Vol. 39, No. 2 (1990)
1990-01-20
GENERAL
1990, 39 (2): 169-176.
doi: 10.7498/aps.39.169
Abstract +
It is shown in this paper that the electromagnetic field yielding a semi-plane-symnmetric metric can be either plane-symmetric or semi-plane-symmetric. If it is plane-symmetric, then it must be a non-null electromagnetic field, while if it is semi-plane-symmetric, then it can be either null or non-null. The general solution of semi-plane-symmetric spacetimes yielded by semi-plane-symmetric sourceless null electromagnetic field is also given in this paper.
ATOMIC AND MOLECULAR PHYSICS
1990, 39 (2): 177-182.
doi: 10.7498/aps.39.177
Abstract +
The influence of adding KCI to silver colloid on light absorption of the colloid was studied and compared with that of adding pyridine to the colloid. It was found that the light absorption was increased due to the formation of an atomic cluster layer on the Ag particle surfaces caused by adding KCI, and that the original surfaces plasmon resonance absorption was reduced. At the same time, the linear-chain aggregation caused by adding KCI lead to an apparent red shift of the plasmon resonance absorption, which sometimes was difficult to observe. The influence of these changes on SERS was also discussed.
CLASSICAL AREA OF PHENOMENOLOGY
1990, 39 (2): 183-189.
doi: 10.7498/aps.39.183
Abstract +
The effects of transverse distribution of light field on CO2 laser instabilities are studied by means of light feedback. The phenomena of pulsing frequency shift and chaos in CO2 laser caused by light feedback are observed experimentally. The mechanism of laser instabilities resulting from the transverse distribution is discussed.
1990, 39 (2): 190-193.
doi: 10.7498/aps.39.190
Abstract +
Continuously tunable second harmonic generation of 294.8-282.5 nm was obtained by Q-switched YAG laser pumped Rh·6G dye laser in a 45°cut β-BaB2O4 (BBO) crystal. The output energy of the harmonic wave is about 8mJ around 285 nm. The continuously tunable output over the range of 230.8-223.2 nm was also obtained by the sum frequency mixing between the residual pump fundamental wave (1064nm) and the second harmonic wave of Rh 6G dye laser in an other 45°cut BBO crystal. The sum frequency output energy is about 120 μJ around 226 nm, the corresponding peak power is 12 kW. The key techniques of the sura frequency generation were indicated.
1990, 39 (2): 194-203.
doi: 10.7498/aps.39.194
Abstract +
A new method is presented for predicting the distribution of vector scattered fields of multilayer optical coatings. The scattering properties of film stacks with various interface cross-correlation models are discussed according to the statistical principles. The theory has been related to the familiar concepts of thin film optics, and simple results are obtained. It is shown theoretically that even though the optical parameters of the multilayer optical coatings are the same, the scattering losses can be quite different due to the different interface cross-correlations. Measurements of the scattered field distribution of optical films have also been made, and from them the interface cross-correlations of the multilayer optical films are determined according to the vector scattering theory.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1990, 39 (2): 204-211.
doi: 10.7498/aps.39.204
Abstract +
In ref. [I] , numerical experiment reveals scaled superstructures In the bifurcation diagram for the damped nonlinear drift-wave driven by a traveling wave. In this paper, it is shown that the resonance between the solution of driv en-damped equation and that of the unperturbed system is the cause of winding number bifurcation and hence of the superstructure. The scaling law for the wavenumbers and frequencies calculated accordingly is in agreement with the numerical results.
1990, 39 (2): 212-217.
doi: 10.7498/aps.39.212
Abstract +
In this paper, the research results of the relations between the excitation stage of linear ion Bernstein wave (IBW) and the edge ion density fluctuation, the discharge parameters of tokamak and the antenna position in KT-5B tokamak are presented. The experiments show that large edge ion density fluctuation will make it difficult to excite IBW, the ranges of discharge parameters for optimally exciting IBW are consistent with those for normal operation of KT-5B tokamak. We find that for our toroidal current antenna, there may exist two ways of excitation, i.e. direct excitation and excitation through the electrostatic mode conversion process.
1990, 39 (2): 218-224.
doi: 10.7498/aps.39.218
Abstract +
The effects of weakly felativistic trapped electrons on whistler instability in the magnetic-mirror configuration are studied. Using the simplified box model(1) the eigen equation is solved with perturbative approach including the weakly relativistic trapped effects. It is found that whistler instability can be driven by the anisotropic hot electrons, while relativisity increases the threshold value of instability and descreases the growth rate as well as makes the unstable modes shifting to low frequency.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1990, 39 (2): 225-230.
doi: 10.7498/aps.39.225
Abstract +
Double crystal diffractometer applied to measure SAXS is very satisfactory, since it has high resolving power and relatively small measure area. But for a long time it has not been used widely, because it has comparatively strong background which may cover the signal of SAXS. We point out that this background results from two kinds of its sources, one is the fluorescence come from the second crystal; the other is the effect of tail part of the rocking curye of crystal used. The contribution of the first source can be subtracted by a pulse height analyser. We present here a method that can subtract the effect of the tail part of rocking curve. Experiment domonstrates that this method is satisfactory.
