Vol. 38, No. 12 (1989)
SPATIALLY PERIODIC STRUCTURES OF A FOURTH ORDER REACTION-DIFFUSION SYSTEM WITH DIFFUSION INSTABILITY
1989, 38 (12): 1901-1910. doi: 10.7498/aps.38.1901
Spatially periodic structures of a parameterized fourth order reaction-diffusion system with-diffusion instability, where the diffusion term is governed by Cahn-Hillard's generalized diffusion law, are studied by means of bifurcation theory. A criterion of bifurcation for generating ipatially periodic steady states from spatially homogeneous steady states is provided through stability and singularity analysis. The second order approximation of spatially periodic steady states. is obtained by singular perturbation technique. The theoretical results in this paper are in good accord ance with numerical results in  .
1989, 38 (12): 1911-1918. doi: 10.7498/aps.38.1911
In this paper, projection matrix method for solving soliton equations is described. Soliton transformation and breather transformation are derived. And the regularity of the solutions is proved in general.
CRYSTALLIZATION OF AMORPHOUS Nd3Fe81B16 ALLOYS AND ITS INFLUENCE ON MAGNETIC PROPERTIES AND M?SSBAUER SPECTRA
1989, 38 (12): 1919-1926. doi: 10.7498/aps.38.1919
Crystallization and its influence on magnetic properties and M?ssbauer spectra in the rapidly solidified amorphous Nd3Fe81B16 alloys are reported. The addition of 3at% Nd to FeB alloys raises the crystallization temperature from 435℃ for Fe81B19 to 523℃ for Nd3Fe81B16. After the crystallization at the optimal annealing condition the magnetic properties as permanent magnet were obtained to be: Br≈12kG, bHc = 2 kOe, and (BH)max≈8 MGOe, with room temperature seturation magnetization σs = 189 emu/g, remanence ratio σr/σs = 0.7 and intrinsic coercivity iHc = 2.15kOe. Comparing with widely used anisotropic BaFe12O19 ferrite, its Br and (BH)max is much higher. Therefore this material may be developed into a new cheap pe manent magnet. The influence of small addition of Nd on the physical properties of the alloys-are discussed. Based on the data from X-ray diffraction, M?ssbauer spectrocopy, SEM and magnetic measurments, the mechanism controlling the magnetization and demagnetization processes is thought to be domain wall pinning.
1989, 38 (12): 1927-1936. doi: 10.7498/aps.38.1927
The dynamic Stark effect on the dynamical behaviors of atom and squeezed state field in-two-photon processes is studied by a model consisting of an effective two-level atom with multiple levels and quantized field with single mode. The dynamic Stark effect will cause the decreasing of the revival amplitude and the shortening of the period of the atomic Rabi osoillation of inversion, and the increasing the speed of energy exchange of an atom with the field. This is favorable to the enhancement of the photon antibunching and the narrowing of the Poisson distribution of photons. However, it will make the squeezing of field to decrease, even disappear.
1989, 38 (12): 1937-1944. doi: 10.7498/aps.38.1937
The dynamic behavior of a hybrid optical bistability with two delayed feedback loops under the adiabatic approximation condition is studied. In this models, the system can be described by high dimensional mappings. Increasing input intensity while keeping the ratio of two time delays fixed at ω = 3/5, we observe transitions between three-frequency quasiperio-dicity and chaos. This result could be of importance in our understanding of turbulence.
1989, 38 (12): 1945-1950. doi: 10.7498/aps.38.1945
Using the two-photon resonance enhanced SHRS, FWM and OPSE processes in sodium vapour, the two sets of the UV coherent radiation in 230 nm-340 nm have been observed, and the characteristics of these UV radiation are presented and discussed.
1989, 38 (12): 1951-1957. doi: 10.7498/aps.38.1951
Excited molecular structure in gas phase usually consists of two types of energy states: Rydberg states with diffused molecular orbitals and valencetype excited states with rather localized molecular orbitals. Excitation from molecular inner-shell orbitals into the above-men-rioned excited orbitals leads to near-threshold structures. Based on the multiple-scattering self-consistent field theory, we have studied the molecular near-threshold structure. Our theoretical results are in good agreement with experimental measurements. We have also elucidated:(1) The dynaimcal interaction between the excited electron with the residual molecular ion.(2) Physical orgin of the shaperesonance, namely, as an anti-bonding state embedded in the continuum.
