Table of contents

20 November 1998, Volume 7 Issue 11 Previous issue    Next issue

GENERAL

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INFLUENCE OF INTERFACE KINETICS ON THE RELAXATION BEHAVIOR IN SOLUTION SYSTEM FOR CRYSTAL GROWTH UNDER MICROGRAVITY Zhu Zhen-he (朱振和), Ge Pei-wen (葛培文), Xu Zheng-yi (许政一), Huo Chong-ru (霍崇儒) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  801-809.  DOI: 10.1088/1004-423X/7/11/001 Abstract ( 1288 )   PDF (234KB) ( 377 )   The influence of the interface kinetics at the growth face of a crystal and at the surface of material of solute source on the relaxation behavior in a solution system for crystal growth under microgravity is studied. Because the variation of the solution density caused by the solute concentration change can be omitted and only that caused by the temperature change is taken into account, the interface kinetics does not influence the relaxation behaviors of the fluid velocity and the temperature distribution index $S_{\theta}$ (see text). The relaxations of the concentration distribution index $S_{\phi}$ (see text) and dimensionless average growth rate of crystal $\bar{V}_{\rm cg}$ are calculated under the square pulsed fluctuations of the gravity level or the temperature at the growth face of crystal. Introduction of the interface kinetics makes the value of $S_{\phi}$  enlarged and the perturbation peak of the $S_{\phi}$ -$\tau$ curve caused by the gravity level or temperature fluctuation lowered. While the perturbation peak and the valley of the $\bar{V}_{\rm cg}$-$\tau$ curve caused by the negatively and positively pulsed temperature fluctuation, respectively, is lowered and shallowed by the interface kinetics.

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ROOM TEMPERATURE LIGHT-THERMO-DETECTOR MADE OF HIGH-Tc SUPERCONDUCTOR Zhang Peng-xiang (张鹏翔), Li Guo-zhen (李国桢), Zhang Yan (张燕), Wen Xiao-ming (文小明), H. U. Habermeier Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  810-816.  DOI: 10.1088/1004-423X/7/11/002 Abstract ( 1056 )   PDF (216KB) ( 589 )   Based on the anisotropic Seebeck tensor coefficients, a light-thermo-radiation detector made of high-Tc superconductor (YBa2Cu3O7-$\delta$) was fabricated, which can function at room temperature. The induced voltaic signals at various modulation frequencies for radiation from He-Ne laser and from a 500 K black body were measured. The noise ratio for detecting He-Ne laser radiation and the D* for black body were evaluated. Compared with bolometer made of high-Tc superconductor which functions at liquid nitrogen, and with pyroelectric detector, it was found that the advantages of this new device are that the device can work at room temperature with very low noise and very fast response. Although having a lower D* value than that of bolometer for the present device construction, we point out the possibility and the direction for improving the D* value, hence the promising prospect of this kind of device.

