Vol. 38, No. 3 (1989)
1989-02-05
CONTENT
1989, 38 (3): 349-356.
doi: 10.7498/aps.38.349
Abstract +
We had obtained the semiempirical functions for describing the interaction properties in the ground state of Cu by using the Embedded Atom Method (EAM). In this work, The formula of surface Yorce constants between planes are derived, the force constants between planes of Cu (100), (111) and (110) surfaces are then calculated, which show that the EAM can distinguish the difference of interatomic interactions in the bulk and near the surface, and distinguish the difference of interatomic interactions near different structural surfaces. The calculated force constants lead to good agreement between the projected state densities of surface vibrations calculated by Recursion Method and the experimental results of electron-energy-loss-spectroscopy.
1989, 38 (3): 357-365.
doi: 10.7498/aps.38.357
Abstract +
We have studied the surface relaxation of GaAs (110) with Low-Energy-Electron-Diffra-cion. We find that the best agreemet between theory and experiment is obtained for such a structure in which the As atoms are tilted outward by 0.10±0.02? and the Ga atoms are tilted inward by 0.55±0.02?, with an angle of rotation (ω) of 27.32°±0.24°, keeping the bond length at surface As-Ga unchanged and a Ga to secondlayer spcing d2= 1.45±0.01?and the second-layer Ga to third-layer spcing d3 = 2.01±0.01?. For this structure, the As back bond length lAs =2.43±0.01? (contracted 0.56%) and the Ga back bood length lGa=2.235±0.004?(contracted 8.0%)
1989, 38 (3): 366-375.
doi: 10.7498/aps.38.366
Abstract +
The envelope function approximation was generalized to calculate the electron subbands and wave functions of quasiperiodic semiconductor superlattices (QSS) within rational approximation, for nonzero K⊥ (the wave vector perpendicular to the axis of the QSS). For K⊥= 0, the electron subbands and wave functions are calculated for InAs/ GaSb QSS up to the generation number m =9 and for GaAs/AlxGa1-xAs QSS up to m = 6. For InAs/GaSb QSS, the influence of valence band states on conduction band state is strong. The dependences of the energies and band widths of electron subbands on K⊥ are obtained for m = 5 and 6. A theoretical method is proposed to calculate the intersubband collective excitations of the type-I QSS by means of the above results.
1989, 38 (3): 376-384.
doi: 10.7498/aps.38.376
Abstract +
A new trap-assisted two-step tunneling model is proposed to explain the conduction enhancement characteristics and conduction mechanism in heavily-nitrided oxide films. A theoretical calculation is carried out to fit the theory to the experimental results. The trap density and trap energy level are found to be in the range of 1.2×1019-7.2×1020cm-3 and 2.46-2.56 eV respectively. These results agree satisfactorily with the Auger spectroscopic data. Furthermore, this model can also be applied MNOS structure or MIS devices with other traps.
1989, 38 (3): 385-393.
doi: 10.7498/aps.38.385
Abstract +
The effect of an electric field on the subbands and excitons in a GaAs/Ga1-xAlxAs quantum well is studied by using a finite-potential-barrier model. The subbands of electrons and holes and the binding energies of excitons have been calculated for GaAs/Al0.34 Ga0.66 As quantum well (L = 105?) in electric field ranging from O to 1.2×105 V/cm. Based on these, the electron-hole overlap functions and the energy shifts of excitons corresponding to different subbands are obtained, they agree well with experimental results.
1989, 38 (3): 394-398.
doi: 10.7498/aps.38.394
Abstract +
The growth behavior during silicon molecular beam epitaxy on Si(lll) is observed by measuring the intensity oscillation of reflection high energy electron diffraction. The oscillation behaves as what is expected with bilayer model. The characteristics of damping and recovery of intensity oscillation during Si molecular beam epitaxy growth on Si(lll) are different from those on Si(100), but are very similar to those during GaAs molecular beam epitaxy growth.
1989, 38 (3): 399-406.
doi: 10.7498/aps.38.399
Abstract +
The effect of light beam polarization on high accuracy measurements of thin wire diameters has been studied. The experimental results are given below in brief. The experimental magnitudes of steel wire diameters vary sinusoidally with the angle between the direction of light vibration and the wire axis. The experimental value obtained with parallel polarization, (i.e., its vibration being parallel to the wire axis) is 0.36 μm smaller than that of the perpendicular, case. The experimental results of steel slit width are contrary to that of steel wires. Based on the experiment, the theoretical analyses of the polarization effect are carried out. Taken into account the influence of light reflection on the wire surface and different phase changes of different vibration directions produced in the reflection, the Fraunhofer diffraction patterns are slightly changed, therefore making the measured values different. According to this idea, the analysis for steel wire shows: the theoretical value of thin wire diameter for light vibration parallel to the wire axis is 0.33μm smaller than that of perpendicular vibration, different from the experimental value 0.36 μm by 0.03 μm. For steel slit width, the measured value with the light vibrations parallel to slit edges is 0.19 μm larger than that of perpendicular case, different from the experimental value 0.21μm by 0.02μm. These differences between theory and experiment are close to or smaller than the error of the measurement system, 0.04 μm. Good coincidencl is achieved.
