Vol. 42, No. 8 (1993)
1993-04-20
GENERAL
1993, 42 (8): 1199-1204.
doi: 10.7498/aps.42.1199
Abstract +
Differentail realizations of the SPL(2,1) superalgebra on the spaces of homogeneous and inhomogeneous polynomials and the corresponding boson-fermion realizations are studied.
1993, 42 (8): 1205-1209.
doi: 10.7498/aps.42.1205
Abstract +
In this paper, we study the chaotic behavior of a two-photon quantum optical model. The results show that the model can exhibit chaotic behavior without any perturbation or modulation terms. The chaos is characterized by Fourier analysis and the maximal Lyapunov exponent. The properties of the chaotic behavior are also discussed. We proved that the two-photon J-C model, which contains the rotating-wave approximation, cannot exhibit chaotic behavior.
NUCLEAR PHYSICS
1993, 42 (8): 1210-1215.
doi: 10.7498/aps.42.1210
Abstract +
The phase transition of two-flavor quark matter into strange matter in the interior of a neutron star is studied. It is shown that the timescale of the transition is less than 0.1μs and the s-quark semileptonic processes are of significance in neutrino emission during the transition. Owing to these processes, the transition in a whole neutron star will liberate several 1051 erg of energy as a neutrino burst.
ATOMIC AND MOLECULAR PHYSICS
1993, 42 (8): 1216-1222.
doi: 10.7498/aps.42.1216
Abstract +
The key to the treatment of the resonance radiation imprisonment lies in the solution to Holstein's equation. A new method to solve Holstein's equation is proposed in this paper, which integrates the equation directly by means of operator calculation and results in a formula for the excited particles in an infinite series in an integral operator. Our study on the behavior of the high-ordercoefficients of this series leads to the success in overcoming the difficulty to obtain the sum of infinite terms, and a formula of finite terms under any given precision is acquired, which applies to the whole time scale.
CLASSICAL AREA OF PHENOMENOLOGY
1993, 42 (8): 1223-1230.
doi: 10.7498/aps.42.1223
Abstract +
From the equation for the matrix elements of the field density in the two-photon process, with the aid of the generation function method, the exact analytical expressions of the amplitude N-power squeezing generating in two-photon absorption process are derived. The variation of the amplitude N-power squeezing with the diemensionless time τ, power exponent N, the phase θ and the average number of photons of the incident field are discussed. It have been shown that the amplitude N-power squeezing for different power exponents N is independent of each other, the two-photon absorption process is one of effective ways to generate the amplitude N-power squeezing.
1993, 42 (8): 1231-1235.
doi: 10.7498/aps.42.1231
Abstract +
An energy-level system with upper-level coherence driven by an external field is investigated. It is shown that a laser may develop without the need of population inversion in any state (bare or dressed states).
1993, 42 (8): 1236-1244.
doi: 10.7498/aps.42.1236
Abstract +
Dynamics of reverse saturable absorption (RSA) and optical limiting (OL) in C60 medium are studied in detail employing rate equation theory. Experimental results of RSA and OL in C60toluene solution with a Q-switched frequency-double YAG laser agree well with the theoretical simulations. The contribution of each energy level of C60 molecule to RSA and the influence of different laser wavelength and pulse duration on RSA and OL are also dicussed.
1993, 42 (8): 1245-1251.
doi: 10.7498/aps.42.1245
Abstract +
A phase-only optical system can implement the wavefront transformation from a rotational symmetric beam to another rotational symmetric beam, which is composed of two phase-only diffraction elements. Under the Fresnel diffraction approximation, the optical transform system can be designed with the aid of the stationary phase method and the input-output method with a high accuracy.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1993, 42 (8): 1252-1256.
doi: 10.7498/aps.42.1252
Abstract +
This paper presents the measurement methods and the experimental results of X-ray conversion efficiency in 1. 2 keV region from Cu and NaF plasma produced by 1.06 and 0.53μm laser. These results showed that X ray conversion efficiency in Cu plasma is 4-5 times as high as that in NaF plasma with the laser intensity in 1×1013—1×1014W·cm-2 and wavelength of 1. 06 and 0. 53μm. The X-ray conversion efficiencies in Cu and NaF plasma produced by 0. 53μm laser are about 2 times as high as that by 1.06μm laser.
1993, 42 (8): 1257-1265.
doi: 10.7498/aps.42.1257
Abstract +
The effect of electron cyclotron wave on trapped electrons and runaway electrons in mirror plasma is discussed in the context of the Lagrangian formulism of the guiding center for charged particle developed by Littlejohn. The condition for transition between trapped electrons and runaway electrons is given, their transition probabilities are evaluated as well.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1993, 42 (8): 1266-1271.
doi: 10.7498/aps.42.1266
Abstract +
The STM images of NaCl microcrystal at room temperature have been studied in the air. The results show that the ionic conductivity plays a crucial role in the image formation. The resolution of the microcrystals is restricted due to surface condensation of water molecules on the sample, and the phenomenon of "dragging effect" appears on the NaCl images. The effects of bias voltage and humidity to the tunneling process are also discussed.
