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Acta Physica Sinica  
  Acta Physica Sinica--1998, 47 (2)   Published: 15 February 1998
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CLASSICAL AREA OF PHENOMENOLOGY

NON-DEGENERATE TWO-PHOTON FLUORESCENCE SPECTRUM FOR TWO-LEVEL ATOM IN SQUEEZED VACUUM

HE LIN-SHENG, FENG XUN-LI, WU SHI-XIONG, ZHANG ZHI-MING, XIA YU-XING
Acta Physica Sinica. 1998, 47 (2): 0219 doi: 10.7498/aps.47.219
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In this paper the master equation is derived for the atomic reduced density operator, by means of projection operator technique, starting from the Liouville equation. The nondegenerate two-photon fluorescence spectrum for an atom with two-levels in a squeezed vacuum with broad band has been studied by means of the above equation. We find that there is a new type of oscillation phenomenon, in which there are both super and lower thresholds. Between the two thresholds the atom will exhibit oscillation and the two-photon fluorescence spectrum exhibits single peak. Outside the region between the two thresholds the oscillation will not happen and the two-photon fluorescence spectrum possesses novel negative peak or peaks. The shapes of the spectra depend strongly on the natural two-photon linewidth. However, the spectra are not phase-sensitive, which is unexpected.

ANALYSIS OF THE NOISE IN VCSEL USING RATE EQUATION

ZHANG YI, HUANG YONG-ZHEN, WU RONG-HAN
Acta Physica Sinica. 1998, 47 (2): 0232 doi: 10.7498/aps.47.232
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The noise characteristics of vertical cavity surface emitting laser (VCSEL) are analysed by using rate equations with a reasonable noise simulating method,and the effect of device parameters (such as spontaneous emission factor,output power,injection current and threshold current) on relative intensity noise,frequency noise and spectral linewidth is calculated under single-mode condition.The results are in agreement with experiments.These results may be helpful for optimising the structure design and determing the factors in the application of VCSEL.

ORIENTED GROWTH OF LiNbO3 THIN FILMS ON AMORPHOUS SUBSTRATES IN A LOW ELECTRIC FIELD

WU ZHUANG-CHUN, HU WEI-SHENG, LIU JUN-MING, WANG MU, LIU ZHI-GUO
Acta Physica Sinica. 1998, 47 (2): 0239 doi: 10.7498/aps.47.239
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Both the strength of an applied biased electrical field and the substrate temperature were found to have significant effect on the oriented growth of LiNbO3 thin films prepared by pulsed laser deposition technique.At a substrate temperature of 600℃ and an applied electrical field of 7V/cm,completely (001) oriented LiNbO3 films were deposited on silica and other amorphous substrates successfully.The physical background of the oriented growth of ferroelectrical films induced by low electric field was analyzed in terms of nucleation and growth theory of ferroelectrics with spontaneous polarization in electrical field and the deposition temperature effect on the intensity of spontaneous polarization of the ferroelectrics.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

THE FLUORESCENCE EMISSION FROM GaAs IN THE LAUE CASE NEAR THE ABSORPTION EDGE

XU ZHANG-CHENG, GUO CHANG-LIN, ZHAO ZONG-YAN, T.FUKAMACHI, R.NEGISHI, M.YOSHIZAWA, T.NAKAJIMA
Acta Physica Sinica. 1998, 47 (2): 0252 doi: 10.7498/aps.47.252
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The Ga K fluorescence X-rays emitted from the incident surface of GaAs perfect crystal were observed around the (200) reflection peak in the Laue case,while tuning the energies of incident X-rays from a synchrotron radiation source between the K absorption edges of the Ga and As atoms.With the change of the energies of incident X-rays,the asymmetry of the fluorescence X-ray curves will change accordingly,the tendency is similar to that in the Bragg case.However,the variation in the Laue case cannot be explained by the moving of the nodal planes of X-ray standing wave (XSW) with respect to (200) diffraction plane of GaAs.In the Laue case,the variation of the amplitudes of XSW with the incident angle is closely related to the phase of the structure factor,whose change will result in the change of the asymmetry of fluorescence curves.Under the assumption that the fluorescence yield is proportional to the electric field intensity at the position where the atoms are located,the formulae for calculating the fluorescence emission in the Laue case for perfect crystals are derived.The agreement of the experimental results with the new formulae is quiet good.

