Acta Physica Sinica
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Acta Physica Sinica  
  Acta Physica Sinica--1997, 46 (10)   Published: 15 October 1997
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CLASSICAL AREA OF PHENOMENOLOGY

ABSORPTION AND SCATTERED LIGHT OF GOLD DISKS IRRADIATED WITH 0.351μm LASER LIGHT

LIU SHEN-YE, TEN HAO, DING YONG-KUN, DING YAO-NAN, SU CHUN-XIAO, JIN GEN-ZHI, ZHANG HAI-YING, CHEN YU-TING, ZHENG ZHI-JIAN, TANG DAO-YUAN
Acta Physica Sinica. 1997, 46 (10): 1917 doi: 10.7498/aps.46.1917
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The experiments used the “Xingguang Ⅱ” laser facility to irradiate gold disks at some chosen angle of incidence. In this paper, we report the absorption and angular distribution of scattered lights of 0.351μm laser light by Au disks. The experiments have shown that the absorption by Au disk is higher than that irradiated with 0.53 or 1.05μm laser light. The angular distribution of scattered lights proves that scattered lights include stimulated Brillouin scattering and specular reflection from critical surface. Based on inverse bremsstrahlung absorption, the absorption obtained by simulation agrees with the experimental results.

DETAILED BALANCE AND ENTROPY FOR A TWO-LEVEL ATOM IN A SQUEEZED VACUUM VIA DEGENERATE TWO PHOTON PROCESSES

FENG XUN-LI, HE LIN-SHENG
Acta Physica Sinica. 1997, 46 (10): 1926 doi: 10.7498/aps.46.1926
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Using the principle of detailed balance and the evolution of entropy, the stability of a two-level system coupled to a squeezed vacuum via degenerate two-photon processes is investigated. We find that the stability of the system depends on the squeezing parameter M of squeezed vacuum. When |M| is small, the system is unstable, but when M is a very large real number, the system is driven to a stable state but far from equilibrium.

OFFAXIAL GAUSSIAN WAVE

ZENG XIAO-DONG, LIANG CHANG-HONG, AN YU-YING
Acta Physica Sinica. 1997, 46 (10): 1932 doi: 10.7498/aps.46.1932
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Based on a rigorous far field solution of the Helmholtz equation, a new method to describe the propagation of the offaxial Gaussian wave is presented. The amplitude and phase distribution, beam spot size, divergence angle, and the relation of the conservation of energy are discussed. It is found that for any Gaussian source the maximum divergence angle is shown to be 65.5.

COMPUTER SIMULATION OF THE THERMAL FLOW INSIDE THE HIGH PRESSURE CELL(Ⅰ) EQUATIONS AND METHODS OF SOLUTION

SUN ZONG-QI, XU JI-AN, XIE HONG-SHEN
Acta Physica Sinica. 1997, 46 (10): 1938 doi: 10.7498/aps.46.1938
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A two-dimensional approximation with axisymmetry was used to deal with the thermal conduction inside the high pressure cell . A numerical method, using a microcomputer, to obtain the static and non-steady distribution of temperature was given. The error of calculation in this method was estimated and an approximate analytical formula for the static distribution of the temperature was also given.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

INVESTIGATION OF THE STRUCTURES OF ZnTe/GaSb BY X-RAY TRIPLE-AXIS SCATTERING AND CRYSTAL TRUNCATION ROD

LI CHAO-RONG
Acta Physica Sinica. 1997, 46 (10): 1953 doi: 10.7498/aps.46.1953
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The structures of ZnTe/GaSb, grown by molecular beam epitaxy under different conditions, were investigated by X-ray triple-axis scattering and crystal truncation rod. The sample annealed under Zn flux from surface cleaning temperature to growth temperature had clear interference fringes in the crystal truncation rod scan profile, while the sample annealed under Te flux shows no interference fringes in the crystal truncation rod. Reciprocal space mapping around the symmetrical diffraction reciprocal point 004 and asymmetrical diffraction point 115 showed that the ZnTe epilayers were fully strained to the substrate. Both two-dimensional reciprocal space mapping and transverse scan along direction showed that the sample annealed under Te flux had strong and broad diffuse scattering in this direction. This was attributed to the Ga2Te3 formation at the interface. This interfacial phase would enhance the diffuse scattering, blur the interference fringes and roughen the surface and interface. The epilayer thickness was accurately determined to be (210±1)nm by theoretical calculation of the experimental profiles. The surface roughness of the sample annealed under Zn flux, (2.2±0.2)nm, was smaller that of the sample annealed under Te flux, (3.7±0.3)nm.The lateral correlation lengths of the samples annealed under Zn flux and Te flux are (420±10)nm and (30±5)nm,respectively.

