Vol. 46, No. 8 (1997)
1997-04-20
GENERAL
1997, 46 (8): 1457-1463.
doi: 10.7498/aps.46.1457
Abstract +
In this paper,the Fife's scaling is used to deal with the three dimensional eikonal equation.Firstly,we put the eikonal equation in the frame of the Fife scaling and obtain the expected scroll waves.Secondly,we directly use the Fife's scaling to perturb the eikonal equation and obtain the similar result.The results of two different methods are essentially the same and the patterns have been observed in the BZ reaction.
1997, 46 (8): 1464-1472.
doi: 10.7498/aps.46.1464
Abstract +
With a model relaxation oscillator and its corresponding discontinuous map,we show that the covering effect of the transient set can produce three kinds of regions:(1) stable chaotic region where all the possible periodic windows are erased,therefore chaotic trajectories are structurally stable;(2) complete phase locking region where chaos is suppressed,only periodic motion is permitted;(3) quasiperiodic region where chaos is suppressed,only quasiperiodic motion or periodic motion with marginal stability is allowed.These ideas are then used to explain the observed stable chaotic regions and the complete phase locking regions in a practical electronic relaxation oscillator.
ATOMIC AND MOLECULAR PHYSICS
1997, 46 (8): 1473-1478.
doi: 10.7498/aps.46.1473
Abstract +
Combing the techniques of supersonic molecular beam and vacuum ultraviolet synchrotron radiation photoionization time-of-flight mass spectroscopy,we have measured the photoionization efficiency(PIE)curves of ions from (CH3I)n(n=1,2,3,4)cluster molecules and obtained the adiabatic ionization potentials of (CH3I)n+(n =1,2,3,4) and appearance potentials of the fragment ions.From these data,bond energies D0 of the related molecules or molecule ions have been evaluated.Several autoionization structures of CH3I in the PIE curve of CH3I+ have been observed and 4 Rydberg series,ns,npσ, npπ and nd, converging to CH3I+(2Ｅ1/2),are identified.
CLASSICAL AREA OF PHENOMENOLOGY
1997, 46 (8): 1479-1486.
doi: 10.7498/aps.46.1479
Abstract +
A model is presented for the magnetically confined sputtering discharge which is being examined to be used in metal vapor lasers.The current-density and spatial dependences of the metal vapor density are described.The predictions are found to be in agreement with the- experiments.
1997, 46 (8): 1487-1492.
doi: 10.7498/aps.46.1487
Abstract +
Holographic photon-gated spectral hole burning and image storage were performed in meso-phenyl-tetrabenzoporphyrinato-zinc/aromatic cyanide systems.In holographic spectral hole burning,the signal to noise ratio is improved considerably.Based on photon-gated persistent spectral hole burning,photon-gated frequency-selective multiple images were recorded and recalled successfully as holograms in the material.
1997, 46 (8): 1493-1499.
doi: 10.7498/aps.46.1493
Abstract +
Based on the established theory of photoinduced exciton bleaching of the polymers with nondegenerated ground state,we calculated the transient mirrorless optical bistability of photoexcitation and relaxation processes in the polymers.The results show that the transient saturation absorption mirrorless optical bistabilities and the increasing absorption mirrorless optical bistabilities can be obtained from the ultrafast excitation and relaxation processes in the polymers with nondegenerate ground state,and the switching time of the optical bistabilities is of the order of fs or ps.With the increase of the delay time of the probe pulse relative to pump pulse,the nature of mirrorless optical bistability can change from the saturation absorption optical bistability to increasing absorption optical bistability,and the rate of change is proportional to the speed of relaxation of the photoinduced exciton.
1997, 46 (8): 1500-1507.
doi: 10.7498/aps.46.1500
Abstract +
The electrical property and shear strength of a single chain formed in silicone oil is studied under dc electrical field,which consists of small humidited glass spheres (diameter is 200—220μm).It is found that the current flowing through a static (no shear) single chain increases with the increase in electrical field strength.The current and the yield shear stress is almost independent of the number (3—5) of the glass spheres to form the chain.The measured average current density and yield shear stress of a single chain versus the field strength is fairly agreement with that predicted theoretically.