1993, 42 (8): 1272-1277.
doi: 10.7498/aps.42.1272
Abstract +
By using the crystallization method, nanocrystalline (Fe0.99Cu0.01)78Si9B13 alloys were synthesized. The relationship between microhardness Hv and grain size d was proved to obey Hall-Petch relation. By means of M?ssbauer spectroscopy, the distribution of metalloids Si and B and their influence on electronic structure of crystallized phases were also investigated.
1993, 42 (8): 1278-1289.
doi: 10.7498/aps.42.1278
Abstract +
By means of dynamics approach, the wetting transitions of a simple fluid confined between parallel walls that exert different surface fields have been investigated. The states of the system are sensitive to the surface fields and wall separation. In some cases, even if the difference of two walls is very small, the phenomenon that one wall is wet and the other is non-wet may occur. The wetting transitions may be first order of second order.
1993, 42 (8): 1290-1296.
doi: 10.7498/aps.42.1290
Abstract +
In the present paper, the interfacial reactions at the interfaces of the Sn/Si system have been studied by means of tunable-sampling-depth electron energy loss spectroscopy (TELS) in conjunction with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). It is found that, depending on the orientation of the silicon substrates, the interfacial reactions are qualitatively different. No intermixing of Sn with Si occurs at the as-deposited Sn/Si (111) interfaces and the Sn/Si (111) interfaces annealed at temperatures lower than 400℃. However, Sn intermixes with Si at the Sn/Si (111) interfaces annealed at temperatures between 400 adn 700℃, forming a Sn/Si intermixing layer with a maximum thickness of about 1nm. The bulk plasmon peak of this intermixed layer on the ELS curve is at 15. 5eV. No detectable intermixing of Sn with Si has been found at the Sn/Si (001) interfaces annealed at any temperature. Annealing at increasing temperatures only makes the homogeneous Sn layer to become islands, and the islands become smaller and eventually disappear at a temperature higher than 1000℃. A prolonged annealing at 550℃ gives rise to the appearance of (113) facets on the Sn/Si (001) surface, as shown by the 'moving spots' on the LEED pattern.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1993, 42 (8): 1297-1303.
doi: 10.7498/aps.42.1297
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The electronic structures of oxygen vacancies and substitutional divalent and trivalent cobalt ions in cubic yttria stablilized zirconia crystals were calculated by the discrete-variation-al (DV)-Xα method. Various clusters account for different configurations of the oxygen vacancies and different coordinations of the cobalt ions. The oneelecton eigenvalues and charge distributions of the clusters were given. The energies of optical transitions were obtained by transition-state calculations, and compared with available experimental date. The effects of composition and thermal processing on the absoption spectra of the crystal are discussed.
1993, 42 (8): 1304-1310.
doi: 10.7498/aps.42.1304
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The deep centers in Si-implanted LEC semi-insulator gallium arsenide have been carefully studied using the deep level transient spectroscopy (DLTS) technique. The results are as follows. The four majority carrier traps,E01 ,E02,E03 and E04 have been observed in the active regions of the Si-implanted LEC semi-insulator gallium arsenide after high temperature an-nealling, and their electron apparent activation energies are 0.298, 0.341, 0. 555 and 0. 821 eV respectively. The E04 trap is related to the EL2. The activation energy of the electron capture cross section of E04 is 0. 119 eV Three minority carrier (hole) traps have been newly found in the same active regions. The hole apparent activation energy of the H03 trap is 0. 713 eV and its concentration is about 2. 8×1016cm-3.
1993, 42 (8): 1311-1316.
doi: 10.7498/aps.42.1311
Abstract +
The stability of soliton pairs and the electronic energy level structures in a doped poly-acetylene chain have been studied under natural boundary conditiono. In the Itamiltanian usel an end point potential was added to the SHH model, and the screened Coulomb potential of impurities and e-e interaetion on the tattice points were also indndelincluded. The caleulated results Show that, as the range of coulomb interaction is long enongh, stable soliton pairs are formel in the chain, and the stability is enlanced by the influce of the ends the gap width becomes narrow with the increase of chain length. But the deplndence of transition energg from soliton level to band bottom on chain length is not very signicant.
1993, 42 (8): 1317-1323.
doi: 10.7498/aps.42.1317
Abstract +
The electronic structures of short period (Si)n/(Ge)m Strainedlayer superlattices (SLS's) are calculated using empirical tight-binding method. The results indicate that due to the zone-folding, only the SLS's with n+m=10 have the posibility to form direct band gap. For SLS's with n+m=10, the type of energy gap is determined by the relative energies of conduction band valleys at Γ, N, and Δ. However, the Ge layers number and the composition of substrate play an important role. For (Si)6/(Ge)4 and (Si)8/(Ge)2 SLS's grown on Si1-xGex substrate, direct or quasidirect band gap could be got for the substrate composition 0.4≤x≤1.0 For (Si)4/(Ge)6, direct gap could be obtained only for 0.3≤x≤0.6, and in (Si)2/(Ge)8 SLS's the gap could not be direct for all substrate composition.