ORDER PARAMETER AND NMR RELAXATION OF THERMOTROPIC LIQUID CRYSTAL CPHOB

MENG QING-AN, HU CHUAN-MIN, CAO QI-JUAN, LI ZI-RONG
Acta Physica Sinica. 1997, 46 (10): 1961 doi: 10.7498/aps.46.1961
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The proton magnetic resonance spectra of 4-cyanophenyl 4′-hexyloxy benzoate (CPHOB) were measured from room temperature to 380K. It was found that the transition temperature from solid to nematic phase was Tsn=347K, and the transition temperature from nematic phase to isotropic liquid Tni=359K. The temperature dependence of its order parameter was evaluated. Its mechanism of proton spin lattice relaxation was discussed.

SCANNING TUNNELING MICROSCOPIC OBSERVATION OF GRAPHITE SURFACE DAMAGE INDUCED BY GOLD IONS BOMBARDMENT(Ⅱ)

WANG YU-GANG, KANG YI-XIU, ZHAO WEI-JIANG, YAN SHA, YAN JUN-JUE, YANG WEI-SHENG, ZAI PENG-JI, TANG XIAO-WEI
Acta Physica Sinica. 1997, 46 (10): 1965 doi: 10.7498/aps.46.1965
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The individual damage on high oriented pyrolytic graphite surface induced by gold ions of 530keV—4.5MeV was studied with scanning tunneling microscope. The hillock-like damage was observed and measured and then the average diameters of the hillocks were obtained. In terms of a modified nonlinear thermal spike model, the diameters of the damage were calculated and the results fit well with the experimental data. The possible mechanism of damage formation is discussed.

PHASE TRANSITION AND NESTING IN LOW DIMENSION

LING FAN, CHEN XIAO-BING, FU RONG-TANG, SUN XIN, Y. KAWAZOE
Acta Physica Sinica. 1997, 46 (10): 1972 doi: 10.7498/aps.46.1972
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The nesting of the Fermi surface in a two-dimensional (2D) system is not perfect, which is distinctly different from one-dimensional system. The nesting deviation can heavily suppress the instability of 2D system. In this paper, the effect of the nesting deviation on the Peierls transition is quantitatively studied, and the limit for the nesting deviation, beyond which the Peierls transition is destroyed, is determined. Such a behavior is favorable to get the superconductivity.

STRESS ON THE Ni,Pd AND Pt SURFACES

FAN XI-QING, WAN JUN, SHEN SAN-GUO
Acta Physica Sinica. 1997, 46 (10): 1978 doi: 10.7498/aps.46.1978
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The semiempirical modified embedded atom method has been applied to calculate the surface stress on the low index surfaces of fcc metals Ni,Pd and Pt,and the results are in agreement with that of the first principle calculation.The surface stress on fcc(110) surface along the [110] direction is about twice as large as in the [001] direction;and this indicates that the anisotropy of the surface stress is a characteristic of (110) surface of fcc metals.In addition,the magnitudes of the surface stresses on Pd and Pt(100) surfaces have been predicted.

STUDY OF THE DIAMOND FILMS WITH HIGH THERMAL CONDUCTIVITY

GU CHANG-ZHI, JIN ZENG-SUN, Lü XIAN-YI, ZOU GUANG-TIAN, ZHANG JI-FA, FANG RONG-CHUAN
Acta Physica Sinica. 1997, 46 (10): 1984 doi: 10.7498/aps.46.1984
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The scattering of phonons as main factors infuencing the thermal conductivity were analized theoretically. The thermal conductivity of diamond films was measured by means of the photothermal deflection method with an error of 5%. The effects of methane concentration and grain orientation on thermal conductivity of diamond films were studied. The results showed that (100) oriented diamond-films deposited by microwave plasma chemical vapour deposition method under low methane concentration have higher thermal conductivity.