MOLECULAR DYNAMICS STUDY ON THE STRUCTURES OF MOLTEN Rb2ZnCl4

CHENG ZHAO-NIAN, DING HONG, LEI YU
Acta Physica Sinica. 1998, 47 (2): 0260 doi: 10.7498/aps.47.260
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The structures of molten and crystalline states of Rb2ZnCl4 have been simulated by molecular dynamics with the effective potentials which had been applied in the simulations of RbCl and ZnCl2 systems.Six radial distribution functions (RDF) simulated are presented,of which Zn-Cl and Rb-Cl RDFs are in good accordance with the recent EXAFS experimental results.Based on the instantaneous configurations given by the simulations,the local structures in molten and crystalline states have been studied with bond-order parameter method.The results show that the Zn atom and its neighboring Cl atoms form a stable tetrahedral structure,and the Zn/Cl tetrahedral structures in molten Rb2ZnCl4 are stabler than those in molten ZnCl2.The presence of a good quantity of stable (ZnCl4)2- units without apparent network-like structures is the typical characteristics of the molten Rb2ZnCl4.The simulations for crystalline state did not describe the complex coordinations between Rb and Cl atoms in detail,which showed that the two-body effective potentials are not enough to simulate the behaviors of Rb atoms in the crystalline Rb2ZnCl4.

EFFECT OF HIGH-PRESSURE ANNEALING ON MICROSTRUCTURAL TRANSFORMATION OF NANOTUBES

ZHANG MING, HE DUAN-WEI, XU YING-FAN, WANG WEN-KUI, LIANG JI, WEI BING-QING, WU DE-HAI
Acta Physica Sinica. 1998, 47 (2): 0270 doi: 10.7498/aps.47.270
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The microstructural transformations of carbon nanotubes under high-pressure annealing have been studied by high resolution transmission electron microscopy. It is found that under 5.5GPa the microstructure of nanotubes has obviously changed at an annealing temperature of 770℃, while onion-like and ribbon-like structures formed at 950℃. The transformation from carbon nanotubes into quasi-spherical onion occurs in several steps, first the shells of nanotubes collapse, then spheres form and finally onion-like structures appear. The effects of high pressure and annealing temperature on microstructural changes are discussed.

NUMERICAL SIMULATION OF THE GROWTH OF Hg1-xCdxTe CRYSTAL BY THE TELLURIUM SOLVENT METHOD

LIU JIA-LU, ZHANG TING-QING, LUO HONG-WEI, YAN BEI-PING, LANG WEI-HE, ZHANG BAO-FENG
Acta Physica Sinica. 1998, 47 (2): 0275 doi: 10.7498/aps.47.275
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A theoretical model is presented describing the growth of Hg1-xCdxTe crystal by the tellurium solvent method under steady growth conditions. The model uses the one-dimensional time-dependent equations of species diffusion with the moving free boundaries of the solution zone determined via consideration of the phase diagram. Numerical solutions are presented for the growth of Hg0.8Cd0.2Te (x=0.2) crystal by the finite difference method. The iufluence of the temperature profile of the solution zone, the velocity of the travelling heater, the length of the initial solution zone and the temperature of the growth interface on the crystal axial composition of HgCdTe is discussed in detail. The simulation results are in good agreement with the experiment.

DEEP ELECTRON STATES IN n-TYPE Al-DOPED ZnS1-xTex GROWN BY MOLECULAR BEAM EPITAXY

LU LI-WU, ZHANG YAN-HUA, GE WEI-KUN, I.K.SOU, Y.WANG, J.WANG, Z.H.MA, W.S.CHEN, G.K.L.WONG
Acta Physica Sinica. 1998, 47 (2): 0286 doi: 10.7498/aps.47.286
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Capacitance-voltage (C-V), photoluminescence (PL) and deep level transient spectroscopy (DLTS) techniques were used to investigate deep electron states in n-type Al-doped ZnS1-xTex epilayers grown by molecular beam epitaxy (MBE). The integrated intensity of the PL spectra obtained from Al-doped ZnS0.977Te0.023 is lower than that of undoped ZnS0.977Te0.023,indicating that some of Al atoms form nonradiative deep traps. Deep level transient Fourier spectroscopy (DLTFS) spectra of the Al-doped ZnS1-xTex(x=0,0.017,0.04 and 0.046,respectively) epilayers reveal that Al doping leads to the formation of two electron traps at 0.21 and 0.39eV below the conduction band. DLTFS results suggest that in addition to the roles of Te as a component of the alloy as well as isoelectronic centers, Te is also involved in the formation of an electron trap, whose energy level relative to the conduction band decreases as Te concentration increases. Our results show that only a small fraction of Al atoms form nonradiative deep defects, indicating clearly that Al is indeed a very good donor impurity for ZnS1-xTexepilayers in the range of Te concentration studied in this work.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