1997, 46 (8): 1508-1516.
doi: 10.7498/aps.46.1508
Abstract +
We have developed a lattice-Boltzmann model from previous models for multiphase fluid flows to simulate Rayleigh-Taylor instability.A force has been introduced and a 9-velocity square lattice is used.The conservation equation of total mass and momentum can be derived using Chapman-Enskog multiscale expansions.Using this model we have obtained the linear growth and nonlinear growth of bubbles and the mushrooms produced by Rayleigh-Taylor instability.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1997, 46 (8): 1517-1524.
doi: 10.7498/aps.46.1517
Abstract +
The physical process of using ECRH to produce sloshing electrons and to form tandem mirror thermal barrier is calculated by means of Fokker Planck kinetic equation.The results show that (1)under certain conditions,the sloshing electron plasma configuration has been formed,the density ratios of which neh(Zr)/neh(0)=2.15 and the potential dip ΔФ=16.5V have also been formed;(2)there are three stages consisting of rapid establishment,gradual decrease and stable equilibrium in the establishment of potiential dip,which result from the coaction of ECRH,collision scattering and trapped ions.
1997, 46 (8): 1525-1534.
doi: 10.7498/aps.46.1525
Abstract +
The helical instability of an arc column with electrical conductivity of the parabolic distribution and transparent radiation of the parabolic distribution is discussed in axial magnetic field.The magnetohydrodynamic equations serve as the strarting point of the theory.In an electrostatic approximation and a linear time dependent perturbation theory,the perturbation equations for the arc column movement are deduced.Solutions of these equations are obtained analytically,from which the stability limit of the cylindrical arc and the growth rate of the helical instability are given.In comparision the results with those of current distribution without radiation,it is found that the radiation in the small middle arc increases the instability.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1997, 46 (8): 1535-1542.
doi: 10.7498/aps.46.1535
Abstract +
The atomic structure of several surfaces has been investigated on the basis of the real space patterns formed by forward scattering of medium energy electrons from the surface.The images of the Cu(111) surface show not only that the surface has the three fold symmetry but also that the fcc stacking sequence persists up to the topmost atomic layer.The images of the Si(111)(31/2×31/2)R30°-In surface support that In atoms occupy the T4 sites on the surface,rather than the H3 sites.In the case of Ge(111)(31/2×31/2)R30°-Ag surface the images indicate that the honeycomb chained triangle (HCT) model is correct.The success of these applications shows that reliable structural information of surfaces can be obtained quite straightforward by means of forward scattering of medium energy electrons,instead of via complicated calculations such as involved in LEED crystallography.
1997, 46 (8): 1543-1551.
doi: 10.7498/aps.46.1543
Abstract +
AFM and PL are adopted to study the morphological and photoluminescent characteristics of a series of porous silicon (PS) samples etched with direct current and pulsed current.The results of AFM indicate that there are many “hillocks” at the surface of PS samples and the microstructure of PS samples is quite different with different etching modes.The amount of the small Si particles formed by pulsed etching is more than that by direct current etching under the-equivalent etching-conditions and the particles appear more protruding and sharper by the pulsed etching.Moreover,PL spectra shows that it is easier to get photoluminescent PS samples with higher intensity by using pulsed etching method.The microstructure of PS samples plays a very important role in the generation of photoluminescence of porous silicon.
1997, 46 (8): 1552-1558.
doi: 10.7498/aps.46.1552
Abstract +
In the present paper we report local work function measurements on the Cu(111)-Au and Pt(111)-Ag surfaces using scanning tunneling microscopy (STM).By measuring the response of tunneling current to the variation of the tunneling gap distance a work function image can be obtained simultaneously with a topographic STM image. By means of this technique,we are able to detect the difference between the local work functions of the overlayer and the substrate in both Cu(111)-Au and Pt(111)-Ag cases.Our results show that the local work function of the Au overlayer is between those of Au(111) and Cu(111) surfaces,supporting the results obtained with other techniques. In the case of the Pt(111)-Ag surface the local work function depends on the local thickness of the Ag overlayer.
1997, 46 (8): 1559-1566.
doi: 10.7498/aps.46.1559
Abstract +
We have studied the growth of C60 film on GaAs(001) 2×4-β phase surface epitaxially grown by MBE.Due to the delicate equilibrium between the interaction of C60 molecules and the interaction of C60 molecule with the substrate,the toplayer of C60 film,unlike that on the metal and silicon substrate,shows a non-close packed structure.The facet structure of C60 film exhibits that the top-two layers are hcp but the others are fcc,which implies an existence of the phase-transition from hcp to fcc structure in the film growth.The measurement results that the lattice constant of fcc is 1.13 nm,larger of 13% than that of C60 crystal,and hcp is not ideal which is compressed along c-axis.The strain in C60 film and the minimum of the total energy should be responsible for the existence of the phase-transition.On GaAs(001)-c(4×4) surface,the structure of C60 film shows fcc(111) surface and the film grows in three-dimensional mode which is quite different from that on other substrates.