KINETICS AND SCALING BEHAVIOR OF REACTION PERCOLATION BALLISTIC SURFACE GROWTH

ZHU XIAO-BIN, WANG WEI
Acta Physica Sinica. 1997, 46 (10): 1990 doi: 10.7498/aps.46.1990
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The kinetics and scaling behaviors of reaction-percolation ballistic surface growth with two kinds of particles A and C is investigated. When the probability of particle C is zero, i.e. q=0,the deposition is the traditional ballistic deposition of single particle. When the probability is not zero,i.e.q≠0, in 2+1 dimensions and 3+1 dimensions, the morphological structural transitions are observed. When q approaches the threshold, at which the growth will stop, there is a scaling behavior for the growth velocity, which can be interpreted by the percolation theory.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

CALCULATION OF ELECTRONIC STATES OF THE CdTe(110) RELAXED SURFACE

JIA YU, FAN XI-QING, MA BING-XIAN
Acta Physica Sinica. 1997, 46 (10): 1999 doi: 10.7498/aps.46.1999
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By using the method of phenomenological scattering thoery,we have calculated the electronic structure of the CdTe(110) relaxed surface.The results are in good agreement with the experiments and other calculations.By analyzing the results we have discussed the origin of relaxation of CdTe(110) surface.

QUANTUM FLUCTUATION OF MESOSCOPIC CIRCUIT IN SQUEEZED VACUUM STATE

WANG JI-SUO, SUN CHANG-YONG
Acta Physica Sinica. 1997, 46 (10): 2007 doi: 10.7498/aps.46.2007
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Starting from equation of motion of an active LC circuit,the quantum fluctuations of the charge and current in the mesoscopic circuit (LC circuit) in the squeezed vacuum state are investigated.

CALCULATION OF CRITICAL LAYER THICKNESS BY TAKING INTO ACCOUNT THE THERMAL STRAIN IN Si1-xGex /Si STRAIN LAYER HETEROSTRUCTURES

HUANG JING-YUN, YE ZHI-ZHEN, QUE DUAN-LIN
Acta Physica Sinica. 1997, 46 (10): 2010 doi: 10.7498/aps.46.2010
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Effect of thermal strain on growth of SiGe strained layer on Si was analysed.Formulae for critical layer thickness were obtained by considering thermal strain in energy balance under the assumption of screw dislocation energy density equal to the sum of areal strain energy density and thermal strain energy density.The relationship between the thermal expansion coefficient associated with thermal strain and Ge content x was linear.The results are in good agreement with the experimental results reported.

INVESTIGATION OF GROWTH MECHANISM OF NANOCRYSTALLINE SILICON THIN FILMS PREPARED BY HOT-FILAMENT CHEMICAL VAPOR DEPOSITION

CHEN GUO, GUO XIAO-XU, ZHU MEI-FANG, SUN JING-LAN, XU HUAI-ZHE, HAN YI-QIN
Acta Physica Sinica. 1997, 46 (10): 2015 doi: 10.7498/aps.46.2015
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The nc Si∶H thin films were prepared by hotfilament vapor deposition.The effect of gas pressure,-high H2 dilution and substrate-to-filament distance on deposition rate,the formation and structure of nc-Si∶H films was systematically studied.The structure of nc-Si∶H was determined using Raman scattering and X-ray diffraction.The temperature distribution was calculated;the travel of radicals evaporated from the filament and the gas-phase reaction were discussed in detail.The results were in agreement with the measurement.

OPTIMIZATION OF Tc IN EPITAXIAL GdBaCuO SUPERCONDUCTING THIN FILM BY INVERTED CYLINDRICAL SPUTTERING

LI YAN-RONG, LIU XIN-ZHAO, XU JIN, J.GEERK, R.SMITHY
Acta Physica Sinica. 1997, 46 (10): 2023 doi: 10.7498/aps.46.2023
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Thin films of GdBaCuO(GBCO) compound have been deposited in situ onto LaAlO3 single crystal substrates by inverted cylindrical sputtering.The variation of superconductive properties of the thin films with the substrate temperature and sputtering pressure has been systematic investigated.By the optimization of deposition parameter,high quality c-axis epitaxial GBCO thin films of Tc0>92K were reproducibly grown at the substrate temperature of 720—820℃ with a low deposition total pressure (40Pa).The Tc0 of the best sample is as high as 93.2K.Only by changing the target composition into GdBa2Cu4Oy (Gd124),was it observed that the samples always contain some a-axis oriented films,impling that excess copper would favour a-axis growth in thin films,and the Tc of the samples is lower than that with Gd123 target.The superconductivity of the thin films under high substrate temperature was clearly improved by the procedure of special post oxygenization at 400℃ in ozone atmosphere.These results are very useful to further prepare large area thin films of GBCO.