STABILITY OF THE LARGE BIPOLARONS IN TWO AND THREE DIMENSIONS

REN YU-HANG, CHEN QING-HU, SHA JIAN, JIAO ZHENG-KUAN
Acta Physica Sinica. 1998, 47 (2): 0294 doi: 10.7498/aps.47.294
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The large bipolaron in two and three dimensions is investigated by combining anapproximate wave functions for the relative motion and the modified Lee-Low-Pines variational method. The values of the critical coupling constant αc above which bipolarons may exist and the critical ratio of dielectric constants ηc below which bipolarons may exist are evaluated, which are very close to the recent results obtained within a totally different variational approach. In addition, the stability region of bipolarons in the 1/α,η plane is clearly plotted. It is also found that low dimensional materials are more favorable for the formation of bipolarons.

ELECTRON TUNNELING AND NEGATIVE DIFFERENTIAL RESISTANCE OF MIM LIGHT-EMISSION TUNNEL JUNCTION

YU JIAN-HUA, SUN CHENG-XIU, WANG MAO-XIANG, ZHANG YOU-WEN, WEI TONG-LI
Acta Physica Sinica. 1998, 47 (2): 0300 doi: 10.7498/aps.47.300
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We have observed that the apparent negative differential resistance(NDR) comes out in I-V characteristic curves of metal-insulator-metal(MIM) thin film tunnel junction when light-emission from this structure occurs in the experiments.The mechanism of this NDR is that the surface plasmon polariton(SPP),which plays a role of intermediate in the process of light-emission,creates the impeding effect upon tunneling electrons.We have also built the circuit simulation of electron-transfer, computed the numerical solution of I-V characteristic curve,and revealed the key action of SPP on the NDR in I-V characteristic curve and the light-emission from MIM tunnel junction.

NONLINEAR OPTICAL RESPONSE OF EPITAXIAL YBa2Cu3O7-δ FILMS

XU KE-XI, ZHOU SHI-PING, BAO JIA-SHAN
Acta Physica Sinica. 1998, 47 (2): 0307 doi: 10.7498/aps.47.307
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Experiments showed that the non-equiliubrium optical response of epitaxial YBa2Cu3O7-δ films below Tc existed with the illumination of He-Ne laser (λ=0.63μm). We have also found that near the transition region, where dR/dT is vanishing, the optical response becomes a strong nonlinear functions of current. A model was presented to explain the mechanism of the nonlinear behavior based on the interactions between photoexcited quasiparticles and the vortex in high Tc superconductor. We believe that the mechanism of the dissipation induced by light illumination in transition region may be correlated with the mechanism of “irreversibility line” or that of “broaden resistive transition” in magnetic fields.

STRUCTURAL CHARACTERIZATION AND INTRINSIC MAGNETIC PROPERTIES OF THE R3 (Fe,Mo)29 NITRIDES

PAN HONG-GE, WANG XIN-HUA, HAN XIU-FENG, YANG FU-MING, CHEN CHANG-PIN
Acta Physica Sinica. 1998, 47 (2): 0316 doi: 10.7498/aps.47.316
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The structural characterization and intrinsic magnetic properties of the R3(Fe,Mo)29(R=Ce,Nd, Sm, Gd, Tb,Dy and Y) nitrides have been investigated in great detail, including the lattice parameters, Curie temperature TC, saturation magnetization σs and anisotropy field Ba.

