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Vol. 49, No. 9 (2000)

2000-05-05
GENERAL
OBTAIN HIGH DIMENSIONAL INTEGRABLE MODELS BY MEANS OF MIURA TYPE NONINVERTIBLE T RANSFORMATION
LOU SEN-YUE
2000, 49 (9): 1657-1662. doi: 10.7498/aps.49.1657
Abstract +
Searching for high dimensional integrable models (especially in 3+1 dimensions) is one of the most important problems in nonlinear physics.In this paper,we esta blish a method to find some high dimensional integrable models via some noninver tible deformation relations.A noninvertible deformation relation may not only tr ansform an integrable model to a nonintegrable model,but also deform a nonintegrable model to an integrable model.Concretely,starting from a noninver-tible Miur a type transformation relation and the linear wave equation,we obtain a nontrivi al high dimensional Painleve integrable model.
THE PANCHARATNAM PHASE FOR THE JAYNES-CUMMINGS MODEL WITH TIME-DEPENDENT MODULAT ION
HOU BANG-PIN
2000, 49 (9): 1663-1666. doi: 10.7498/aps.49.1663
Abstract +
Based on the SU(2) group for the Jaynes-Cummings model with time-dependent modul ation,we obtain its pancharatnam phase and analyse the phase changes during the whole process from adiabatically switching on to switching off of the interactio n of the atom with the field.Finally,we discuss the results in the semiclassical approximation.
THE QUOTIENT FUNCTION AND MLLER TRANSFORMATION
ZHANG YONG-ZHAO, ZHANG SHU-YAN
2000, 49 (9): 1667-1669. doi: 10.7498/aps.49.1667
Abstract +
We derive the Lorentz transformation of accelerating system by using the propert ies of quotient function and obtain the famous Mller transformation on its ba sis.
THE EFFECT OF GYROSCOPIC PRECESSION IN SEN SPACETIME
PENG YI, LIANG ZHI-BIN, JING JI-LIANG, HUANG YI-BIN
2000, 49 (9): 1670-1678. doi: 10.7498/aps.49.1670
Abstract +
The effect of gyroscopic precession in Sen spacetime is investigated using Frenet-Serret formalism,and general precession formulas for circular orbits with arbi trary constant angular speed are deduced.The precession angle on the equatiorial plane and along the circular geodesics can be obtained easily from the general formulas.The effect of gyroscopic precession in static dilaton spacetime is also studied as a special case.Comparing these results with those in the Kerr-Newman and Reissner-Nordstrm spacetime respectively,we find that dilaton coupling wi ll decrease the effect of precession.
BOUNDARY CRISIS IN A 2D PIECE-WISE SMOOTH MAP*
MA MING-QUAN, WANG WEN-XIU, HE DA-REN
2000, 49 (9): 1679-1682. doi: 10.7498/aps.49.1679
Abstract +
This paper analytically discusses the characteristics of boundary crisis in a mo del of impact oscillator,and proves that the scaling behavior of the life time after crisis follows the rule τ-ε-γ and γ=ln|β2|ln|β1β2|.Here β1 and β2 are the unstab le and stable eigenvalues,respectively,of a saddle node on the basin boundary of a chaotic attractor.This rule is completely different from that in everywhere-s mooth maps.
STUDY ON THE HOT-CARRIER-DEGRADATION MECHANISM AND HOT-CARRIER-EFFECT IMMUNITY I N ADVANCED GROOVED-GATE PMOSFET
REN HONG-XIA, HAO YUE
2000, 49 (9): 1683-1688. doi: 10.7498/aps.49.1683
Abstract +
In this paper,the hot-carrier mechanism in grooved-gate MOS is analyzed at first .It is found that the hot-carrier effect reaches its highest generate rate under medium gate bias voltage of the three stress areas.Then,the characteristics of hot-carrier-effect in grooved-gate and planar PMOSFET are simulated using advanc ed 2-dimensional device simulator.The results show that the hot-carrier generate d in grooved-gate PMOSFET is far less than in planar PMOSFET,especially for the case of channel length in deep-sub-micron and super deep-sub-micron region.In or der to investigate the other influences of hot-carrier-effect immunity on device characteristics,the drift of gate and drain characteristics induced by differen t interface state is studied for grooved-gate and planar devices.It shows that t he drift induced by same interface state in grooved-gate MOSFET is far larger th an in planar device.This work lays a foundation for the research and design of n ovel very-small-size grooved gate CMOS devices.