CRITICAL BEHAVIOR AT THE SURFACE OF A SEMI INFINITE MIXED SPIN ISING SYSTEM WITH SURFACE RANDOM FIELD

GAO ZHAN, WANG ZHEN-LIN, XU JIAN-HONG
Acta Physica Sinica. 1997, 46 (10): 2029 doi: 10.7498/aps.46.2029
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In this paper,a renormalization group scheme within the framework of the mean field theory is used to investigate the critical behavior at the surface of a semi infinite Ising system with mixed spins,i.e.S=1 at the surface and σ=1/2 in the bulk.The effects of a random field on the surface phase diagrams are obtained.

NONLINEAR EXCITATIONS IN ONE DIMENSIONAL HEISENBERG FERROMAGNETIC CHAIN WITH BOND ALTERNATION

ZHU SHAN-HUA, HUANG GUO-XIANG, XU ZAI-XIN
Acta Physica Sinica. 1997, 46 (10): 2036 doi: 10.7498/aps.46.2036
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About the one-dimensional Heisenberg ferromagnetics chain with bond alternation,research results show,in first-order approximation,that (1) magnon gap solitons (with the vibrating frequency lying in the gap between magnon frequency band) and resonant kinks (with the vibrating frequency lying in the magnon frequency band) are found; (2) an instrinsic localized mode (with the vibrating frequency being above the magnon frequency band) is impossible.

COMPARATIVE STUDY OF STRUCTURAL AND MAGNETIC PROPERTIES OF Co/Cu MULTILAYERS MADE BY MBE AND SPUTTERING

ZHAO HONG-WU, BIE QING-SHAN, DU JUN, LU MU, SUI YUN-XIA, ZHAI HONG-RU, XIA HUI
Acta Physica Sinica. 1997, 46 (10): 2047 doi: 10.7498/aps.46.2047
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The structural and magnetic properties of Co/Cu multilayers prepared by molecular beam epitaxy(MBE) and sputtering were investigated and compared with each other.It was found that the well defined layered structures existed in both samples,and the former was epitaxial single crystalline;while the latter was textured polycrystalline.Ferromagnetic resonance study showed the existence of a six-fold symmetry in the film plane,revealing the perfect in-plane structure of MBE samples.Giant magnetoresistance and its oscillation with the Cu thickness were found in sputtered samples.On the contrary,the magnetic resonance of MBE samples is smaller,about 7% for the second peak position.It is assumed that the superparamagnetic structure may be formed at interfaces in MBE samples which results in the different magnetic-field-dependent behaviors of magnetoresistance and- magnetization.

TEMPERATURE DEPENDENCE OF PERMEABILITY FOR Fe-Cu-Nb-Si-B ALLOY

WANG ZHI, HE KAI-YUAN, YIN JUN, ZHAO YU-HUA
Acta Physica Sinica. 1997, 46 (10): 2054 doi: 10.7498/aps.46.2054
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The correlation between initial permeability μi and temperature T(μi-T curve) for the Fe73.5Cu1Nb3Si13.5B9 alloy annealed at 300—610℃ was investigated.Three types of μi-T curve were observed. The corresponding annealing temperatures are (1)Ta≤460℃,(2) 480℃≤Ta≤580℃,(3) 590℃≤Ta≤610℃.The phase structures of the alloy corresponding to the three types of μi-T curve were analysed and the mechanisms for the changes of μi with T were also discussed.