1997, 46 (8): 1567-1572.
doi: 10.7498/aps.46.1567
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In this paper,we present the experimental observation of the deformed carbon nanotubes,using transmission electron microscopy (TEM).The deformations obsorred include both the radial deformation and the axial deformation. A proposed model can explain qualitatively the occurrence of the deformations of the carbon nanotube in a deposit by arc discharge between two proximate electrodes in argon atmosphere.
1997, 46 (8): 1573-1579.
doi: 10.7498/aps.46.1573
Abstract +
A universal method of calculating extinction factor is developed,which is to introduce a primary extinction factor into the secondary extinction method based on the exact solutions of Darwin transfer equations.As an example,the extinction factors of large LiF are calculated and discussed.The average error factor R is lesser than that got by the method which don't inclued primary extinction.
1997, 46 (8): 1580-1584.
doi: 10.7498/aps.46.1580
Abstract +
Distribution and migration characteristics of fluorine in poly-Si gate on BF2+ implanted poly-Si gate with an energy of 80 keV and doses of 2×1015 cm-2 under conventional thermal annealing has been analyzed systematically and deeply by SIMS.Migration of fluorine in poly-Si gate exists not only diffusion mechanism,but also absorption and emission mechanism,and experiment results are explained successfully.
1997, 46 (8): 1585-1592.
doi: 10.7498/aps.46.1585
Abstract +
Foamed aluminium (Al) specimens have been prepared by powder metallurgy foaming technique.At room temperature,variations of its internal friction vs porosity,frequency and strain amplitude were measured systematically.The results indicate that internal friction of foamed Al has such characteristics as follows.It increases with increasing porosity and with decreasing pore size.At lower frequencies,it is independent of frequency;it-has a normal amplitude effect.The damping mechanism of foamed Al has been studied.According to the damping mechanism of foamed Al,the experimental results have been explained with some success.
1997, 46 (8): 1593-1597.
doi: 10.7498/aps.46.1593
Abstract +
Photorefractive beam fanning was observed in almost all photorefractive crystals with a nonlocal nonlinearity. Recently we observed experimentally symmetrical beam fanning in photorefractive crystal (LiNbO3:Fe) with a local nonlinear response.Based on forward degenerate three-wave interaction,we presented a theoretical study of the symmetrical beam fanning.
1997, 46 (8): 1598-1604.
doi: 10.7498/aps.46.1598
Abstract +
Based on the s-d interaction model,we consider the influence of s-f exchange effect on the electron-phonon coupling and discuss the specific heat of conducting electron in a rare earth metal.The results of calculation show that the specific heat of conducting electron can be written as γ＝γ0＋γep＋γex＋γs-f, where γ0 =(πkB/?kF)2m ,γep=γ0λep ,γex=γ0λex ,γs-f =γ0λs-f;here ep =e-p coupling,ex=exchange,s-f=s-f exchange.
1997, 46 (8): 1605-1612.
doi: 10.7498/aps.46.1605
Abstract +
A 200nm Ti film was deposited on a polished mullite ceramic substrate at 200℃ by electron beam evaporation,and annealed under high vacuum conditions.Secondary ion mass spectrometry (SIMS),Auger electron spectroscopy (AES) and X-ray diffraction measurement (XRD) were employed to probe the solid interfacial reaction between Ti and mullite from 200—650℃ for the first time.The results show that the first deposited Ti atoms have formed Ti—O bond with O on mullite surface during the deposition,and trace elemental Al and Si atoms have been segregated,but interfacial range is very narrow.It was broadened a little after the sample annealed at 450℃ for an hour.Interfacial reaction happened violently when the annealing temperature was 650℃ for an hour,and the sample mainly consisted of four laminated structures which in turn were TiO+Ti,Ti3Al,Ti3Al+TiSi2 and mullite ceramic substrate.
1997, 46 (8): 1613-1617.
doi: 10.7498/aps.46.1613
Abstract +
A Series of samples of ultra thin AlGaAs films grown on GaAs(100) substrate by MBE are studied by photomodulated reflectance (PR)spectroscopy in ultra high vacuum chamber.More than one peak are observed for samples with thickness less than 35nm,but only one peak is observed for 100nm thick sample,The position and width of these peaks change with sample thickness.The experimental results are well explained by step potential model.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1997, 46 (8): 1618-1624.
doi: 10.7498/aps.46.1618
Abstract +
The general correlation factor for the two dimensional and the quasi two dimensional electron gas is presented based on the Bohm Pines theory.The pair correlation function,the exchange energies and the correlation energies of electrons in the AlxGa1-x As GaAs quantum wells are obtained employed the correlation basis function method.