ATOMIC AND MOLECULAR PHYSICS
FLUORESCENCE EXCITATION SPECTRUM OF B2Σ+—X2 Σ+ OF AlO RADICAL IN A SUPERSONIC JET
JIN JIN, CHEN YANG, PEI LIN-SEN, HU CHANG-JIN, MA XING-XIAO, CHEN CONG-XIANG
2000, 49 (9): 1689-1691. doi: 10.7498/aps.49.1689
Abstract +
Laser-induced fluorescence excitation spectrum of B2Σ+— X2Σ+ transition of gas-phase AlO radical cooled in a supe rsonic jet has been observed in the range of 430—480nm.AlO was produced by reac ting O2 with Al atoms from a dc discharge-sputtering source.The obser ved vibrational bands were identified as V′-V″=1,2,3 transitions respectively. The vibrational frequencies and anharmonic constants were obtained for both the ground state X2Σ+ and the excited state B2Σ+.Furthermore a rotational analysis of the (1,4) band was made.The abno rmal intensity of the V″=5 transitions is discussed.
THE INTERATOMIC INTERACTION AND PHONON DISPERSIONS IN IRON
LI MI
2000, 49 (9): 1692-1695. doi: 10.7498/aps.49.1692
Abstract +
In the present paper the interatomic interaction in iron is calculated from the cohesive energy by means of the Mbius transform formula.The atomic force const ants are calculated using the calculated potential and then the phonon dispersions.In the calculation it is found that only the two-body potential in the intera ction is insufficient,and the three-body potential also needs to be taken into a ccount.In the later calculation the Slater-Kirkwood type three-body potential is used and the calculated results of the phonon dispersions along three major dir ections [100],[110] and [111] are in good agreement with experiment.
CLASSICAL AREA OF PHENOMENOLOGY
ANALYSIS OF THE PROPAGATING PROPERTIES OF PULSE VOLTAGE AND CURRENT ON DIPOLE AN TENNAS BY EQUIVALENT CIRCUIT METHOD
WANG JUN-HONG
2000, 49 (9): 1696-1701. doi: 10.7498/aps.49.1696
Abstract +
The distributed static capacitance of the dipole antenna was solved by finite di fference method. The influences of the antenna configuration coefficients on the distributed capacitance were analyzed. An equivalent circuit for dipole antenna s, which can be solved in time-domain, was put forward by the distributed static capacitance and the inductance. A corresponding time-domain approach for solvin g this circuit was proposed. By these equivalent circuit and the approach, the v alues of voltage and current at any point of the antenna and at any time can be solved, no matter what pulse source is fed to the antenna. Therefore, the propag ating properties of the pulse voltage and current along the antenna can be analy zed, and the phenomena occurring in the propagating procedure can be explained.
ELECTROMAGNETIC WAVE REFLECTION AND TRANSMISSION OF ANISOTROPIC LAYERED MEDIA BY GENERALIZED PROPAGATION MATRIX METHOD
ZHENG HONG-XING GE, DE-BIAO
2000, 49 (9): 1702-1705. doi: 10.7498/aps.49.1702
Abstract +
The characteristic waves in layered anisotropic medium are discussed on the basi s of propagation matrix concerning the transverse field components.The analytica l expressions for the reflection and transmission coefficients of the waves in a nisotropic layered media are obtained.This formula can be applied to layered uni axial and gyrotropic medium,and anisotropic half space problems as well.
ENTROPY PROPETIES AND SCHRODINGER-CAT STATES OF THE FIELD INTERACTING WITH A Ξ TYPE THREE-LEVEL ATOM
LIU AN-LING, LIU XIANG, FANG MAO-FA
2000, 49 (9): 1706-1713. doi: 10.7498/aps.49.1706
Abstract +
In this paper, we study the entropy properties of the field interacting with a Ξ type three-level atom, derive the calculating formula of the field(atomic)ent ropy, and discuss the influence of the initial atomic state and the one-photon d etuning on the field(atomic)entropy. With the help of Q function of the field(qu asiprobability distribution), the statistical properties of the field states are discussed. It is shown that the field is in the Schrodinger-Cat state at t=12TR when the atom is initially in the middle-level.
ENTROPY PROPERTIES OF THE FIELD OR THE ATOM IN THE INTERACTING SYSTEM OF TWO-MOD E FIELD WITH THE V-TYPE THREE-LEVEL ATOM IN A KERR-LIKE MEDIUM
LAI ZHEN-JIANG, LIU ZI-XIN
2000, 49 (9): 1714-1718. doi: 10.7498/aps.49.1714
Abstract +
Using the method of the systematic state vector we formulate the entropy of the V-type three-level atom interacting with initially uncorrelated two-mode coheren t states of arbitrary detunings in a cavity filled with Kerr-like medium. It is shown by numerical calculation that the behavior of the entropy is strongly affe cted by the Kerr medium. Weak Kerr medium improves the quantum correlation. Stro nger Kerr medium induces strongly periodic fluctuation of the quantum correlatio n between the atom and the fields.