A NEW METHOD FOR POST TREATMENT OF POROUS SILICON:SULFUR PASSIVATION BY MICROWAVE PLASMA ASSISTANCE

LIU XIAO-BING, XIONG ZU-HONG, YUAN SHUAI, LIAO LIANG-SHENG, HE JUN, CAO XIAN-AN, MIAO XI-YUE, DING XUN-MIN, HOU XIAO-YUAN
Acta Physica Sinica. 1997, 46 (10): 2059 doi: 10.7498/aps.46.2059
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A new method for post-treatment of PS(porous silicon), sulfur passivation by microwave plasma assistance in vacuum,is reported in this paper.Fourier transform infrared spectrum indicated that the treated sample surface is mainly covered by SiSx and SiOy.Compared with the as etched PS,the photoluminescence (PL) intensity of the sample is 3.5 times stronger,and the 4nm blueshift of the PL peak was observed experimentally;furthermore,the intensity decay of the PL peak hasnot been observed after 60d in the atmosphere.Therefore,sulfur passivation is an effective post treatment for enhancing PL intensity and stabilization of PS.

THE OPTICAL PROPERTIES OF STRAINED SUPERLATTICE (ZnS)1/(ZnSe)1(001)

LI KAI-HANG, HUANG MEI-CHUN
Acta Physica Sinica. 1997, 46 (10): 2066 doi: 10.7498/aps.46.2066
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The linear muffin tin orbitals method was adopted to calculate the band structures of the strained- superlattice (ZnS)1/(ZnSe)1(001) grown on the Si substrate.In our calculation the external adjusted potential was used to overcome the problem of too small a band gap in it.On the basis of relatively accurately calculated band structure and wave function for this system,we calculated the imaginary part of dieletric function of the superlattice system.The results showed that the optical properties of (ZnS)1/(ZnSe)1(001) grown on the Si substrate consisted of the optical properties of bulk ZnS and of bulk ZnSe,and they have rather good optical response over a wide range of photon energy;futhermore,the superlattices are direct band gap materials.Thus the superlattices will become the promising materials for optoelectronic device applications.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

STABILITY ENERGY OF GROWTH-UNIT AND MORPHOLOGY OF SPHALERITE CRYSTALLITES

YUAN RU-LIN, SHI ER-WEI, WANG BU-GUO, XIA CHANG-TAI, LI WEN-JUN, ZHONG WEI-ZHOU
Acta Physica Sinica. 1997, 46 (10): 2071 doi: 10.7498/aps.46.2071
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The zinc-based compound crystals, which are composed of zinc-anion coordinate tetrahedrons have two kinds of structure:one is wurtzite and the other is sphalerite.In this article the formation process and the ideal morphology of the sphalerite crystals are studied by calculating the stability energy of the crystal growth unit on the basis of the model of anion coordination polyhedron.The favorable growth unit for the growth of the sphalerite crystal is the tetrahedron.Thus the ideal morphology of sphalerite crystals is tetrahedron.The growth rate of the positive polar plane is different from that of the negative polar plane.It is proved by the calculation that zincoxide crystals are impossible to exist in sphalerite,so are zincsulphide crystals in wurtzite.
GENERAL

LOCAL SYMMETRIES AND CONSTRAINTS IN SELF DUAL GRAVITY

MA YONG-GE, LIANG CAN-BIN
Acta Physica Sinica. 1997, 46 (10): 1873 doi: 10.7498/aps.46.1873
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In Ashtekar's formalism, the phase space of general relativity is imbedded into the phase space of complex SU(2) Yang-Mills theory. In this paper, the approach of analyzing local symmetries and constraints in ordinary feild theories is generalized to the complex field theory, the phase space of the Ashtekar formalism is constructed from the configuration space of the self dual Palatini formalism, and the relationship hetween local symmetries of the configuration space and constraints on the phase space is then discussed.

DIRECT TRANSPORTABLE MODEL OF BROWNIAN MOTOR

ZHAN YONG, BAO JING-DONG, ZHUO YI-ZHONG, WU XI-ZHEN
Acta Physica Sinica. 1997, 46 (10): 1880 doi: 10.7498/aps.46.1880
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A system which uses the non equilibrium fluctuating energy to do work is considered as a result of Brownian motor derived by both internal and external noises. The corresponding diffusion model including damping force and double noise sources is proposed. Through the analytical calculation and numerical simulation, the mechanism of the directed motion of the Brownian motor driven by multiplicative noise and the effect of damping force on the steady current in the one dimensional inertia ratchet potential are accordingly expounded and analyzed. As a application, the experimental phenomenon of the stepping motion of the single motor protein is explained.
ATOMIC AND MOLECULAR PHYSICS

