Vol. 39, No. 12 (1990)
1990, 39 (12): 1863-1869. doi: 10.7498/aps.39.1863
The desciption of globally regular SchwarzschiId space-time in a Newman-Penrose formalism is given in the Schwarzschild coordinate and the Kruskal coordinate respectively. It is shown that this space-time has the global algebraic property. Globally it is of Petrov type-D. The behaviours of tetrad components of the Weyl tensor, the spin coefficients and null vectors are also discussed.
ATOMIC AND MOLECULAR PHYSICS
1990, 39 (12): 1870-1876. doi: 10.7498/aps.39.1870
35 autoionising energy levels of Ne atom in ns＇(n = l5-35) and nd＇(n = l3-30) series have been determined experimentally with pulsed electric field optogalvanic spectroscopy. The ionization limit of the ns＇ and nd＇ series was found by parametric fitting and the quantum defects of all these levels were calculated. Instead of the direct discharge, pulsed electric field was used in the experiment, to eliminate Stark effects in the optogalvanic spectroscopy.
CLASSICAL AREA OF PHENOMENOLOGY
1990, 39 (12): 1877-1886. doi: 10.7498/aps.39.1877
A fluctuation model is suggested in this paper for the mode-locked laser incorporating a nonlinear mirror with intensity dependent reflection coefficient. Computer simulation with this model is conducted for varied parameters of Nd: YAG lasers and for two kinds of nonlinear crystal (KTP and KDP). The optimum parameters and conditions under which perfect mode-locking will be achieved are predicted according to the simulation calculation.
1990, 39 (12): 1887-1892. doi: 10.7498/aps.39.1887
By means of the density matrixs in forms of Bloch equations which are coupled with Maxwell equations, we treated propagation effect of coherent pulse in the strong loss medium. Both pulse evolution and its influence on the medium have been studied. We observed the special transient coherent phenomena of pulse in the strong loss medium which include the stepwise decreasing of pulse area and periodic oscillation of number of spatial ionized particles.
1990, 39 (12): 1893-1899. doi: 10.7498/aps.39.1893
In this article, we consider the optical second harmonic nonlinearity (corresponding to x(2)) associated with intersubband transitions in a doped parabolic multiquantum well structure, due to the anharmonic correction. The calculation indicates that the x(2)(2ω) is larger than that of the bulk GaAs by 1 to 2 orders of magnitude, and the resonant transition frequencies are in the middle infrared region
1990, 39 (12): 1900-1907. doi: 10.7498/aps.39.1900
Based on the instability criterion of semi-classical Maxwell-Bloch equations of single-mode laser with an injected signal, we investigated the instability of this system In. particular, we examined the global structure of Hopf instabiliy domain in the entire parameter space and derived the boundary of this domain analytically. We also found a full hysteresis loop between the bistable states of the output laser intensity in the active cavity case and discussed the condition of occurance of such phenomenon.
The influence on the stress field in the vicinity of a crack tip due to a round inclusion is investigated. The antiplane shear problem is solved. After the classical stress field and stress strenth factor are obtained, the nonsingular nonlocal stresses in the vicinity of crack tip is obtained. The application of the solution is discussed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1990, 39 (12): 1915-1920. doi: 10.7498/aps.39.1915
A collisional-radiative numerical model is developed for studies of radiative losses and ion abundances in aluminum plasmas. Atomic processes such as collisional ionization and recombination, collisional excitation and dexcitation, radiation recombination, and spontaneous radiation are included. The dynamic results of ion abundances, radiation losses are discussed under the approximation of constant ion density and optically thin condition.
1990, 39 (12): 1921-1927. doi: 10.7498/aps.39.1921
We use a new method to measure electron density in the boundary layer of plasma, which is based on the fluorescence resulting from the collision of electron and lithium atom. We observe the fluorescence signal of lithium atom at 6708?(2P0-2S) with both CCD-camera and S20 photo-multipliers simultaneously. From the received radial intensity distribution, we deduce the radial distribution of electron density.