TIME EVOLUTION OF ATOMIC RESPONSE AND LIGHT AMPLIFICATION MECHANISM IN AN OPEN I NVERSIONLESS LASING SYSTEM
TIAN SHU-FEN, BAI CHENG-JIE, FAN XI-JUN, LI JIAN, LIU JIE
2000, 49 (9): 1719-1725. doi: 10.7498/aps.49.1719
Abstract +
We study the law of time evolution of atomic response in an open Λ-type inversi onless lasing system,elucidate the light amplification mechanism without inversi on,and find that the character of the time evolution of atomic response in an open system is obviously different from that in a corresponding closed system. Weconsider that the variation of the oscillation frequency and anharmonic oscillat ion in the process of time evolution originate from the stochastic coherence pro perty of atom oscillators in the system.
SECOND HARMONIC GENERATION IN THE SYSTEM Ge-As-S ADN ANALYSIS OF THE POLING MECH ANISM
ZHAO XIU-JIAN, LIU QI-MING, GAN FU-XI
2000, 49 (9): 1726-1730. doi: 10.7498/aps.49.1726
Abstract +
By the method of Maker fringes,second harmonic generation effect was first obser ved in the electron-beam irradiated Ge-As-S glasses. The poling mechanism was st udied by the method of thermally stimulated depolarization current (TSDC) and th e poled regions was found in the thin surface layer of glasses,which was the sam e as the calculated result in theory.
THEORETICAL AND EXPERIMENTAL INVESTIGATIONS ON SAGNAC INTERFEROMETER BASED ON SI NGLE OPTICAL FIBER GRATING
SHU XUE-WEN, HUANG DE-XIU, DENG GUI-HUA, SHI WEI, JIANG SHAN
2000, 49 (9): 1731-1735. doi: 10.7498/aps.49.1731
Abstract +
A novel Sagnac interferometer employing an optical fiber grating in its loop is presented.The transmission responses of the loops with uniform Bragg gratings an d linearly chirped fiber gratings are calculated. The analytic expressions for the loop with a uniform Bragg grating are given. It is found that the loop of a u niform grating leads to equally spaced band-passes,while that of a chirped fiber grating leads to unequally spaced band-passes. Such Sagnac loops may find appli cations in dense wavelength division multiplexing (DWDM) systems and optical fib er sensing. The multiple band-passes filters with 8 and 16 channels are demonstr ated experimentally. The experiments verify the results of our analysis.
SOLITARY WAVE IN ONE-DIMENSIONAL MONOATOMIC CHAIN UNDER THE CONSIDERATION OF THE SECOND-NEIGHBORS INTERACTION
WANG DENG-LONG, TANG YI, YAN XIAO-HONG
2000, 49 (9): 1736-1740. doi: 10.7498/aps.49.1736
Abstract +
Employing multiple scales method combined with a quasidiscreteness approximation, we investigate the wave motive equation in a one-dimensional homogeneous lattice chain with second-nearest neighbors interaction, and get a new linear dispers ion relation. The result shows that, taking into consideration the second neares t-neighbor interaction and quartic anharmonic interaction simultaneously, the on e-dimensional homogeneous lattice exhibits not only envelope soliton, kink and a ntikink, but also another non-linear elementary excitation in solitary wave form -the breather.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
NONLINEAR LOCALIZED MODES IN A ONE-DIMENSIONAL DIAMOND-STRUCTURE LATTICE
XIA QING-LIN, YAN JIA-REN, ZHOU GUANG-HUI
2000, 49 (9): 1741-1746. doi: 10.7498/aps.49.1741
Abstract +
The nonlinear localized vibrational modes in an anharmonic atomic chain with uniform mass but two alternating force constants between nearest-neighbors are stud ied by means of multiple-scale expansion. This atomic chain models the vibration s of an arrow of atoms in the direction of a diamond-structure lattice or a molecular chain. It is shown that the distribution of the atomic displacements is governed by a perturbed nonlinear Schrdinger equation, and both the statio nary and moving solutions are obtained. The results are somewhat different from that of the diatomic chain with uniform force constants but two alternating mass es. The reason may be that the translational symmetry of diamond-structure latti ce is comparetively lower.
A SEMIEMPIRICAL STUDY OF THE Sb/Si(001) SURFACE
HE YAO, CHE JING-GUANG
2000, 49 (9): 1747-1755. doi: 10.7498/aps.49.1747
Abstract +
The properties of Sb adsorption on the Si(001) substrate have been studied by us ing the semiempirical approach for calculating the surface stress based on the C hadi's model and the Green's function method. It is shown that the Sb atoms form symmetric dimers on the Si(001) surface with the dimer bond length being 0.293n m. No significant relaxations can be found in subsurface layers. The Sb/Si(001)2 ×1 surface is shown to be under tensile stress of 1.0eV/(1×1cell) along the di mer direction and compress stress of-1.1eV(1×1cell) perpendicular to the dimer direction. The main contribution of surface stress of Sb/Si(001) comes from the top three layers.