1990, 39 (2): 231-236.
doi: 10.7498/aps.39.231
Abstract +
The one-dimensional incommensurate modulated structure of ankangite (Ba0.827(Ti5.827V2.294Cr0.053)O16), a mineral recently discovered in China, has been studied by electron diffraction. Its average structure belongs to tetragonal system and unit cell parameters of the average structure are a= 10.2?, c=2.96?. The modulated wave spreading along direction c has the wave length of λ = 2.30c. The features of electron diffraction patterns are analysed in detail. The possible mechanism of the incommensurate modulated structure in ankangite is discussed and a modulated structure model of vacancy-displacive type is proposed. The disorder structure caused by the difference among initial phases for displacement functions from place to place is discussed.
1990, 39 (2): 237-244.
doi: 10.7498/aps.39.237
Abstract +
RHEED intensity oscillations in the process of MBE growth of Ge and Si on Si (100) and Si (111) substrates were observed. It is revealed that a finite-thick buffer layer can improve the surface flatness of Si substrates, and the employment of lower growth rate or growth interruption procedure can improve tke crystal quality of epilayers. During the growth of Ge and Si on Si (100), a single atomic layer mode RHEED intensity oscillation was observed along either [100] or [110] azimuthal direction, which is due to the existance of double domain (2×1)+(1×2) reconstruction on the surface. During the growth of Ge on Si (111) substrates, RHEED intensity oscillation show a bilayer mode observed along [112] azimuth, but a non-uniform periodicity along [110] azimuth. The oscillations for continuosly growing Ge-on either Si (100) or Si (111) could exist up to an epilayer thickness of 6ML, which corresponds to the critical thickness of pseudomorphic growth of Ge on Si.
1990, 39 (2): 245-253.
doi: 10.7498/aps.39.245
Abstract +
Using the Tosi-Fumi pair potential, we have performed simulations of the cooling of molten salt, lithium chloride, at the rate about 5×1012 Ks-1 to study the glass transition and the structural and dynamic properties of the simulated supercooled liquid. It can be seen from our calculation that over the range from 498K to 298K, the peak of the radial distribution function is split into two subpeaks, the self-diffusion cofficient decrease rapidly and the distribution of bond angle has a high peak. So the simulated glass transition temperature should occur ac this range. At 298K the first coordination number of Li+ or Cl- calculated from the cumulative coordination number curve N(r) is about 4. The simulation indicates the existence of microscopic holes in melt and glass. The relationship between the temperature and the number of holes is discussed.
1990, 39 (2): 254-260.
doi: 10.7498/aps.39.254
Abstract +
Thermal annealing behavior of secondary defects in silicon implanted with MeV energetic boron ions has been studied. We snggest a new type of enhanced annealing effect of donble implantation, which can be used effectively to suppress or eliminate the secondary defects in such implanted silicon samples. The physical mechanism of the suppression and elimination processes is discussed.
1990, 39 (2): 261-269.
doi: 10.7498/aps.39.261
Abstract +
In this paper, with the assuption of effective lattice mode of coupling, a generalized theoretical expression of multiphonon relaxation rate has been derived by using quantum mechanical generating function method. An analytical rate expression is presented for high-order approximation case. Limitations of relaxation rate expressions in weak coupling approxamation given by Fong et al. with the quantum statistical method, and in weak coupling approximation and low temperature approximation given by Miyakawa et al. with quantum statistical method are pointed out. The dependence of the multiphonon relaxation rate on temperature, phonon. energy, energy gap and displacement parameter are also calculated.
1990, 39 (2): 270-277.
doi: 10.7498/aps.39.270
Abstract +
In this paper, we report the discussion on the nonlinear optical properties of an oxygen-covered Ag as well as the experimental studies with optical secondharmonic generation (SHG) in an ultrahigh vacuum system. The resulted SH signals are found to be very sensitive to the charge transfer between oxygen and silver. Based on the SHG measurement of oxygen adsorption dynamics, we seggest that the unmber of electrons donated to silver from the π-filled orbital might be more than that transfered from silver to the π* anti-bonding orbital of adsorbed oxygen molecules. Besides, the temperature programmed dissociation of adsorbed oxygen molecules was investigated, which could be explained in the framework of a simple model.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1990, 39 (2): 278-281.
doi: 10.7498/aps.39.278
Abstract +
The electronic structures of Al3Y in the three (DO19, Ll2, and DO22) phases were investigated using the allelectron total energy self-consistent LMTO method. The calculated results for total energy showed that the hexagonal DO19 phase is the most stable structure among these three phases, this is in agreement with experiment. Furthermore, it is found that the stability depends strongly upon the band filling of the bonding states and exhibits a inverse relationship with the density of states at EF.