COHERENT STATES, SQUEEZED FLUCTUATION, AND RECOMBINATION RADIATION OF ELETRON-HOLE PAIRS IN SEMICONDUCTOR
1989, 38 (12): 1958-1967. doi: 10.7498/aps.38.1958
The production of Bose approximation coherent states and SU(2) coherent states of electron-hole pairs in semiconductor generated by coherent light excitation are discussed. Squeezed fluctuation and recombination radiation of electron-hole pairs are studied for these two cases. The second order coherence and distribution functions of electron-hole pairs are given. It is shown that the Bose approximation corresponds to the contraction of group SU(2) to the harmonic-oscillator group.
1989, 38 (12): 1968-1973. doi: 10.7498/aps.38.1968
The surface states of Al0.7Ga0.3 As(l00) were studied by ultraviolet photoelecton spectro-scopy. It was found that there exist two surface states on Al0.7Ga0.3 As (100) surface, which could be removed by the adsorption of 1500 L hydrogen. The evolution of these two surface states with thermal annealing was investigated. Combining with the experimental results of LEED and XPS, it was recognized that the damage of surface could be removed effectively by a thermal annealing at a temperature near 450℃, and a nearly perfect surface of A10.7Ga0.3 As(l00) could be obtained.
1989, 38 (12): 1974-1980. doi: 10.7498/aps.38.1974
Angle resolved ultra-violet photoelectron spectroscopy( ARUPS) and high resolution electron energy loss spectroscopy (HREELS) are used to investigate the surface states of GaP (111) surf aces prepared by ion bombardment and annealing. It is found that the intrinsic occupied surface states related to P atom dangling bonds are located at 0.6 eV below the valence band maximum, while the defect induced empty surface states are located at 1.1 eV above the valence band maximum (Γ point). A 1.36 eV band bending in surface region is induced by these empty surface states.
1989, 38 (12): 1981-1987. doi: 10.7498/aps.38.1981
The experimental method and facilities for studing surface and interface atomic structure by MeV ion scattering are described. The crystal preparation and cleaning procedure of Al (100) are presented. The MeV ion channeling and scattering experiments indicate the themal vibration amplitude of Al(l00) surface atom is 1.2-1.3 times greater than that of bulk atoms. The relaxation of Al(l00) first layer atom is less then -0.05?.
AN INVESTIGATION OF DENSITY OF GAP STATES IN AMORPHOUS SEMICONDUCTORS BY THERMOSTI-MULATED CONDUCTIVITY SPECTRA
1989, 38 (12): 1988-1995. doi: 10.7498/aps.38.1988
Determination of the density of states in the uper half of gap in a-Si:H film and a-Si:H/a-SiNx: H superlattices were obtained by a more comprehensive theoretical analysis of the thermostimulated comductivity. The results are consistent with that of Fritzsche's analysis. The main features of the two different analytical approaches and the correlation between maximnm chermostimulated current emission energy Em and quasi-Fermi level were discussed. The results show that the thermostimulated conductivity in a-Si: H should be analysed in weak recombination condition. In consequence, retrapping of the thermostimulated carriers can not be negleted. Theory of Gu et al. improves the analysis of measurement of thermostimulated conductivity.
AUGER ELECTRON SPECTROSCOPIC STUDIES OF INTERFA CE AND BURIED LAYER OF SOI STRUCTURE FORMED BY ION IMPLANTATION
1989, 38 (12): 1996-2002. doi: 10.7498/aps.38.1996
The chemical composition and interface structure of silicon on insulator (SOI) formed by O+ (200 keV, 1.8×l018/cm-2) or N+ (190 keV, 1.8×1018/cm-2) implanted into silicon have been investigated by using Auger electron spectroscopy (AES) with in situ sputtering. For SOI structure produced by O+ implantation and annealing at 1300℃ for 5 hours, the characteristic Auger spectrum for the interface between the top silicon layer and the buried oxide layer was measured and a chemical state of silicon was identified, whose major transition was at 85 eV, different from that of the bulk silicon or silicon in SiO2. This chemical state was also discovered in the buried oxide layer. For SOI structure produced by N+ implantation and annealing at 1200℃ for 2 hours, a nitrogenrich porous layer was observed in the buried nitride layer. For both SOI structures, the strong asymmetry of the two main interfaces was observed. These results are in agreement with the results of infrared absorption (IR) analysis and transimission electron microscopy (TEM) analysis. The detailed explanation of these results is also presented in this paper.