INFLUENCE OF ENVIRONMENTAL RADIATION ON LIFETIMES OF STARK STATES IN HIGHLY EXCITED ATOM

FANG DA-WEI, XIE WEI-JUN, ZHANG SEN
Acta Physica Sinica. 1997, 46 (10): 1888 doi: 10.7498/aps.46.1888
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The populations of n=17,m=0 Stark states of sodium atom in static electric fields have been obtained by two step excitation using tunable lasers. The lifetimes of some selected Stark states and the influences of blackbody radiation on the lifetimes were measured by using delayed electric field ionization. The measured data were compared with the calculated values. The experimental and theoretical results exhibit following behaviours: The total rates of stimulated emission and absorption transitions induced by environmental radiations are of the same order of magnitude in comparison to those of spontaneous transition for the observed n=17 Stark manifold states at room temperature. And this effect is more remarkable for longer lived states. It, along with the effect of the Stark mixing of l sublevels, will reduce the differences among lifetimes of Stark states in a manifold.

CALCULATIONS OF THE SURFACE AND DIFFUSION BARRIERS FOR OXYGEN PENETRATION ON METALS AND THEIR OXIDES

LONG DE-SHUN, WANG YAN-SEN, FANG DU-FEI, TANG JIA-YONG
Acta Physica Sinica. 1997, 46 (10): 1894 doi: 10.7498/aps.46.1894
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Using a simpler calculation scheme, we have investigated the surface penetration barriers and bulk diffusion barriers for oxygen in the simple metals Al,Be,Ca,Mg,Zn and their oxides. The results show that the values of the barriers depend on the crystal structure of the material and on the ability of the lattice to relax during the incorporation process. By comparing the theoretical values of the barriers with the experimental ones, we found that the agreement is basically good.

STRUCTURE AND OSCILLATOR STRENGTH DENSITIES NEAR LⅡ,Ⅲ EDGES OF ARGON

FENG REN-FEI, WU SHU-LAN, LIU YING-HUI, JI QING, XU KE-ZUN
Acta Physica Sinica. 1997, 46 (10): 1901 doi: 10.7498/aps.46.1901
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The high resolution fast electron energy loss spectrum for inner shell 2p electron excitation and ionization of argon has been measured in present work at an electron impact energy of 2500eV and a mean scattering angle of 0°. The ionization limits and effective quantum numbers have been- deduced.- The oscillator strength densities for discrete transitions and two ionization continua were- also- determined.

A LOCAL MODE APPROACH TO MOLECULAR VIBRATION ROTATION SPECTROSCOPY OF LOCAL MODE VIBRATIONAL STATES

WANG XIAO-GANG, ZHU QING-SHI
Acta Physica Sinica. 1997, 46 (10): 1906 doi: 10.7498/aps.46.1906
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We have developed a method to evaluate the effective vibration rotation parameter using the wavefunction from the local mode model, on the basis of the wavefunction equivalence of the two models describing the stretching overtone——the NMDD normal mode model and HCAO local mode model. By using this approach, an improved “α-relation” is derived, which exists among the effective vibration rotation parameters of local mode vibrational state at the local mode limit.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

ANALYSES OF BEAM-WAVE INTERACTION IN A DIELECTRIC LINED SLOW-WAVE WAVEGUIDE WITH A PLASMA COLUMN

WU JIAN-QIANG, LIU SHENG-GANG
Acta Physica Sinica. 1997, 46 (10): 1946 doi: 10.7498/aps.46.1946
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A new type of slow-wave system (SWS) for the beam-wave interaction——putting a plasma column into a dielectric-partially-filled waveguide, is presented. By use of the linear self-consistent field theory, the interaction of a relativistic electron beam with the wave in the SWS is analysed. Determinative dispersion equations are derived for a thin annular relativistic electron beam propagating through the SWS surrounding and existing inside the plasma column, respectively. These dispersion equations are directly solved numerically, and the cut-off frequency, the operation frequency and the growth rate of the waves are obtained. Finally, the effects of the parameters of the plasma column on them are discussed.
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