中国物理B

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LAMB WAVE MODES IN A TWO-LAYERED SOLID MEDIUM WITH A WEAK INTERFACE

王耀俊, 宁伟, 欧贤华

1994 (8): 561-566. doi: 10.1088/1004-423X/3/8/001

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Using the "spring" model for a weak interface between two solids, we derive the charac-teristic equation for the Lamb waves in a two-layered solid composite and make numerical computations for dispersion curves in an aluminum/copper structure with a rigid or slip interface. The influence of the shear stiffness of the interface on the low order Lamb wave modes is considered.

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DISSOLUTION OF IRON TO COPPER IN Fe₆₀Cu₄₀ ALLOY BY MECHANICAL ALLOYING AND SUBSEQUENT DECOMPOSITION

杨元政, 马学鸣, 王根苗, 董远达, 庄育智

1994 (8): 567-572. doi: 10.1088/1004-423X/3/8/002

摘要 ( 1265 )

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A metastable alloy with composition Fe₆₀Cu₄₀ can be prepared in single phase of a fcc structure by mechanical alloying, although Fe-Cu system is virtually immiscible in its equilibrium state at ambient temperature. The M?ssbauer spectra of this supersaturated solid solution could be fitted by two subspectra whose hyperfine magnetic fields are 200 kOe and 250kOe. In this metastable alloy, the iron atoms at the interface are easy to form clusters characterized as α-Fe at a temperature below 250℃, whereas the iron atoms in the body will cluster together at a higher temperature above 350℃ and behave as γ-Fe, and then transform to ferromagnetic bcc iron occurs.

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ANDERSON TRANSITION ZONE IN THE SOUKOULIS-ECONOMOU MODEL OF ONE-DIMENSIONAL INCOMMENSURATE SYSTEMS

杨富民, 孙金祚

1994 (8): 573-582. doi: 10.1088/1004-423X/3/8/003

摘要 ( 1199 )

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Using numerical calculation method, we have studied the Anderson transition in the Soukoulis-Economou model of one-dimensional incommensurate systems. Our results in-dicate that the Anderson transition in this model should take place gradually, i.e., the transition from the extended state to the localized state should pass through a zone in which the intermediate state is located. We call it the Anderson transition zone of the Soukoulis-Economou model. This new conclusion differs from the traditional concept, which holds that the Anderson transition of the Soukoulis-Economou model occurs abruptly at the mobility edges of this model.

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SUPERCONDUCTING TRANSITION TEMPERATURES AND NORMAL-STATE ELECTRICAL RESISTIVITIES OF Tm_1-xPr_xBa₂Cu₃O_7-δ

曹效文

1994 (8): 583-588. doi: 10.1088/1004-423X/3/8/004

摘要 ( 1108 )

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Superconducting transition temperature T_c and normal-state electrical resistivities ρ of the Tm_1-xPr_xBa₂Cu₃O_7-δ system have been measured. The results indicate that T_c remains constant for x = 0 to 0.08 before it drops steadily with higher x. Following the Abrikosov-Gor'kov model, a total suppression of superconductivity occurs at a critical Pr concentration x_cr≈0.56. It is found for the first time, as far as we know, that the logarithmic resistivity at 270 K increases linearly with increasing x, yielding ρ= ρ₀e^ax. Judging from the relation between dρ/dT and x, a metal to insulator transition occurs just beyond x_cr.

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STUDY OF HALOGEN DOPING IN POLYCRYSTALLINE YBa₂Cu₃O_7-δ

庄瑞舫, 谢辉, 吉和林, 金新, 覃孟军, 徐小农, 姚希贤

1994 (8): 589-594. doi: 10.1088/1004-423X/3/8/005

摘要 ( 1390 )

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This paper presents systematically the doping effects of halogens in YBa₂Cu₃O_7-δ polycrystalline samples, with a series of concentrations of fluorine, chlorine, bromine or iodine. All samples were prepared by chemical method of citrate pyrolysis, which makes the halogen concentration in the samples more uniform. Samples doped with F have T_c as high as 94.5K, Cl, Br and I dopings also raise T_c to a certain extent. In addition, the influence of halogen doping on critical current density, morphology, constitution and so forth is discussed.