1990, 39 (2): 282-288.
doi: 10.7498/aps.39.282
Abstract +
Ab initio calculations of optical-phonon deformation potentials (ODP)d30, d10 (val) and d10 (cond) on Λ-axis in Brillioun zone for the compounds GaAs and AlAs are reported. The study is based on a frozenphonon model and using the LMTO-ASA method with a frozen-potential approximation, in which the displacement of the empty sphere was considered +o match its atomic sphere partners. The validity of our method and results have been verified with the aid of calculations for wave-vector dependence of the ODPs on Λ-asix, the numerical test to the expressions about d0 VS d30 and d10 VS d10 (val) near Γ point and an extensive comprison with various calculations as well as the experiment.
1990, 39 (2): 289-295.
doi: 10.7498/aps.39.289
Abstract +
The existing theory points out that the soliton in polyacetylene only possess one electronic bound state-the mid gap state. Our work shows that, due to the electron interaction and the discrete atomic structure of polymer chain, the charged solitons have two bound states in the gap; one is a deep level, which is 0.2eV away from the midpoint of the gap; the other is a shallow level 0.06eV apart from the band edges. Our theory agrees with the photo-induced absorption in trans-(CH)x.
1990, 39 (2): 296-301.
doi: 10.7498/aps.39.296
Abstract +
The criterion of classification for three kinds of hard domains with lots of VBLS in their walls in garnet bubble materials is proposed. Their formation and static characteristics are described in detail and their typical pictures are shown. Considering the formation conditions of hard domains, it is reasonable to deduce that the increase of the number of VBLs in their walls leads to substantial change of their static characteristics.
1990, 39 (2): 302-311.
doi: 10.7498/aps.39.302
Abstract +
A new type of M?ssbauer spectroscopy-time-dependent M?ssbauer spectroscopy isproposed and realized on the basis of using two-step decay 119mTe→119Sb→119Sn.For the GaAs samples, implanted with dose of 110keV 119mTe + 1015 stable Te/cm2 and annealed at 600℃, the relative intensities of various lines of the M?ssbauer spectra have been measured as functions of ξ, a parameter being equal to ΦTe/ΦTo+a1 by definition ξ itself is determined from the annealing time ta, the initial time ti and the final time tf of the measurement of each spectrum. This kind of time-dependent M?ssbauer spectroscopy can be used to investigate the change of the environment of the probe atoms in solid. The lines of M?ssbauer spectra have been identified. The problem of the environment change of Te atom in GaAs after its decay into Sb and the mechanism of the non-substitutional Te have been discussed. Our experimental results are also compared with previous data taken from M?ssbauer spectra of 125Te and 129Te in GaAs.
1990, 39 (2): 312-318.
doi: 10.7498/aps.39.312
Abstract +
In this paper, the radiative transition probability, non-radiative transition probability, cross relaxation probability and other spectral parameters are calculated in detail. By considering three kinds of radiative processes, the fluorecent dynamic process is discussed, the relations between the fluorescent character and the concentrations of Er3+ ions are studied, and their laws are given.
1990, 39 (2): 319-324.
doi: 10.7498/aps.39.319
Abstract +
Based upon the binary collision approximation (BCA), the Monte Carlo methods are employed to study sputtering of multi-component amorphous targets. Total and partial sputtering yields, energy and angular distribution and the escape depth distribution of sputtered particles are given. The changes of surface concentrations are also studied The results indicate that the collisional effect may account for the preferential sputtering, which plays an important role in surface composition changes due to ion bombardment.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1990, 39 (2): 325-336.
doi: 10.7498/aps.39.325
Abstract +
By use of cluster variation method, a study of orderdisorder transition in A+2(B1/31B2/32)O3 system was carried out. Theoretical calculation indicated that the interaction energy parameter J had a great influnce on formation of both, the (B2/31B1/32)1/2 :B1/22 =1:1 mixed ordered domain and B1/31:B2/32= 1:2 domain, and predicted that it was more difficult to form the B1/31:B2/32= 1:2 full ordered domain relatively to the (B2/31B1/32)1/2B1/22 = 1:1 mixed ordered domain.
