Table of contents

20 June 1996, Volume 5 Issue 6 Previous issue    Next issue

GENERAL

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A PROPOSAL OF QUANTIZATION OF SYSTEMS WITHOUT STANDARD LAGRANGIANS BAO DE-HAI (鲍德海), ZHU ZHONG-YUAN (朱重远) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  401-408.  DOI: 10.1088/1004-423X/5/6/001 Abstract ( 1164 )   PDF (196KB) ( 378 )   For many classical systems which disobey Helmholtz conditions and thus possess no stan-dard Lagrangian formulation on velocity phase space TQ, ordinary quantization procedures cannot be directly applied. By shifting to an enlarged space TTQ and viewing the systems as typically constrained ones, we propose a quantization method which seems to be practicable as illustrated by the examples.

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FURTHER STUDIES ON NONLINEAR DYNAMICS OF ONE DIMENSIONAL CRYSTALLINE BEAM ZHANG WEI (张伟) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  409-422.  DOI: 10.1088/1004-423X/5/6/002 Abstract ( 1073 )   PDF (289KB) ( 449 )   In thls paper the method of multiple scales, theory of normal form and universal unfolding and the Melnikov's method are used to further study local bifurcations, degenerate bifurcations of codimension two and global bifurcations. Some significant results are obtained.

ATOMIC AND MOLECULAR PHYSICS

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EXPERIMENTAL STUDY OF AC ZEEMAN EFFECT IN 87Rb ATOMIC FREQUENCY STANDARD CHU XIN-ZHAO (初鑫钊), LIU SHU-QIN (刘淑琴), DONG TAI-QIAN (董太乾) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  423-430.  DOI: 10.1088/1004-423X/5/6/003 Abstract ( 1255 )   PDF (174KB) ( 400 )   We have proved experimentally that the frequency shift formula of AC Zeeman effect presented by us is correct. In a 87Rb atomic frequency standard we add a new microwave field which causes the frequency shift of O-O transition frequency of 87Rb atomic ground state. This frequency shift as a function of frequency and power of the added microwave field is measured. The experimental results agree with theory.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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MOLECULAR DYNAMICS STUDY OF LIQUID ALUMINIUM BY EMBEDDED-ATOM METHOD CAI JUN (蔡军), YE YI-YING (叶亦英) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  431-437.  DOI: 10.1088/1004-423X/5/6/004 Abstract ( 1228 )   PDF (197KB) ( 416 )   A molecular-dynamics scheme in the embedded-atom method is shown to be the efficient and accurate in studying liquid aluminium system. The ability of the method in studying liquid system is demonstrated by calculating the intent heat, self-diffusion coefficient, pair distribution function of aluminium, and so on. All of the results agree well with experimental results. The background electron density is also calculated using this method, and the result shows that a discontinuous change occurs at melting point for the electron density in the system.

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OPTICAL-PHONON MODES AND ELECTRON-OPTICAL-PHONON INTERACTION IN A COUPLED QUANTUM WELL SHI JUN-JIE (史俊杰) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  438-449.  DOI: 10.1088/1004-423X/5/6/005 Abstract ( 1332 )   PDF (302KB) ( 376 )   By applying the dielectric continuum model, optical-phonon modes of the lattice vibration and a complete interaction Fr$\ddot{\rm o}$hlich-like Harniltonian between an electron and the optical phonons including the interface phonons, the confined LO phonons and the half-space LO phonons are derived for a general coupled quantum well (GCQW) structure of polar crystals. The dispersion curves of the interface modes and the electron-interface-phonon coupling function as functions of coordinate z and wavenumber k are given and discussed for a GCQW. We find that there are eight (not ten) frequency solutions for the interface optical-phonon modes in GCQW and that, in the long-wavelength limit, the longitudinal and transverse modes in the two side materials 1 and 5 are forbidden and two new frequency solutions $\omega$± are obtained instead. Moreover, we also find that the electron-interface-phonon coupling functions are complicated functions of k and that the phonons with long wavelengths are important and the higher-frequency modes are more important than the lower-frequency modes for the electron-phonon interaction.