ATOMIC AND MOLECULAR PHYSICS

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ENERGETIC ABOVE THRESHOLD IONIZATION SPECTRA OF HELIUM-ATOMS Chen Bao-zhen (陈宝振) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  817-822.  DOI: 10.1088/1004-423X/7/11/003 Abstract ( 1110 )   PDF (200KB) ( 404 )   A new analytic model for the energetic above threshold ionization spectra of He is proposed. The experimental spectra by Mohideen et al. can be accurately described. The serious intensity unconsistency, which appears in the previous calculation, is actually reduced by the present calculation.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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BEHAVIOR OF PLASMA FORMED IN A PAGODA-SHAPED RADIO FREQUENCY PLASMA SOURCE Yao Xin-zi (姚鑫兹), Jiang De-yi (江德仪), Liu Xun-chun (刘训春), Ye Tian-chun (叶甜春) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  823-831.  DOI: 10.1088/1004-423X/7/11/004 Abstract ( 1214 )   PDF (239KB) ( 451 )   A large volume, high density, and pagoda-shaped radio frequency (rf) plasma source has been developed for use in large scale plasma processing. The inductively coupled plasma (ICP) is created by a pagoda-shaped 13.65 MHz antenna to improve the plasma uniformity on substrate. Plasma densities and electron temperatures are measured by using a Langmuir probe and their radial and axial profiles are attained. Electron density of >1×1011 cm-3 on the substrate and uniform to $\leqslant$±1.6% over 16 cm diameter can be produced at argon pressure of 6.65×10-1 Pa and input rf power of 1 kW. ICP etching photoresist in O2 plasma has been tested and the etching uniformity consists with that of the plasma density on the substrate. A large scale etched sample with the uniformity to $\leqslant$±1.1% over 10 cm diameter or to $\leqslant$±2.2% over 13 cm diameter has been obtained.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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STRUCTURAL PHASE TRANSITION IN BISMUTH HIGH-Tc SUPERCONDUCTING MATERIALS UNDER SYMMETRY OF D174h(I4/mmm) Pan Guo-qiang (潘国强) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  832-840.  DOI: 10.1088/1004-423X/7/11/005 Abstract ( 1262 )   PDF (253KB) ( 334 )   By applying the Landau's second-order phase transition theory, the symmetry changes due to the continuous phase transition from the phase of D174h symmetry were studied. The possible low symmetry phases were obtained by minimizing the thermodynamic potential expanded in the order parameters up to fourth order. Some related experimental results were discussed.

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LATTICE DYNAMICS OF WURTZITE SEMICONDUCTORS GaN AND AlN Wei Guang-hong (韦广红), Zi Jian (资剑), Zhang Kai-ming (张开明), Xie Xi-de (谢希德) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  841-850.  DOI: 10.1088/1004-423X/7/11/006 Abstract ( 1490 )   PDF (260KB) ( 1189 )   The lattice dynamics of wurtzite GaN and AlN is studied within the framework of a rigid-ion model. Short-range interactions up to the third nearest neighbors are described by using a valence-force-field potential and the long-range Coulomb interactions between ions are calculated via an Ewald summation. Phonon dispersion curves, density of states and specific heats are presented.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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A DISCRETE VARIATIONAL METHOD STUDY ON THE ELECTRONIC STRUCTURES OF CaMnO3 AND LaMnO3 Yang Zhong-qin (杨中芹), Sun Qiang (孙强), Ye Ling (叶令), Xie Xi-de (谢希德) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  851-863.  DOI: 10.1088/1004-423X/7/11/007 Abstract ( 1492 )   PDF (289KB) ( 642 )   The electronic structures of the perovskite oxides, LaMnO3 and CaMnO3, with various magnetic structures are studied using the first-principles discrete variational (DV) cluster method based on ab initio local-spin-density approximation (LSDA). The ground states of different magnetic phases (including ferromagnetic (FM), A-type antiferromagnetic (A-AFM), and G-type antiferromagnetic (G-AFM)) have been described in this work. The cubic CaMnO3 with observed G-AFM magnetic order is found to have a 0.1 eV calculated gap. Both FM CaMnO3 and LaMnO3 have "half-metallic" character, which is in agreement with other works. LaMnO3 with both A-type and G-type antiferromagnetic order have metallic band structures. Part of Jahn-Teller (JT) distortion (Q2 type) has been taken into consideration for A-AFM LaMnO3. Under Q2 type JT distortion, the occupied and unoccupied states of O 2p and Mn 3d states move farther away from the Fermi energy. It is also found that the distortion can further stabilize the structure. The density of states and the binding energy of the distorted A-AFM LaMnO3 are given in this paper.

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REPLICA SOLUTION TO QUANTUM INFINITE RANGE HEISENBERG MODEL Shang Yu-min (商育民), Yao Kai-lun (姚凯伦) Acta Physica Sinica (Overseas Edition), 1998, 7 (11):  864-869.  DOI: 10.1088/1004-423X/7/11/008 Abstract ( 1176 )   PDF (190KB) ( 379 )   By using replica method and Matsubara imaginary-time functional-integral technique, the quantum infinite range Heisenberg model is solved. The solution shows that the quantum infinite range Heisenberg model also has phase transition.