THE NUCLEATION AND GROWTH OF (100) TEXTURED DIAMOND FILMS IN PRESENCE OF NITROG EN
LI CAN-HUA, WANG GUAN-ZHONG, LIAO YUAN, CHANG CHAO, FANG RONG-CHUAN
2000, 49 (9): 1756-1763. doi: 10.7498/aps.49.1756
Abstract +
We have studied the influence of nitrogen addition in CH4/H2 gas mixtures on the nucleation, morphology and growth rate of polycrystalline diamond films prepared by hot filament chemical vapor deposition (HFCVD). The p resence of nitrogen has little effect on diamond nucleation density, but is bene ficial to enhance the growth rate and to stabilize (100) facets of diamond films . Optical emission spectroscopy was applied to detect the chemical radicals in t he system. It is shown that the additional nitrogen makes the chemical radicals and surface activity of diamond films change tremendously. We believed that nitr ogenous species abstract the atomic hydrogen on the diamond surface and speed up the desorption rate of H, so as to promote the diamond films deposition. Furthe rmore, the selective absorption of nitrogenous species causes chemical roughenin g of the (100) facets, which makes the growth rate of (100) facet higher than th at of other facets and leads to the presence of (100) textured diamond films.
EFFECT OF THE MAGNETIC MIRROR FIELD ON THE ION ENERGY DISTRIBUTIONS IN A RADIO F REQUENCY PLASMA
LIU HONG-XIANG, WEI HE-LIN, LIU ZU-LI, LIU YAN-HONG, WANG JUN-ZHEN
2000, 49 (9): 1764-1768. doi: 10.7498/aps.49.1764
Abstract +
In this article, using the retarding grid energy analyzer, we have measured the ion energy distributions in a low temperature radio fruquency plasma under the condition of different magnetic mirror parameters. At the centre of discharge cell, the ion energy distributions displace in the direction of low energy with the increase of the magnetic density without evident variation in the ion energy distribution width. With the increase of the magnetic mirror ratio, the ion energy distribution displaces in the direction of high energy, and the width of ion energy distribution became wider. So the magnetic mirror parameters have significant effect on the ion energy distributions.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
THE REDUCED MATRICES OF VIBRATIONAL FREQUENCIES IN THE T1uhg JAHN-TELLER SYSTEM
Q.C.QIU, YUAN NAI-RONG, WU HONG-YAN, LI ZHENG
2000, 49 (9): 1769-1777. doi: 10.7498/aps.49.1769
Abstract +
In the studies of the vibronic coupling in C60 molecules,the most imp ortant coupling model is between the T1u electronic states and the hg vibrational modes which is usually called T1uhg Jahn-Teller(JT) stsyem.In the linear T1uhg JT system ,the adiabatic potential energy surface contains a trough only.However,when quad ratic coupling is considered,the potential energy surface will be warped into we lls of either D3d or D5d symmetry.On the assumption that t he vibrational frequencies are isotropic, all the components of hg mo de are identical.Unfortunately,this is not true.The vibrational hg mo de will be split into defferent modes based on the symmetry of wells due to the vibronic coupling.Using group theory and ?pik-Pryce method,all the reduced matr ices of hg vibrational mode are found in this paper.These matrices ar e very useful in studying the anisotropic effects of the vibronic coupling,espec ially in the anion state of the C60 molecules.
THE POLARIZABILITY OF EXCITON AND BIEXCITON IN POLYMER(ANALYTICAL CALCULATION)
ZHAO ER-HAI, SUN XIN, CHEN KE, FU ROU-LI
2000, 49 (9): 1778-1785. doi: 10.7498/aps.49.1778
Abstract +
Since the electroluminescence in polymer comes from the transportation and combination of carriers in the electric field,it is essential to study the polarization property of the excitation in polymer.First we obtain the analytic solutions of exciton and biexciton,then their polarizabilities are calculated using the Green function method.An important result is that we analytically proved that the polarizability of the exciton is positive and that of the biexciton is negative.It follows that the polarization will be reversed when the exciton becomes biexciton.
MONTE CARLO SIMULATION OF ELECTRON TRANSPORT IN 6H-SiC
SHANG YE-CHUN, ZHANG YI-MEN, ZHANG YU-MING
2000, 49 (9): 1786-1791. doi: 10.7498/aps.49.1786
Abstract +
Temperature-and electric field-dependent electron transport in 6H-SiC has been s tudied by single-particle Monte Carlo technique,and the Hall electron mobility i n 6H-SiC has been measured over the temperature range 77K‖c/μ⊥c in 6H-SiC is nearly 5,and the saturation velocity vs is 2×107cm/s.The simulated results are in good agreement with measured data in a wide range of temperature and electric field.