STRUCTURAL AND MAGNETIC PROPERTIES OF Pt1-xCux/Co MULTILAYERS

MA PING-PING, ZHENG WU, WANG AI-LING, CUI LI-YA, WANG YIN-JUN, HAN BAO-SHAN, CHEN JIN-CHANG
Acta Physica Sinica. 1998, 47 (2): 0325 doi: 10.7498/aps.47.325
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The structural and magnetic properties of Pt1-xCux/Co multilayers have been investigated. Increasing the concentration of Cu in the Pt spacer layers results in monotonic decrease of the anisotropy and remanence, in a range of x from 0.04—0.30 except in a special range of 0.10—0.15. The reduction of these parameters is related to the growth of random anisotropy because a random distribution of Cu atoms in the Pt spacer layers causes a local distortion of crystal symmetry of Pt. In the special range, an order CuPt phase may appear. In such a case cobalt atoms are affected by a symmetric crystal field like that produced by Pt. These may be the possible explanation of the measured parameters after the doping of Cu in the Pt spacerlayers.

PARALLEL MODEL FOR PHOTOSTIMULATED LUMINESCENCE

ZHAO HUI, WANG YONG-SHENG, XU ZHENG, HOU YAN-BING, XU XU-RONG
Acta Physica Sinica. 1998, 47 (2): 0333 doi: 10.7498/aps.47.333
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In this paper, we analyse two kinds of theoretical models. Based on the study of electron transfer process in photostimulated luminescence, a new model, parallel model, is proposed. In terms of this model, the general expression of photostimulated luminescence process is gained. A kind of photostimulated luminescence material, BaFCl:Eu2+, is fired and a series of spectra are measured. To test this model we compared the theoretical and experimental results in terms of decay process, as well as the difference between two kinds of color centers and the relationship between irradiation dose and luminescent intensity.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

STUDY ON HIGH-TEMPERATURE OXIDIZATION OF LOOSELY-ENTANGLED CARBON NANOTUBES PREPARED BY ARC-DISCHARGE

CHANG BAO-HE, ZHANG HAO, ZHOU WEI-YA, QIAN LU-XI, PAN ZHENG-WEI, MAO JIAN-MIN, LI WEN-ZHI
Acta Physica Sinica. 1998, 47 (2): 0340 doi: 10.7498/aps.47.340
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A large quantity of loosely-entangled carbon nanotubes was prepared by arc-discharge method. Samples containing the nanotubes were oxidized at high temperatures. The tubes can remain after a relatively long time(over 1h) and high-temperature (of 850℃) oxidization. The amounts of the defect and other structure imperfects might be substantially minimized in the loosely-entangled nanotubes, so the stability of the tubes was greatly improved and the nanotube could have much more opportunities to survive during oxidization. This is consistent with Raman scattering results.

GROWTH OF LARGER SIZE C60 AND C70 SINGLE CRYSTALS BY NUCLEATION CONTROL

ZHOU WEI-YA, CHANG BAO-HE, QIAN LU-XI
Acta Physica Sinica. 1998, 47 (2): 0346 doi: 10.7498/aps.47.346
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Larger size C60 and C70 single crystals up to 6mm and 5mm in length, respectively, have been grown by nucleation control, employing an improved double-temperature-gradient furnace. The morphology and the crystal structure of these large crystals were investigated.
GENERAL

DIRAC PARTICLE RADIATION FROM EINSTEIN-MAXWELL-DILATON BLACK PLANE

CAO JIANG-LING, PENG FANG-ZHI
Acta Physica Sinica. 1998, 47 (2): 0177 doi: 10.7498/aps.47.177
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Dirac equation near Einstein-Maxwell-Dilaton black plane's event horizon is analysed and discussed.Under tortoise coordinate translation,it can be verified that there exists thermal radiation of dirac particles from the event horizon.

A NEW METHOD FOR RAPID SOLIDIFICATION QUENCHING BY RAPID DECOMPRESSION

HE DUAN-WEI, ZHANG FU-XIANG, LIU RI-PING, ZHANG MING, XU YING-FAN, WANG WEN-KUI
Acta Physica Sinica. 1998, 47 (2): 0183 doi: 10.7498/aps.47.183
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A rapid drop of pressure applied to a melt whose crystallization point is a decreasing function of the pressure may,if the temperature,the initial pressure and the final pressure are appropriately chosen,be equivalent to a rapid thermal quenching.In particular,it may lead to the formation of metastable crystalline or glassy-phase bulk materials.The method might be useful to simulate adiabatic decompressions subsequent to shocks,such as meteorite impacts.The relation between the corresponding cooling rate(Vc) obtained by rapid decompression and the rate of pressure release(Vp) is first given by Vc=KVp,where K is the drop rate of melting point with pressure.This method is evaluated by using Al-Ge system.Our experimental results indicate that quenching with rapid decompression is an effective method for generating corresponding high cooling rate of more than 105K·s-1.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