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EFFECT OF ATOMIC HYDROGEN ON THE ACETYLENE-ADSORBED Si(100)(2×1) SURFACE AT ROOM TEMPERATURE CHEN YAN (陈岩), LIU ZHAO-HUI (刘朝辉), ZHANG QING-ZHE (张青哲), FENG KE-AN (冯克安), LIN ZHANG-DA (林彰达) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  450-455.  DOI: 10.1088/1004-423X/5/6/006 Abstract ( 1088 )   PDF (165KB) ( 352 )   High resolution electron energy loss spectroscopy, low energy electron diffraction and quadrupole maas spectrometer (QMS) have been employed to study the effect of atomic hydrogen on the acetylene-saturated pre-adsorbed Si(100)(2×1) surface and the surface phase transition at room temperature. It is evident that the atomic hydrogen has a strong effect on the adsorbed C2H2 and the underlying surface structure of Si. The experimental results show that CH and CH2 radicals co-exist on the Si surface after the dosing of atomic hydrogen; meanwhile, the surface structure changes from Si(100)(2×1) to a dominant of (1×1). These results indicate that the atomic hydrogen can open C=C double bonds and change them into C-C single bonds, transfer the adsorbed C2H2 to C2Hx(x = 3,4) and break the underlying Si-Si dimer, but it cannot break the C-C bond intensively. The QMS results show that some C4 species axe formed during the dosing of atomic hydrogen. It may be the result of atomic hydrogen abstraction from C2Hx which leads to carbon catenation between two adjacent C-C directs. The C4 species formed are stable on Si(100) surfaces up to 1100 K, and can be regarded as the potential host of diamond nucleation.

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ELECTRO-LUMINESCENCE AND PHOTO-LUMINESCENCE FROM STRAINED SiGe/Si QUANTUM WELL DONG WEN-FU (董文甫), YANG QIN-QING (杨沁清), LI JIAN (黎建), WANG QI-MING (王启明), CHUI QIAN (崔堑), ZHOU JUN-MING (周钧铭), HUANG QI (黄绮) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  456-462.  DOI: 10.1088/1004-423X/5/6/007 Abstract ( 1132 )   PDF (170KB) ( 434 )   Photo-luminescence and electro-luminescence from step-graded index SiGe/Si quantum well grown by molecular beam epitaxy is reported. The SiGe/Si step-graded index quantum well structure is beneficial to the enhancing of electro-luminescence. The optical and electrical properties of this structure are discussed.

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

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OPTICAL PROPERTIES OF $\delta$-DOPED GaAs AND GaAs/Al0.1Ga0.9As SUPERLATTICES CHENG WEN-CHAO (程文超), XIA JIAN-BAI (夏建白), XU SHI-JIE (徐士杰), ZHENG HOU-ZHI (郑厚植), LUO KE-JIAN (罗克俭), ZHANG PENG-HUA (张鹏华), YANG XIAO-PING (杨小平) Acta Physica Sinica (Overseas Edition), 1996, 5 (6):  463-469.  DOI: 10.1088/1004-423X/5/6/008 Abstract ( 1185 )   PDF (210KB) ( 354 )   Radiative transition in $\delta$-doped GaAs superlattices with and without Al0.1Ga0.9As barriers is investigated by using photoluminescence at low temperatures. The experimental results show that the transition mechanism of $\delta$-doped superlattices is very different from that of ordinary superlattices. Emission intensity of the transition from the electron first excited state to hole states is obviously stronger than that from the electron ground state to hole states due to larger overlap integral between wavefunctions of electrons in the first excited state and hole states. Based on the effective mass theory we have calculated the self-consistent potentials, optical transition matrix elements and photoluminescence spectra for two different samples. By using this model we can explain the main optical characteristics measured. Moreover, after taking into account the bandgap renormalization energy, good agreement between experiment and theory is obtained.