THEORETICAL ANALYSIS OF WAVELENGTH CONVERSION FOR CASCADING SECOND-ORDER NONLINE ARITIES IN SILICA FIBER
LIU XUE-MING, LIU LING, SUN XIAO-HAN, ZHANG MING-DE
2000, 49 (9): 1792-1797. doi: 10.7498/aps.49.1792
Abstract +
A novel wavelength conversion method for wavelength division multiplexing(WDM) n ets by use of cascaded second-order nonlinearities (χ(2)∶χ(2) ) in D-fiber grating after periodically thermal/electric-field poling is p roposed,and is theoretically analyzed for the first time.The coupled mode equati ons of the χ(2)∶χ(2) nonlinearities are derived,and the analytic expressions for the electric-field intensity amplitude of the conversi on light waves and conversion efficiency η are obtained under the small signal condition,which are well consistent with numerical calculations.Both analytic ex pressions and numerical results show that,under the suitabl phase-matching condi tion,η is proportional to the logarithm of the square of pump light power,and the 4th power of the grating length L & second-order nonlinearity d.The calculat ed results also show that the wavelength conversion efficiency η and conversion bandwidth Δλ of over-17dB and 120nm respectively can be reached with this fib er grating.With the increase of L,η increases quickly white Δλ decreases quic kly.The results of simulated calculation and theoretical analysis show that the cascaded χ(2)∶χ(2) process is different from that of qu asi-phases-matched difference-frequency-generation.
THE TRANSPORT MECHANISM IN NANOCRYSTALLINE SILICON FILMS AT LOW TEMPERATURE
WANG TIAN-MIN, XU GANG-YI, HE YU-LIANG, MA ZHI-XUN, ZHENG GUO-ZHEN
2000, 49 (9): 1798-1803. doi: 10.7498/aps.49.1798
Abstract +
In a wide temperature range (500—20 K), we studied the electrical transport mechanism in intrinsic and P-doped nanocrystalline silicon films. We find that the HQD model successfully explains the conductivity at high temperatures (500—200K ), but fails at temperature below 200K. Single activation energy W was found in the low temperature range (100—20K), which is approximately equal to the value of kBT(W~1—3kBT).It is in good agreement with the charac teristics of hopping conduction in amorphous semiconductor, In this paper we mod ified the HQD model. We consider two distinct transport mechanisms, thermal-assi sted tunneling and electrons hopping through the local states near the Fermi lev el exist simultaneously. At high temperature tunneling transport is the main pro cess. At low temperature transport is governed by electron hopping. On this basi s, a complete analytic function of the conductivity is proposed. The function su ccessfully explains the conductivity of intrinsic and P-doped nanocrystalline si licon films in the whole temperature range.
STUDY ON TRANSPORT PROPERTIES OF TWO-DIMENSIONAL ELECTRON GASES IN n-Hg0.80 Mg0.20Te INTERFACE ACCUMULATION LAYER
JIANG CHUN-PING, GUI YONG-SHENG, ZHENG GUO-ZHEN, MA ZHI-XUN, LI BIAO, GUO SHAO-L ING, CHU JUN-HAO
2000, 49 (9): 1804-1808. doi: 10.7498/aps.49.1804
Abstract +
The transport properties in Hg0.80Mg0.20Te molecular beam epitaxy film has been studied in the temperature range from 15 to 250K by vari able magnetic-field Hall measurement.The experimental data have been analyzed us ing a hybrid approach consisting of the mobility spectrum(MS) technique followed by a multicarrier fitting(MCF) procedure.Both Shubnikov de Hass(SdH) Measuremen ts and the hybrid approach show two- and three-dimensional electronic behaviors. Experimental results indicate that the two-dimensional electrons are due to an a ccumulation layer near the Hg1-xMgxTe-CdTe interface or th e Hg1-xMgxTe-vacuum interface.Ionized impurity scattering of the three-dimension electron mobility dominates at low temperature(considerin g the screening effect) while lattice scattering dominates above 100K.The scatte ring mechanism in Hg1-xMgxTe is very similar to that in Hg 1-xCdxTe.
THE MICRO-PHOTOLUMINESCENCE OF A SINGLE V-GROOVE GaAs/AlGaAs QUANTUM WIRE
H.H.TAN, C. JAGADISH, Y.FU, M.WILLANDER, LI ZHI-FENG, LU WEI, LIU XING-QUAN, SHEN XUE-CHU
2000, 49 (9): 1809-1813. doi: 10.7498/aps.49.1809
Abstract +
The micro-photoluminescence(μ-PL) scan has been performed on a single V-groove GaAs/AlGaAs quantum wire in the direction perpendicular to the wire.The variatio n of μ-PL spectra from various quantum structures with different spatial positi ons has been observed.In the region of quantum wire (QWR) the PL spectra contain the peaks from QWR,necking quantum well (NQWL) and vertical quantum well (VQWL) ,while in the area about 1μm and farther away from the QWR the PL spectra show the peaks from side-wall quantum well (SQWL) and top quantum well (TQWL).All the scanned PL spectra have been fitted by Gauss line shape.The asymmetric PL peaks of QWR and SQWL were decomposed into two components which were ascribed to the optical transitions between the electron ground state in the conduction band and the heavy hole and the light hole ground states in the valence band.The variati on of PL intensity from luminescent components with the spatial positions direct ly demonstrates the origin of the photoluminescence relating to different quantu m structures,and reflects the carrier transfer from SQWL to QWR,resulting in th e PL quenching of SQWL.