THE DISCUSSION ON MOMENTUM CONSERVATION OF GLR EQUATIONS

HE BO, ZHU WEI, XU ZAI-XIN
Acta Physica Sinica. 1998, 47 (2): 0189 doi: 10.7498/aps.47.189
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The GLR equations are the basic equations describing the phenomena in the small x region.Especially it is important to use them for analysing the deep-inelastic lepton-proton scattering and EMC effect.But GLR equations have the defect that they violate the law of conservation of momentum.We discuss this problem and point out the defect in analysing the experiment.
ATOMIC AND MOLECULAR PHYSICS

THEORETICAL DESCRIPTION OF HARMONICS GENERATION FOR TWO-LEVEL ATOMS

QU WEI-XING, HU SU-XING, XU ZHI-ZHAN
Acta Physica Sinica. 1998, 47 (2): 0193 doi: 10.7498/aps.47.193
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The process of harmonic generation for a two-level atom is investigated theoretically.The model of oscillator driven by a nonlinear external force is used to simulate an induced porlarization of the atom,and the characteristics in harmonic spectrum of the atom are analyzed for a weak and a super-intense laser pulses.

THEORETICAL TREATMENT OF RADIATION TRAPPING OF ATOMIC FLUORESCENCE IN V-E ENERGY TRANSFER

WANG CHU-JI, WANG JIAN, MA XING-XIAO
Acta Physica Sinica. 1998, 47 (2): 0198 doi: 10.7498/aps.47.198
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A differential-integral equation system of Holstein type is used to describe the kinetic process in V-E energy transfer between molecules and atoms with radiation trapping.A reduced solution of a finite series has been presented,which allows to describe the whole temporal behavior of fluorescence.The further derivative is an analytical expression of the fluorescence decay rate as a function of rate constants and the maximum eigenvalue of the integral operator appearing in the rate equations.This will be especially useful and convenient for experimental determinations.Results are schematically illustrated and mutually compared by means of numerical calculations.

DETERMINATION OF THE ENERGY GAP OF C60 MOLECULE USING THIRD-ORDER DERIVATIVE ABSORPTION SPECTROSCOPY

ZHAO MING-SHAN, DAI ZUO-XIAO, LI YI, LI GUO-HUA, BU YU-XIANG, YU ZHANG-YU
Acta Physica Sinica. 1998, 47 (2): 0208 doi: 10.7498/aps.47.208
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More detailed absorption transitions of C60 in the visible region are observed from the third-order derivative absorption spectra.The spectra are fitted with Lorentzian line shapes,and the transition energies are determined.The assignment of the transitions in visible region is discussed,some vibronic modes are given,and finally the energy gap of C60 molecule is determined.

OPTICAL ABSORPTION STUDY OF EMBEDDED InP CLUSTER

ZHAO ZI-QIANG, WEI LUN-CUN, LU XI-TING
Acta Physica Sinica. 1998, 47 (2): 0214 doi: 10.7498/aps.47.214
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By using co-evaporating semiconductor and insulator media,InP∶CaF2 films were prepared.Inp was embedded in CaF2 in the form of clusters,whose size could be controlled by gas pressure and evaporating electric current.Transmission electron micrographs showed that the structure of InP cluster was polycrystalline.And the cluster size is about 10nm.We studied linear optical absorption of this kind of films.Quantum effect was observed clearly.With decreasing cluster size,the blue shift of the absorption edge was found.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

PROPAGATION PROPERTIES OF A PLASMA WAVEGUIDE IN A FINITE MAGNETIC FIELD

HU BIN-JIE, RUAN CHENG-LI, LIN WEI-GAN
Acta Physica Sinica. 1998, 47 (2): 0245 doi: 10.7498/aps.47.245
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The propagation properties of a plasma waveguide in a lossy material under a finite magnetic field are analyzed,particularly for the variations of their propagation constants with plasma parameters,surrounding material and external magnetic field.The analysis show that the propagation properties of such a magnetized plasma-filled waveguide are easy to be controlled compared with those of plasma waveguide to which no external magnetic field or an infinite external magnetic field is applied.
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