1990, 39 (12): 1928-1936. doi: 10.7498/aps.39.1928
In accordance with the experiment results of the tristable phenomena in argon discharge plasma in a double plasma device, the related semiclassical theory based on the fundamental physical processes, such as ionization, recombination, excitation and deexcitation, are established.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1990, 39 (12): 1937-1944. doi: 10.7498/aps.39.1937
The Reflection High Energy Electron Diffraction (RHEED) intensity oscillations under different angles of incidence and azimuths during Si(111) molecular beam epitaxy have been studied. The phase of intensity oscillation and initial transient response change dramatically with the angles of incidencl if the observation is carried out along  azimuthal direction, but vary little when observed along  azimuth. From the measurement results of RHEED specular beam rocking curve, we believe that, the characteristics of RHEED intensity oscillation as a function of electron diffraction condition, indicate the existence of two different seattering processes: coherently elastic diffraction beam oscillation and inelastic or diffuse scattering beam oscillation. This can be explained only by the electron multiple scattering mechanism. The origin of initial transient is also discussed.
1990, 39 (12): 1945-1951. doi: 10.7498/aps.39.1945
The growth dynamical processes of Si(111) molecular beam epitaxy under different growth temperature are studied by RHEED intensity oscillations. The Si(lll) epilayer grew in a "step flow" mode at the temperature above 520℃(growth rate 0.02 nm/s), and in a "2D nucleation" bilayer mode at temperature range between 520℃ and 420℃. Below 380℃, even at room temperature, the growth is still in a bilayer mode. The RHEED intensity oscillation shows a monoatomic layer mode during the initial stage of growth, which is believed due to the superposition of two kinds of oscillations originated from coherent elastically scattering and incoherent scattetring or surface diffuse scattering.
1990, 39 (12): 1952-1958. doi: 10.7498/aps.39.1952
The coadsorptive properties of some small molecules adsorbed on Pd(100) surface are investigated by taking the tight-binding model and the one electron approximation. The results show that (1) the indirect interaction between the two admolecules (or adatoms) on Pd (100) surface has an oscillatory behaviour with the decrease of the coupling strength between these adsorbates and the substrate, and (2) the existence of O2 or H2 affects the dissociation of NO on Pd(100). In addition, some adsorptive structures are derived from adsorbate-ad-sorbate indirect interactions. These results are compared with experimental results.
1990, 39 (12): 1959-1964. doi: 10.7498/aps.39.1959
By means of monitoring with the reflection high energy electron diffraction (RHEED) -and its intensity oscillations, the GaSb/AlSb/GaAs strained layer heterostructures have been suc-cessfully grown on semi-insulating (100) GaAs substrates by molecular beam epitaxy (MBE) The RHEED patterns show that the GaSb surface grown under Sb-stabilized condition has C (2×6) structure and the AlSb surface has (1×3) Sb structure. We observed and recorded the RHEED intensity oscillations during the growth of GaSb and AlSb. Using the information provided by the RHEED intensity oscillations, we successfully prepared a GaSb/AlSb super-lattice with 10 periods. The transmission electron micrograph shows the interfaces in the su-perlattice are sharp and planar. If the AlSb buffer layer is thick enough under a proper growth condition, a high-quality GaSb epitaxy will be grown on SI GaAs substrate. The full width at half maximun (FWHM) of the peak corresponding to the GaSb epilayer in double-crystal X-ray diffraction rocking curve is less than 300 seconds. Undoped GaSb is p-type with carrier concentration of 2.12×1016 cm-3 and mobility of 664cm2/V·s at room temperature.
PREPARATION OF DIAMOND FILMS BY DC ARC DISCHARGE AND IN SITU MEASUREMENTS OF THE PLASMA BY OPTICAL EMISSION SPECTRA
1990, 39 (12): 1965-1969. doi: 10.7498/aps.39.1965
High quality diamond films have been rapidly synthesised by the DC arc discharge plasma CVD in a hydrogen-methane mixture gas. The properties of the films are tested and analyzed by scanning electron microscopy, X-ray diffraction and Raman spectra. In order to find out the growth mechanism of vapor deposited diamond, in situ optical emission spectra of plasma under practical growth conditions are measured. It is found that the key factor of rapid growth diamond film is the presence of a large number of atomic hydrogen in the plasma.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1990, 39 (12): 1970-1981. doi: 10.7498/aps.39.1970
This paper introduces two-exciton squeezed states. For the two cases of "non-Bose" and Bose approximations of one-exciton, the squeezings and the second correlations of quantum and space correlated pairs of excitons, and the squeezings of its recombination radiations are discussed. It is shown that, in these two cases, the Bose approximations of the two-exciton correspond to the contractions of group SU(2) and group SU(1,1) to the group of harmonic oscillator, respectively. The influences of the contractions on the squeezings and correlations of the two-exciton are also given.