1989, 38 (12): 2003-2007. doi: 10.7498/aps.38.2003
Defects in photorefractive BaTiO3 crystal, obtained by the top seed solution growth method, have been studied by analytical electron microscopy. Thin foils containing inclusions for transmission electron micrsocopy (TEM) were prepared by ion milling the mechanically polished thin sections. Combining diffraction and electron energy loss spectroscopy in a TEM, the inclusions were identified as amorphous Ba-Ti-O and Ba6Ti17O40. Other microdefects which are only visible in the TEM have been identified as crystalline precipitates.
1989, 38 (12): 2008-2018. doi: 10.7498/aps.38.2008
Based on the BRST quantization, a quasi-free field theory for the Krichever-Novikov string on arbitrary genus Riemann surface has been given in analog to the Siegel approach to free closed string field theory. A non-purtubative formalism has also been suggested.
1989, 38 (12): 2019-2028. doi: 10.7498/aps.38.2019
In this article, a theory describing the normal state of the heavy-fermion alloys has been proposed based on the Yoshimorikasai model in the framework of slave-boson mean field theory by using the CPA method. The density of states (DOS) and its concentration dependences for the conduction electrons and strong correlated f-electrons in the heavy-fermion alloys are calculated self-consistently. The results we obtained not only reveal the process of the pseudo-gap formation in the DOS, but also give a reasonable explanation of the low temperature coherence effects in specific heat and thermoelectric power for the heavy-fermion alloys.
The thermal stability of the uniaxial anisotropies in Co86 Zr14 and Co91 Zr9 amorphous films prepared by rf sputtering are investigated through isothermal annealing in a static magnetic field. It is found that the stability is improved with increasing content of Zr. The relaxation curves have been fitted with calculated ones assuming the lognormal distribution of activation energy. The mean value of activation energy has been estimated at 2.5 eV for Co86 Zr14 and 1.7 eV for Co91 Zr9 films, respectively. The anisotropy increases with decreasing metal content, that can be explained by the precipitation caused by the nonmagnetic interaction in amorphous alloys.
A TEM STUDY OF CRYSTALLIZATION OF AMORPHOUS Ni-Zr ALLOY (Ⅱ)——TRANSITION AREA FORMED DURING CRYSTALLIZATION OF Ni-33at%Zr
1989, 38 (12): 2034-2038. doi: 10.7498/aps.38.2034
A transition area, which appears in the transformation from a metastable phase to a stable one during the crystallization of Ni-33at% Zr amorphous alloy, had been investigated by means of TEM. From the lattice image, it can be seen that the unstable phase corresponds to fringes with broad spacing or alternate between broad and narrow spacings, the stable phase corresponds to a single kind of fringes with narrow spacing, but for the transition area the arrangement of fringes with broad or narrow spacing is random and shows no regularity. In addition, for this area, the electron diffraction pattern exhibits no translation summetry. The pattern can be seen as one of the transformation process between the unstable phase and the stable one. Distributions of the diffraction intensities of the transition area are simulated by means of models with identical atomic planes but various packing spacings, the result agrees with the actual intensity distribution very well.
DETERMINATION OF DIFFUSION COEFFICIENT AND QUENCHING RATE COEFFICIENT OF METASTABLE N2 MOLECULES N2(A3∑u+) USING TOWNSEND DISCHARGING
1989, 38 (12): 2039-2043. doi: 10.7498/aps.38.2039
The diffusion coefficient Dm and quenching rate coefficient Kq of metastable nitrogen molecule N2(A3∑u+) in pure N2 has been determined using Townsend dischaging. The values of Dm of 128 cm2/s and KN2 of 8.1×10-19 cm3/s were obtained respectively.
1989, 38 (12): 2044-2048. doi: 10.7498/aps.38.2044
The laws with which the state vector of the two-photon Jaynes-Cummings model varies with the time are studies by means of the time-evolution operator. The statistical properties of atoms are discussed. The atomic squeezing effects are revealed.
1989, 38 (12): 2049-2053. doi: 10.7498/aps.38.2049
An analysis is given for multilens optical resonators. Dynamic characteristics of beam parameters for multilens resonators are analyzed. A new concept of compensating the effecus, caused by the change in thermal focal length is presented. Hence, a new type of thermal stable resonators——controlled model resonators also called soft resonators is presented.
1989, 38 (12): 2054-2058. doi: 10.7498/aps.38.2054
The transverse relaxation time measurement for Raman mode by Raman enhanced nonde-generate four wave mixing (RENFWM) has been made in the frequency domain. We get spectra of RENFWM that the nonresonant background is suppressed. The transverse relaxation time of Raman mode in benzene and methlybenzene is obtained as 1.5 ps and 2 ps respectively.