1993, 42 (8): 1324-1332.
doi: 10.7498/aps.42.1324
Abstract +
Behavior of gold in the Si/SiO2 interface region has been investigated using deep level transient spectroscopy (DLTS) in the MOS structures made on p-type silicon wafers with orientation. The results are as follows. A new defect, Au-Hit(0.445), has been observed at the interface, which is the incorporation of gold atom by the interaction with the interface defect, Hit(0.494). A continuous spectrum of the interface states related to gold has also been measured in the lower half of Si band gap, which are acceptors, and the physical mechanism of the positive shift of the flat band voltage of the MOS structure caused by gold doping ean be explained in terms of these gap states. The profile of the gold donors in the silicon near the interface has been obtained, which is not monotonically increase towards the surface but exhibits a maximum at 0.37μm from the surface.
1993, 42 (8): 1333-1339.
doi: 10.7498/aps.42.1333
Abstract +
The interface formation of room temperature deporsited Mn on GaAs(100)(4×1) surface was studied by low energy electron diffraction (LEED), X-ray photoelectron spec-troscopy (XPS), electron energy loss spectroscopy (EELS) and ultra-violet photoelectron spectroscopy (UPS). It was found that above the Mn coverage of 0. 25 nm, the LEED pattern disappeared completely, which indicated that the Mn overlayer did not form single crystalline structure. The layer-by-layer growth mode at the initial stage was proved by the results of both LEED and EELS. By careful study of the intensities and line shapes of the Ga2p3/2 and As2p3/2 core level photoemission spectra, we observed that the exchange reaction between the deposited Mn and the substrate occurred at very early stage. The Ga atoms released by the exchange reaction distributed within a region about 3 nm above the original interface, while the As atoms which combined with Mn to form As-Mn compound segregated on the top of Mn overlayer. The layer-by-layer growth mode persisted until the latest stage of the deposition. Some of the above results were intuitively confirmed by UPS measurements.
1993, 42 (8): 1340-1345.
doi: 10.7498/aps.42.1340
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In this paper, we report the in-situ study of the dependence of electrical resistivity of magnetron sputtering Mo film on the thickness. We measured the electrical resistivity of Mo film by vacuum measurement. After theoretical computer fitting, we obtained the t heoretical curve of the dependence of resistivity of Mo film on the thickness. We compared the theoretical curve with the experimental curve, the results show that when the thickness is large, there is a very small diversity between the theory of Fuchs-Sordbeimer of resistivity and the present thickness dependence of electrical resistivity. If the effect of grain boundary is considered, the result will agree with the Fuchs-Sordbeimer theory very well in small thickness. We also found that the process of conductance is the thermal electron emission, when the film is not a successive film.
1993, 42 (8): 1346-1351.
doi: 10.7498/aps.42.1346
Abstract +
This work studies the effect and mechanism of slow neutron irradiation of low fluence (～108n/cm2) in normal resistivity of Y and Bi system and the doped high Tc superconductors. The experimental results indicate that the normal resistivity R not only follows the law that R is increasing exponentially with the enhancement of fluence φn, but also decreases greatly after irradiation of slow neutron with low fluence.
1993, 42 (8): 1352-1355.
doi: 10.7498/aps.42.1352
Abstract +
The dynamic theory for disordered superconductivity is suggested based on the fracton-electron interaction. It has been demonstrated that electrons in disordered superconductors can feel an attractive interaction by exchange of virtual fractons. A normal state is unstable with respect to such an interaction, and a superconducting state is formed through the association of electrons in pairs with opposite wave vectors and spins. The critical temperature for percolation superconducting model can be derived from this theory.
1993, 42 (8): 1356-1360.
doi: 10.7498/aps.42.1356
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In this paper, we propose a bimodal distribution of random neuronal activity threshold with different probabilities, to consider the influences on the retrieval properties of neural network. It is shown that the system successfully retrieves information even if the number of stored patterns exceeds the critical value of the pure Hopfield model.
1993, 42 (8): 1361-1369.
doi: 10.7498/aps.42.1361
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The magnetic properties are reported for amorphous NdxFe1-x films prepared by flash e-vaporation at 77K. The result indicates that Nd is nearly random distributed with a small net moment parallel to the Fe moments which posseses a ferromagnetic alignment. The distribution angle of the Nd-atomic moments increases slightly with increasing x. The ordering temperature Tc is dependent on applied field and the values of Tc from Arrott-plot or other evaluation methods are different. This can be attributed to exsistence of clusters with different Tc in the film. The exchange interaction, but not the spontaneous magnetisation, is strongly influenced by the preparation conditions.
1993, 42 (8): 1370-1374.
doi: 10.7498/aps.42.1370
Abstract +
The films of copolymers of vinylidene fluoride with trifluoroethylene (VDF/TrFE) with different crystallinity were prepared by four methods, i. e. , as-cast, quenching in liquid nitro-gen, slow-cooling and annealing at 140℃. The complex dielectric constants were measured using an improved dielectric relaxation spectrometer whose precision increased to 2‰ from the original 1%. The dielectric relaxation of noncrystalline regions was found in accordance with the dielectric frequency spectra of quenched sample that the crystallinity was 20% below room temperature. Thereby, the relationship between the glass transition temperature and the component of copolymers was got.
