Chin. Phys. B
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Chin. Phys. B  
  Chin. Phys. B--1993, Vol.2, No.8
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GENERAL

THE SECOND-ORDER APPROXIMATION OF THRESHOLD VALUE OF CHAOS

SU JING-HUI
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 561-568 doi: 10.1088/1004-423X/2/8/001
Full Text: [PDF 173 KB] (Downloads:305)
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For the Melnikov theory of chaos, the second-order approximation is given. Applying the result to the dynamics system with quadratic nonlinear term, it is shown that the threshold of chaos depends on initial condition and can be greater than that of the Melnikov method. The first order variational equations of some nonlinear dynamical systems are all the second-order ordinary differential equations with hyperbolic cosine function, its solution is given.
ATOMIC AND MOLECULAR PHYSICS

INTENSE LASER-INDUCED AUTOIONIZATION OF A “Λ” TYPE ATOM

LI GAO-XIANG, PENG JIN-SHENG
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 569-576 doi: 10.1088/1004-423X/2/8/002
Full Text: [PDF 199 KB] (Downloads:314)
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In this paper, we investigate the intense laser-induced autoionization about a "Λ" type atom by taking into account the second-order ionization processes. The effects of the second-order ionization processes and the second discrete state of the atom on the photoelectron spectrum are discussed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

POSITRON ANNIHILATION WITH VACANCIES IN THIN SURFACE LAYER OF As HEAVILY DOPED Si

LU ZHI-HENG, WANG DA-CHUN, G.K?gel
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 577-582 doi: 10.1088/1004-423X/2/8/003
Full Text: [PDF 170 KB] (Downloads:315)
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The lifetime spectroscopy of slow positron accelerated with linear accelerator and pulse punch system was first used to analyze the vacancies in the thin surface layer of silicon heavily doped with arsenic. The results demonstrated that no mono-vacancy was detected to support the arsenic-vacancy complex models for explaining the electrical deactivation mechanism of arsenic-heavily-doped silicon.

THERMAL STABILITY AND GRAIN GROWTH OF NANOCRYSTALLINE METAL SILVER

ZHANG HONG-FEI, WU XI-JUN
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 583-590 doi: 10.1088/1004-423X/2/8/004
Full Text: [PDF 217 KB] (Downloads:494)
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The nanocrystalline metal silver (n-Ag) with average grain size of 10 nm was synthesized by using an inert gas evaporation and in situ compacting technique. The thermal stability of grain size and grain growth caused by isothermally annealing heat treatment, as well as the thermal behavior during grain growth, have been studied. The results indicated that the thermal stability temperature of grain size is about 200℃. The grain growth depends upon the annealing temperature and exhibits threedifferent stages, i.e., slow, fast, and rapid growth stages, corresponding to the temperature ranges from 200℃ to 300℃, from 300℃ to 400℃ and above 400℃, respectively. An exothermal peak and an endothermal peak occur on the differential scanning calorimetriy (DSC) curve of n-Ag. The exothermal peak and the endothermal peak appear in the temperature range from 200℃ to 400℃, and from 400℃ to 660℃, respectively. The enthalpies calculated from the above two peaks depend on the compacting pressure. Further analyses indicated that the grain growth of n-Ag is related to the release of the surface energy of grains and the interracial energy, as well as the strain energy stored in the bulk samples induced by compacting process.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