TUNNELING TRANSPORT OF TWO-DIMENSIONAL SPIN-ELECTRONS THROUGH MAGNETIC QUANTUM S TRUCTURES
GUO YONG, GU BING-LIN, YOSHIYUKI KAWAZOE
2000, 49 (9): 1814-1820. doi: 10.7498/aps.49.1814
Abstract +
Spin tunneling transport properties of two-dimensional electrons through magnetic quantum structures are investigated at zero bias and finite bias. The resultsi ndicate that spin-dependent features are not only related with the magnetic conf iguration, the incident electron energy and the wave-vector, but also closely re lated with the applied bias. At zero bias, the magnetic quantum structure compos ed of identical magnetic-barrier and magnetic-well does not show spin-filtering properties, while the magnetic quantum structure composed of unidentical magneti c-barrier and magnetic-well shows distinct spin-filtering properties. Moreover, the applied bias greatly changes electron spin polarization, which makes the for mer structure also showing interesting spin-dependent features under an applied bias.
FOURIER TRANSFORMATION STUDY OF THE FRANZ-KELDYSH OSCILLATION IN SIN+ GaAs STRUCTURES
JIN PENG, PAN SHI-HONG, LIANG JI-BEN
2000, 49 (9): 1821-1828. doi: 10.7498/aps.49.1821
Abstract +
Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectanc e measurements.The FT spectra of a part of the samples,including of the real par t,imaginary part,and mode of the FT,are well consistent with the theoretical lin eshapes.The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH),μl/μh,obtained in the analysis wa s in the range of 0805 to 0816 for different samples.In addition,the built-i n electric field F1,and the modulation field δF=F1-F2 induced by photo-modulation were also obtained in the analysis.However ,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape.In this ca se the mode of the FT spectra still can be used to obtain useful information.
SIMULATION ON LOCAL FLUX CREEP IN NON-IDEAL TYPE-Ⅱ SUPERCONDUCTORS:THE EFFECT O F NON-UNIFORM PINNING POTENTIAL AND SURFACE POTENTIAL
LIU FENG, YAN SHOU-SHENG
2000, 49 (9): 1829-1837. doi: 10.7498/aps.49.1829
Abstract +
Based on the thermally activated model,the flux creep process in the case of non-uniform pinning potential and surface pinning potential in nonideal type Ⅱ sup erconductors is studied through computer simulation.Global and local magnetizati on curves are calculated and the logarithmic time dependence of local magnetic i nduction under a constant external field is examined.The results show that the m otion of the flux is much restrained in the non-uniform case and the flux line i s easy to be captured by the strong pinning center.The surface potential has mar ked effect in preventing the flux from going into and leaving the sample.Compare d with the global behavior,the local magnetization is much more sensitive to the non-uniform pinning potential and the magnetic field sweep rate.
SPONTANEOUS MAGNETIC PHASE TRANSITION AND MAGNETOELASTIC ANOMALIES AT TRANSITION S IN INTERMETALLIC COMPOUNDS RMn2Ge2 (R=La,Pr,Nd,Sm,Gd,Tb, Y)
R.Z.LEVITIN, GUO GUANG-HUA
2000, 49 (9): 1838-1845. doi: 10.7498/aps.49.1838
Abstract +
The temperature dependence of lattice constants a and c of intermetallic compounds RMn2Ge2 (R=La,Pr,Nd,Sm,Gd,Tb and Y)is measured in the t emperature range 10—800K using the X-ray method. The magnetoelastic anomalies o f a(T) and c(T) are found at different spontaneous magnetic phase transitions. I t is shown that the magnetoelastic anomalies are mainly determined by the Mn-sub system. Mn-Mn exchange interactions depend not only on the lattice constant a bu t also on constant c. Low-temperature ferromagnetic-antiferromagnetic transition s are discussed in the framework of Kittle's exchange inversion model.
ELECTRONIC SPIN RESONANCE STUDY OF PEROVSKITE-TYPE MANGANITES
JIANG YONG, LI GUANG, ZENG XIANG-YONG, YANG YING-PING, YUAN SONG-LIU, JIN SI-ZHAO
2000, 49 (9): 1846-1851. doi: 10.7498/aps.49.1846
Abstract +
The electron spin resonance behavior of two typical systems with Mn3+ /Mn4+=2∶1 and 1∶1 within the temperature range T>TC is s tudied experimentally. The results show that there exists a temperature Tmi n(>TC)dividing the magnetic behavior above TC into t wo distinguishable regime. While T>Tmin, The ESR spectrum consists of one symmetrical resonance line. The Lande factor is independent of temperature and close to the value of free electron (~20023), and the linewidth increase s linearly with increasing temperature. Some distortions are observed when the t emperature is lower than Tmin. The line shape becomes unsymmetrical. The g factor become dependent on the temperature and the linewidth increases ano malously with decreasing temperature. These results point out that the complete paramagnetism exits only in the temperature range T>Tmin. When T Cmin,the anomalous paramagnetic behavior may be caused by t he magnetic inhomogeneity. The mechanism of resonance linewidth broadening is di scussed based on an analysis of the linewidth above Tmin, suggesting that the exchange narrowing spin-spin interaction and the spin-lattice interacti on are two possible reasons of linewidth changes in the high temperature regime.