1997, 46 (8): 1625-1630.
doi: 10.7498/aps.46.1625
Abstract +
The zero field splitting (ZFS) of Fe3+ ions at the tetragonal symmetry sites in the fluoroperovskites AMF3 doped with Fe3+ is analysed and shown the existence of the crystal defects and lattice distortion.The ZFS parameters are investigated as a function of the defect induced lattice distortion parameters.The distortion parameters are obtained by adjusting them to fit the experimental ZFS data.
1997, 46 (8): 1631-1635.
doi: 10.7498/aps.46.1631
Abstract +
A hybrid conduction analysis method mixed with multi carrier fitting procedure and mobility spectrum is present to analyze the experimental Hall and resistivity data of MBE grown Hg1-xCdxTe samples as a function of magnetic field.This method enables the conductivity contribution of bulk electron to separated from that of interface electron.Applications to temperature dependent Hall and resistivity data confirm that the procedure may be regarded accurate and reliable one.The method seems to be a suitable tool for the routine electrical characterization of semiconductor materials and devices.
1997, 46 (8): 1636-1644.
doi: 10.7498/aps.46.1636
Abstract +
A hetero-quantum-dots (HQD) model for hydrogenated nanocystalline silicon films (nc-Si∶H) is proposed. The main contents of our model are: (i) the nanocrystalline grains and their amorphous conterparts have very different band gap and band structures. As a result, they form heterojunction like structures in the interface regions, where the band offset effects dramatically reduce the activation energy and the grains act like quantum dots; (ii) in the presence of an external field, the activated electrons in the quantum dots conduct via quantum tunneling through the interface barriers. By means of the HQD model, we have identified the conduction of nc-Si∶H as thermal assisted tunneling process. Our results show that there are two distinctive regimes for the conductivity of nc-Si∶H:(1) low temperature regime,where there is a simple activation energy ΔE; (2) high temperature regime, where ΔE is enhanced by the temperature effect of the electronic tunneling in the nanoscale particales. The theory is in good agreement with the experiments. Finally, we propose a perfect conductivity formula for nc-Si∶H films.
1997, 46 (8): 1645-1651.
doi: 10.7498/aps.46.1645
Abstract +
Green/blue light emission with peak position around 2.3—2.4eV at room temperature was observed from Si nanocrystals embedded in silicon oxide films. The effects of thermal annealing on the structure, silicon core level and photoluminescence of silicon oxide films with nanostructures were studied. PL spectra consisted of peaks of 1.86 and 2.38eV, which were independent of annealing temperature Ta. Silicon and SiO2 phases were separated in the annealing temperature range. Both PL intensity and the amount of Si4+ increased repidly as Ta>750℃. From our observation, the origin of green/blue light emission is suggested to be related to the defects at the interface and in the SiOx network.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1997, 46 (8): 1652-1657.
doi: 10.7498/aps.46.1652
Abstract +
The electric conductivity changes markedly when titania is irradited by a proper-fluence excimer laser, it changes from insulator to semiconductor at room temperature, and its color changes too. Several titania samples before and after irradiation are studied with XRD, XPS and microscopic analyses. It is observed that the changes takes place when proper-fluence excimer laser pulse irradites the surface of titania and the temperature of the surface rises quickly. A thin layer of the irradited area melts quickly and soon resolidifies. This leads oxygen in titania to vacate partly, so the stoichiometry of the sample deviates from the normal value. The laser fluence threshold is estimated by the equation of heat transfer and the result agrees approximately with the experiment.
1997, 46 (8): 1658-1664.
doi: 10.7498/aps.46.1658
Abstract +
We studied the changes of both the surface morphology and the surface oxidation state of metal Sn thin films due to oxidation at enhanced temperatures(300—550℃). With atomic force microscopy, it was observed that the metal Sn thin film and the oxidized metal Sn thin films consisted of a great number of square-metallic crystallites and spherical-oxidized agglomerates, respectively. Such changes in the surface morphologies resulting from the oxidation process suggested that the oxidation of the square-metallic crystallites at the enhanced temperatures was anisotropic. By using X-ray photoelectron spectroscope, it was found that there were some oxygen particles adsorbed on both the surfaces of the metal Sn thin films and the oxidized metal Sn thin films. Furthermore, the forms of the adsorbed oxygen particles depended on the surface oxidation states.