STRUCTURE AND PROPERTIES OF THE La-DOPED Bi-2201 SYSTEM

MAO ZHI-QIANG, YANG LI, FAN CHENG-GAO, WANG NAN-LIN, YAO ZHEN, WANG YU, JI MING-RONG, ZHANG YU-HENG
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 591-603 doi: 10.1088/1004-423X/2/8/005
Full Text: [PDF 421 KB] (Downloads:435)
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In this article, the influence of La substitution for Sr on structure and physi-cal properties of the 2201 phase is studied. First, the crystal microstructure of the Bi2.1Sr1.9-xLaxCuOy (0≤x≤1.0) is characterized by means of X-ray diffraction and electron diffraction analyses, it is discovered that in the La-doped 2201 system with increasing La content the 2201 phase undergoes tetragnoal-orthorhombic-monoclinic structural transition. With this phase transition, the modulation vector of the 2201 phase transforms from incommensurate to commensurate, and the period of the mod- ulation wave decreases. Secondly, the superconductivity of this system is analyzed systematically. The results of the resistivity measurement show that the appropriate amount of La doping can raise the superconducting transition temperature (Tc) of the 2201 phase, with x=0.2, Tc reaches as high as 25K. However the excessive doping of La (x≥0.3) leads the 2201 phase to transit from metal to insulator and the su-perconductivity disappears. The measurement of thermoelectric power (TEP) of this system shows that with increasing La content the TEP value also increases gradu-ally. But the interesting point is that the transition from positive to negative in TEP occurs for x=0.2 sample. In addition, the electronic structure and oxygen content of this system are also studied. Based on these, we analyze the relation between the microstructure, electronic structure of the La-doped 2201 phase and its superconduc-tivity, indicating that the type of element substitution with higher valence, together with the microstructural distortion induced by the substitution affects the electronic states of Cu 3d seriously, that is, changes the degree of coulomb correlation of Cu 3d electrons, thus resulting in the transition of the type of carrier of this system and the decrease of hole carrier concentration, as well as the corresponding variation of the superconductivity of La-doped 2201 phase.

57Fe M?SSBAUER STUDY ON (NdDy)TiFe11Ny COMPOUNDS

CAO LEI, KONG LIN-SHU, SHEN BAO-GEN, ZHAO JIAN-CAO, GONG HUA-YANG, CHEN YI-LONG
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 604-609 doi: 10.1088/1004-423X/2/8/006
Full Text: [PDF 171 KB] (Downloads:279)
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57Fe M?ssbauer spectra have been obtained at room temperature for (NdDy)TiFe11, and at 11 K and room temperature for the corresponding nitrides (NdDy)TiFe11Ny. The magnetic behaviors of Fe atoms at different sites have been studied. We have found a larger increase of the hyperfine fields upon nitrogenation due to the higher nitrogen content in these compounds and got a bigger enhancement of the isomer shift in 8j site because of the nearest nitrogen environment.

AN INVESTIGATION FOR THE Cd2+-VACANCIES IN RbCdF3 and CsCdF3 CRYSTALS DOPED WITH Fe3+ IMPURITIES

YU WAN-LUN
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 610-618 doi: 10.1088/1004-423X/2/8/007
Full Text: [PDF 251 KB] (Downloads:311)
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This paper presents high-order perturbation calculations for the zero-field splitting parameters D, F, and a of Fe3+-VCd pairs in RbCdF3 and CsCdF3 crystals doped with Fe3+ impurities. In comparison with experimental data, the present results are better than those obtained in previous work by using the phenomenological su-perposition model of spin-Hamiltonian. Moreover, the crystal fields arising from the Cd2+-vacancy and their induced crystal lattice distortion are analysed and calculated. It is found that the contribution from the Cd2+-vacancies cannot be ignored. Mena-while, we obtain that a ligand F- along the [001]-axis moves towards the central Fe3+ ion by Δ= 0.0020nm in RbCdF3 and 0.0028nm in CsCdF3. These results are quite different from Δ = 0.0104nm and Δ = 0.0112nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy.

FRANZ-KELDYSH OSCILLATION FROM THE SPACE CHARGE REGION OF MBE GaAs FILMS

PAN SHI-HONG, WANG ZHONG-HE, LIU YI, ZHANG CUN-ZHOU, ZHOU XIAO-CHUAN, JIANG JIAN, XU GUI-CHANG
Acta Phys. Sin. (Overseas Edition), 1993, 2 (8): 619-629 doi: 10.1088/1004-423X/2/8/008
Full Text: [PDF 282 KB] (Downloads:326)
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We have investigated doped MBE GaAs films using photoreflectance (PR) spec-troscopy. Special spectral structures have been observed in the vicinity of the funda-mental band gap, which are quite different from the Franz-Keldysh oscillation (FKO) from uniform electric fields under flatband modulations. Numerical analysis has been performed for FKO from electric fields in the space charge region under non-flatband modulations. Some typical FKO line shapes are illustrated. For moderately doped samples the calculated line shapes are basically consistent with experiments. The surface electric field and the Fermi level pinning have also been deduced from exper-iments.
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