1990, 39 (12): 1982-1988. doi: 10.7498/aps.39.1982
The B depth profiles in B-doped a-SiC: H/undoped a-Si: H heteroiunctions have been measured by utilizing the nuclear reaction 11B(p, α)8Be. From the change of B depth profiles, we estimate the coefficients of B diffusion in a-Si:H during preparation and post-deposition annealing. The behaviors of electrically activated B diffusion have also been investigated by conductivity measurements. Based on the recent studies of thermal equilibrium defects in a-Si: H, a simple discussion on the mechanism of B diffusion in a-Si:H is presented in this paper as well.
The work-function change of potassium on the Cu(111) surface was studied. The work-function change was measured by a Kelvin probe. The coverage of potassium on the surface was determined by AES. Maximum work-function change Δφmax=3.14 eV. Initial dipole moment p(0) = 7.0 Debye, The minimum work-function occurs at the coverage θmin= 0.18. The result of this work is consistent with that of the jellium-slab model.
1990, 39 (12): 1994-1998. doi: 10.7498/aps.39.1994
The electronic structure of Nd2CuO4 has been calculated self-consistently by WLAPW method. Because of the interactions (hybridization) between the electrons in the localized Nd 4f bands and those in the conduction band, a≈4 states/eV. cell DOS peak of the Cu-0(1) dp a band is presented at 0.18 eV above the Fermi energy, which may be used as a possible interpretation of the superconducting transition in Nd2-xCexCuO4 with x.
1990, 39 (12): 1999-2004. doi: 10.7498/aps.39.1999
By measuring magnetization curves of polycrystalline Tl2Ba2Ca2Cu3Oy superconductor, magnetitudes of the hysteresis against temperature T and applied field Ba have been obtained. Using the critical state equation, we have got an effective pinning force which varies with temperature and field and results from both contributions of winklinks and intragrain pinning. Peak effect of the effective pinning force has been found, and the peak moves to higher fields with temperature dropping. The peak effect is considered to be the results of two pinning mechanisms, which have different field relations. Finally, some discussions about the results are made.
1990, 39 (12): 2005-2010. doi: 10.7498/aps.39.2005
The compositionally modulated amorphous films FeSi/Si have been prepared successfully. Systematically varying the thickness dm of the FeSi layers with fixed thickness of Si layers, it is shown that the saturation magnetization Ms decreases monotonously with decreasing dm. This basically is the contribution from the dead layer effect. The thickness of dead layer at OK is about 5.8?. With decreasing dm, the modulated films transit from three dimensional magnetism to two dimensional one gradually. The expressions of this transition are the appearances of low magnetic and nonmagnetic hysteresis effect, the linear Ms(T)-T relations and the monotonous decreasing of Curie temperature Tc. Tc satisfies the equation: △Tc∝dm-1, where λ=1.6.
1990, 39 (12): 2011-2018. doi: 10.7498/aps.39.2011
In this article, we investigate the properties (transition frequency, bandwidth, and dipole transition moment) of intersubband optical transitions by using the new general form of the Kronig-Penney model developed recently. The theoretical results are in good agreement with our experimental measurements of infrared absorption in a GaAs/AlxGa1-xAs superlattice.
1990, 39 (12): 2019-2024. doi: 10.7498/aps.39.2019
It is very important to evaluate the reflection of low energy ion from a surface of solid for understanding the interaction between plasma and the first wall in a fusion reactor. When ion energy is lower than 1 keV, the influence of the surface barrier of solids on ion reflection gradually becomes important. In the present paper, the influence of the surface barrier of soids on ion reflection has been evaluated by extending the bipartition model for light ion transport to the case of the boundary with a rectangular surface barrier. Our computational results have shown that surface barrier can remarkably reduce the ion reflection coefficient, when ion energy decreases down to less than 10 times surface potential energy of the solids.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1990, 39 (12): 2025-2028. doi: 10.7498/aps.39.2025
The chemisorption energy of hydrogen on ZnO/Ni composite substrate is investigated using the Green function method and the complex-energy-plane integration approach. The tight-binding approximation is employed to model the semiconductor ZnO by a finite chain of alternating s- and p-orbitals, while the semi-infinite metal Ni is represented by a linear chain of d-orbitals. The impurity effect on the chemisorption energy is evaluated. The calculation shows that: (1) the chemisorption energy is a monotonously decreasing function of the ZnO thickness; (2) the presence of impurities Cu and Pt (Co and W) can weaken (strengthen) the chemisorption process and (3) the impurity effects are most significant when the impurity is closest to the nickel surface.