garnet bubble films was investigated experimentally, A critical temperature T0, which is related to the parameters of bubble films, was found. When the testing temperature T0, the VBL chains in hard domain walls are not changed after temperature increasing and then decreasing. When T>T0, however, the VBL chains disappear, so that all of hard domains become soft. When VBLs in walls are compressed, the harder the domain, the lower its softening temperature. During softening, the way of VBL disappearance is a sudden break down of the whole chain.
1988, 37 (10): 1707-1714.
doi: 10.7498/aps.37.1707
Abstract +
The transformation method in reference [1] is extended to treat the lattice composed of different spin atoms (Sa=l, Sb= l/2), the ground state's spin structure, energy and phase boundary of the simply cubic lattice with ihird nearest neighbors, next nearest neighbors and nearest neighbors antiferromagnetic interaction haye been calculated in an arbitrary magnetic field. We conclude that the lattice possesses two antiferromagnetic spin structures and four subferromagnetic spin structures from the phase diagrams.
1988, 37 (10): 1715-1717.
doi: 10.7498/aps.37.1715
Abstract +
The results of the total energy calculation showed that in VA13 the tetragonal D022 phase (structure) is energetically favored as compared to the cubic L12 phase, this consists with experiment. In addition, the density of states at EF in D022 phase is two orders of magnitude smaller than that in the L12 phase.
1988, 37 (10): 1718-1728.
doi: 10.7498/aps.37.1718
Abstract +
A model on the Rayleigh-Benard problem of a non-ideal MHD flow in a sheared magnetic field is proposed and studied. A new set of nonlinear differential equations for the model bas been derived. Theoretical and numerical analysis shows that the set of equations implies a strange attractor with several novel features differing from Lorenz attractor and, in particular, the coexistence of all three routes to chaos in that model. Among the well-known models with these routes, so far, our system of equations is the unique one without any extrinsic periodic driving term. It exhibits more immediately the intrinsic stochasticity of deterministic nonlinear system. The stochastic motion and reconnection of magnetic field-lines, and the creation of magnetic islands are observed in numerical simulating of this set of equations.
1988, 37 (10): 1729-1734.
doi: 10.7498/aps.37.1729
Abstract +
We have found that some bowl-like compounds can form disordered crystalline phaseswhich have long-range positional order, with strong fluctuation in position and orientation. Their side chains are in a molten state. X-ray diffraction has shown that two homologues of hexaesters of cyclotricatechylene are stacked as triclinic system with space group of Pl. The parameters of a unit cell, density of the compounds, as well as expansion coefficient are obtained. The modelling of an unit cell is presented, which confirms the up and down asymmetry in the molecules, but there is no ferroelectricity macroscopically.
1988, 37 (10): 1735-1740.
doi: 10.7498/aps.37.1735
Abstract +
Fractal regions in a-Ge/Au bilayer thin films after annealing at different temperatures were investigated by TEM, and fractal dimensions were calculated. For 100℃ annealing, un-cleating positions are fewer, large tenuous scale-invariant regions formed with fractal dimension of 1.785±0.01, for 200℃ annealing, uncleating positions increased rapidly, besides thic- ker fractal region with fractal dimension of 1.818±0.008, many isolated island-like regions formed. After 300℃ annealing, only two kind of island-like regions formed with very different size. The relationship between crystallization of a-Ge film, condensation of Au film and mechanism of appearence of fractal region was discussed based on structural and quantitative analyses.