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STUDY OF PHOTON-TRAPPING PHENOMENON IN POROUS SILICON LAYER

陈良尧, 侯晓远, 黄大鸣, 张甫龙, 冯星伟, 杨敏, 苏毅, 钱佑华, 王迅

1994 (8): 595-607. doi: 10.1088/1004-423X/3/8/006

摘要 ( 1567 )

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Porous silicon samples were prepared for optical studies by using the photoluminescence (PL), Raman scattering (RS), as well as the absolute reflectance and ellipsometry methods. Results show that the porous Si has low optic constants, and can trap the visible photons of more than 95%, but give no evidence of a strong interband transition existing in the vis-ible region. The Bruggeman effective-medium-approximation (EMA) and Lorentz oscillator models were used in data analyses. Calculations show that the layer dispersion effect may result in a red shift of the PL peak. The possible mechanism for the PL and Raman enhance-ment as well as the photon trap phenomenon was discussed, and was attributed mainly to the random multiple micro-reflections in the porous-Si layer having extremely large internal micro-Burfaces.

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THE INFLUENCE OF THE ADMIXING OF DIFFERENT MULTIPLETS ON THE SPIN MAGNETIC MOMENT AND FARADAY EFFECT OF HARE EARTH IONS IN GARNETS

张国营, 徐游, 杨杰慧

1994 (8): 608-616. doi: 10.1088/1004-423X/3/8/007

摘要 ( 1071 )

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The influence of the admixing of the excited multiplets of the ground configuration with the ground multiplet on the spin magnetic moment of the crystal- field-and exchange-interaction-split ground state, the Faraday rotation and the magneto-optic coefficient induced by the rare earth ions in rare-earth-substituted garnets Y_3-xR_xFe₅O₁₂ (R=Ce and Pr) has been calculated in this paper. It is found that, in the case of Ce³⁺ ions, the admixing of the 4f¹ ²F_7/2 multiplet with the ²F_5/2 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 140% and the Faraday rotation increase by 180% at 633nm wavelength, and 150% at 1150nm at 294 K. In the case of Pr³⁺ ions, the admixing of the 4f² ³H₅ multiplet with the ³H₄ multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 34% and the Faraday rotation increase by 59% at 294K. The admixing of different multiplets of the Ce³⁺ ions makes the ratio between the magneto-optic coefficients at 50 and 294K increase by 7% at 633nm wavelength and 15% at 1150nm.

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A MBE ON-LINE OPTICAL MODULATION PHOTOREFLECTANCE ANALYSIS SYSTEM

何元金, 董悦梅, 段晓东

1994 (8): 617-622. doi: 10.1088/1004-423X/3/8/008

摘要 ( 1222 )

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An on-line optical modulation photoreflectance (PR) spectroscopy analysis system asso-cinted with the molecular beam epitaxy (MBE) system has been designed and established. This paper reports in detail the optical design, the experimental arrangement, and the adjust-ment of the system. GaAs film samples grown by MBE on Si-substrate have been measured with this on-line system. The results show that the on-line PR spectroscopy can characterize the quality of the as-grown film samples qualitatively and promptly.

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MONTE CARLO STUDIES OF RADIATION DAMAGE INDUCED BY FUSION:DYNAMIC SIMULATION OF SPUTTERING

邵其鋆, 潘正瑛, 霍裕昆

1994 (8): 623-629. doi: 10.1088/1004-423X/3/8/009

摘要 ( 1264 )

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In this paper, the sputtering caused by fusion of ⁴He particles in the first wall materials is investigated by using the dynamic Monte Carlo simulation, which is based on the binary collision approximation. The dependences of sputtering yields on the incident energy and angle, as well as the comparisons of results calculated using the Monte Carlo methed with results from experiments, are discussed. Energy spectrum and angular distributions of sputtered species, the depth of origin of the sputtered particles as well as range distributions of incident ions are given. From a comparison between the related experimental data and the calculated results with static and dynamic simulation it has been found that a better agreement is obtained for dynamic simulation.

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