ELECTRIC FIELD INDUCED ANTIFERROELECTRIC TO FERROELECTRIC PHASE TRANSITION OF Pb (Zr,Sn,Ti)O3 CERAMICS AND TAILORING OF PROPERTIES THROUGH COMPOSITION MODIFICATION
LIU PENG, YANG TONG-QING, ZHANG LIANG-YING, YAO XI, XU ZHUO
2000, 49 (9): 1852-1858. doi: 10.7498/aps.49.1852
Abstract +
In order to obtain a new kind of antiferroelectric (AFEt) ceramics wi th lower AFEt-Ferroelectric (FER) switching field Ef and less hysterisis loss ΔE for application of large displacement actuato r, Ba2+ ionics was employed to control the relative stability between AFEt, FER, and parroelelctrics (PEc) phases in (Pb097-xBaxLa002)(Zr055Sn035Ti01)O3 (0≤x≤02) system. Structural chan ges and electric properties as a function of Barium content x have been investig ated by X-Ray diffraction, dielectric properties, polarization and longitudinal strain measurement. It is observed that AFEt changes to FER, and finally to ferroelectric relaxors(RFE) as Ba content x increases from zer o to 02. Based upon these expermental result, we are able to tailor the AFE-FE switching parameters such as Ef, ΔE and AFEt operating t emperature range ΔT through modifying the Ti/Sn ratio near AFEt/FER phase boundary in the (Pb087Ba01La00 2)(Zr06TiySn04-y)O3 (004 ≤y≤009) system. Finally, a new kind of AFEt ceramics with Ef =16kV/mm,ΔE=085kK/mm, and longitudinal strain x=01%—02% which is appropriate for application of digital actuators has been obtained. Phase dia gram with composition located near AFEt/FER boundary of t he studied system has been determined.
SITE SYMMETRY DETERMINATION AND SELECTIVE EXCITATION SPECTROSCOPY OF Eu3+:ThO2 CRYSTAL
J.C. KRUPA, YIN MIN
2000, 49 (9): 1859-1866. doi: 10.7498/aps.49.1859
Abstract +
The emission spectra, excitation spectra and fluorescence decay curves of Eu3+:ThO2 are reported and analyzed. The Eu3+:ThO2 crystal was grown by the flux technique. Using selective dye laser exci tation at 12K and selection rules, site symmetries of Eu3+ ions in T hO2 are determined as Oh and C3v. Their crystal field levels and lifetimes were measured and tabulated. The dependence of energ y transfer and energy level position on temperature are also discussed.
ANALYTICAL BAND SIMULATION OF ELECTRIC TRANSPORT IN ZnS THIN FILM ELECTROLUMINES CENT DEVICES
ZHAO HUI, HE DA-WEI, WANG YONG-SHENG, XU XU-RONG
2000, 49 (9): 1867-1872. doi: 10.7498/aps.49.1867
Abstract +
The band structure of ZnS calculated from empirical pseudopotential method is fitted by use of polynomials. The density of state and scattering rates are also calculated from these polynomials. Based on these results, electric transport process in ZnS-type thin film electroluminescent devices is simulated through Monte Carlo method. By comparison with other methods, the calculation based on this m odel is as fast as nonparabolic model and as accurate as full band model. Furthe rmore, the influence of band model on simulation result is also investigated. We show that the dispersion relations and density of state are all important in si mulation.
TGS CRYSTAL GROWTH POLYMORPHISM AND SURFACE DIFFUSION GROWTH MECHANISM
SUN DA-LIANG, YU XI-LING, WANG YAN, GU QING-TIAN
2000, 49 (9): 1873-1877. doi: 10.7498/aps.49.1873
Abstract +
Four faces of TGS crystal were chosen to study the growth kinetics. BCF spiral growth mechanism for the surface diffusion model was analyzed using the kinetic data of the four faces. We found it is more important that the growth units enter the surface layer to grow after overcoming the dehydration activation energy, than the process of surface diffusion. Two simple crystal forms of TGS spontaneousnucleation crystals were also observed.
TOPMOST SURFACE AND GROWTH MECHANISM OF BaTiO3 THIN FILM GROWN BY LAS ER MOLECULAR BEAM EPITAXY
HUANG HUI-ZHONG, ZHANG HONG-XIA, CUI DA-FU, CHEN FAN, ZHAO TONG, SHI WEN-SHENG, CHEN ZHENG-HAO, ZHOU YUE-LIANG, LV HUI-BIN, YANG GUO-ZHEN
2000, 49 (9): 1878-1882. doi: 10.7498/aps.49.1878
Abstract +
The BaTiO3 thin film was grown epitaxially on SrTiO3(001) substrate by laser molecular beam epitaxy (laser-MBE). The film growth process w as monitored by in situ reflection high-energy electron diffraction (RHEED), the regular RHEED intensity oscillation from the 0th-Bragg reflection shows an unit cell layer-by-layer growth mode. The crystalline structure and the surface morp hology of the laser-MBE BaTiO3 film were characterized by X-ray diffr action (XRD) and by atomic force microscopy (AFM), respectively. The XRD and AFM results show that laser-MBE BaTiO3 film exhibit the tetragonal c-axi s oriented structure and an atomically smooth surface with a root mean square su rface roughness of 016nm. The topmost surface of the film was studied by angl e-resolved X-ray photoelectron spectroscopy (ARXPS), indicating the laser-MBE Ba TiO3 film is predominantly terminated with TiO2 atomic pla ne. The topmost surface of laser-ablated BaTiO3 film was also analyze d. The film growth mechanism was investigated in atomic scale.
PHOTOCHEMICAL REACTION ON ITO SURFACE INDUCED BY SOFT X-RAY IRRADIATION
LIU LI-MING, XIONG YU-QING, GUO YUN, LI GUAN-BIN, YANG DE-QUAN
2000, 49 (9): 1883-1885. doi: 10.7498/aps.49.1883
Abstract +
ITO surface photochemical reaction induced by soft X-ray (Mg Kα=125360eV) irr adiation is investigated in-situ by XPS technique. The result shows that the con tent of In and Sn in the irradiated area goes up with the increasing irradiation time, while that of O falls. The changes of In3d, Sn3d XPS spectra and the Auge r Parameter of In, Sn suggest that there is chemical reaction due to X-ray irrad iation. It can be concluded that more photo-dissociation happens to In element a ccording to the obvious fact that there exists sub-oxidized state of In after ex posure to X-ray. The photochemical reaction mechanism induced by soft X-ray irra diation is discussed.
SQUEEZE FLOW VISCOELASTICITY OF ELECTRORHEOLOGICAL FLUIDS BASED ON MICROCRYSTAL LINE CELLULOSE
WANG ZUO-WEI, ZHOU LU-WEI, LIU LI-WEI, WANG ZHI-JIN, GAO GUANG-JUN, LIU XIAO-JUN
2000, 49 (9): 1886-1891. doi: 10.7498/aps.49.1886
Abstract +
Dynamic viscoelasticity of electrorheological fluids based on microcrystalline c ellulose/castor oil suspensions was experimentally investigated in squeeze flow. The dependence of storage modulus G′and loss modulus G″parallel to external e lectric field on electric fields and strain amplitudes is presented. The experim ents show that, when external electric field is higher than the critical field, the viscoelasticity of the ER fluids converts from linear to nonlinear, and the ER fluids transfer from solid-like state to fluid state with the growth of strai n amplitude. The influences of strain amplitude and oscillatory frequency on the nonlinearity of viscoelasticity were also studied.
LETTERS
MAGNETORESISTANCE PROPERTIES IN QUASI-TWO DIMENSIONAL CHARGE-DENSITY WAVE COMPOU ND (PO2)4(WO3)2m(m=6)
TIAN MING-LIANG, LI SHI-YAN, CAO QIANG, YUE SONG, ZHANG YU-HENG, SHI JING
2000, 49 (9): 1892-1896. doi: 10.7498/aps.49.1892
Abstract +
Temperature dependence of magnetoresistance in the range of 2—300K and the Δρ /ρ0-B relation at 2K were measured in quasi-two dimensional charge- density wave compound (PO2)4(WO3)2m( m=6). The enhancement of the magnetoresistance at low temperatures was analyzed by use of the magnetic breakdown model. The first Peierls energy gap in the char ge-density wave states was estimated to be about 3.0meV.
STUDING ON ELECTROMAGNETIC CHARACTERS OF Fe/Al2O3/Fe TUNNE LING JUNCTIONS
XU QING-YU, NI GANG, SANG HAI, DU YOU-WEI, LIU CUN-YE
2000, 49 (9): 1897-1900. doi: 10.7498/aps.49.1897
Abstract +
Using ion-beam-sputtering technique, Fe/Al2O3/Fe magnetic tunneling junctions (MTJ) were fabricated. Tunneling magnetoresistance (TMR) eff ect of MTJ samples has been successfully studied. The chemical composition and t he microstructural characteristics of hard-and soft-magnetic layers, insulating layer, and interface of MTJ were analyzed by X-ray photoelectron spectroscopy an d Atomic force microscopy. The dependence of MR effect on microstructure, chemic al composition, conductance, and I-V characteristic of the samples are also di scussed.