1989, 38 (3): 407-413.
doi: 10.7498/aps.38.407
Abstract +
Generalized oscillator strength density from an initial atomic state nl to final states n＇l＇ or ∈＇l＇ forming a final channel is a function of the energy transfer ∈ and the momentum transfer q. We report our study on the nodal curves in the ∈-q plane, where the matrix element for the generalized oscillator strength density vanishes. For high momentum transfer, the positions of the nodal curves can be obtained by scaling the hydrogenic results. For low momentum transfer, the nodal curves depend strongly on the difference of the quantum defects △μ of the initial and final channels; the topology of the nodal curves for △μ>0 is completely different from the topology for △μ<0.
1989, 38 (3): 414-421.
doi: 10.7498/aps.38.414
Abstract +
Based on the instability criterion of semi-classical Maxwell -Bloch equations of single-mode optical systems, the global distribution of instability region is depicted in △-θ parameter space (△ detuning of the atoms, θ mistuning of the cavity). In the instability region predicted, various bifurcations and chaos are disclosed. We find that chaos may appear in both upper and lower branches of one bistable curve Moreover, a new time-dependent solution coexisting with the stable stationary solution is found.
1989, 38 (3): 422-429.
doi: 10.7498/aps.38.422
Abstract +
In order to characterize the dynamical properties of a fluorescence system under weak excitation regime, flurescence response function and fluorescence transfer function are introduced. Based on these concepts a new theoretical representation of fluorescence dynamics is established. It is then applied to the discussion of some important problems. The results show that the new theory provides an effective method for describing systematically the fluorescence dynamics of complex systems, in which the energy transfer processes take place.
1989, 38 (3): 430-438.
doi: 10.7498/aps.38.430
Abstract +
Selection-excited spectra and fluorescence lifetimes of Tb3+ and Ce3+ ions in yttrium gallium garnets are obtained at room temperature. In Y3Ga5O12:Tb, Ce, Tb3+ (donor) emission spectrum and Ce3+( acceptor) excitation spectrum overlaps considerably. The observed fluorescence lifetimes of Tb3+ 5D3 and 5D4 levels decrease with Ce3+ concentration when the sample of Y3Ga5O12: Tb, Ce are excited by UV laser pulse. The mechanisms for nonradiative energy transfer from 5D3 and 5D4 states of Tb3+ to 2D3/2 state of Ce3+ are found to be electric dipole-dipole interaction. The critical distance, rate and efficiency of energy transfer from Tb3+ to Ce3+ ion are obtained. The average critical transfer distance (R0) for 5D3 and 5D4(Tb3+)→2D3/2(Ce3+) are 16.3 ? and 11.2 ?, respectively. Although the energy transfer from the 5D4 state is dominated by dipole-dipole interaction, the dipole-quadrupole interaction must also be considered.
1989, 38 (3): 439-448.
doi: 10.7498/aps.38.439
Abstract +
The four stages of the demagnetization process of oriented sintered Nd-Fe-B alloy after saturation magnetizing along easy direction is studied theoretically in this paper. The results indicate that the nucleation in the soft magnetization regions located at the surface of hard magnetic grains, as well as the irreversible domain wall displacement from the surface to the inside of grains are the dominant factors controlling the intrinsic coercivity of Nd-Fe-B alloy. The rapid reduction of coercivity of Nd-Fe-B alloy with temperature rising are mainly attributed to the thermal movement of atoms it has a harmful effect on the perfection of tetragonal structure in hard magnetic grains and increases the thickness of the soft magnetization transition regions.
1989, 38 (3): 449-457.
doi: 10.7498/aps.38.449
Abstract +
In this paper, we study the regularity that the dispersion equation of MSFVW; in a magnetic anisotropy multilayer structure with finite width varies periodically with the number of magnetic layers increasing. After introducing three self-defined functions, the universal dispersion equation of MSFVW in an arbitrary multilayer magnetic structure is obtained Using similar procedure, a universal dispersion equation of MSBVW in the multilayer struc-ture has also been derived.
1989, 38 (3): 458-465.
doi: 10.7498/aps.38.458
Abstract +
The study on solid electrochemistry of insertion of high-valence cations such as Mg2+, Zn2+ etc. into the layered material such as V2O5, MoS2 is carried out. The insertion compounds are investigated by a lot of physical techniques such as XRD, EMP, ESR. The mechanism of insertion is disscussed.
1989, 38 (3): 466-470.
doi: 10.7498/aps.38.466
Abstract +
A theory of compensating atmospheric turbulence by optical phase conjugation is developed basing on the transmission theory of monochromatic scalar wave through atmosphere and the first Born approximation. It is shown, under the conditions of the nonabsorbing atmosphere and a infinite phase conjugate mirror, that atmospheric turbulence can be corrected thoroughly. Our experiment demonstrated that optical phase conjugate wave generated by SBS can real-time restore the initial optical field.
1989, 38 (3): 471-475.
doi: 10.7498/aps.38.471
Abstract +
The output characteristics of semiconductor lasers under high speed large sinusoidal modulation have been analyzed numerically by means of a system of multilongitudinal-mode rate equations. It is shown that with different modulation parameters, the output may contain a regular pulse series,exhibit spectral widening and spectral shift, and under some adequate modulation conditions, 2-or multi-subharmonic short laser pulse of less than 10 ps may appear, and may be of single mode. A qualitative interpretation is given to some of these phenomena.
1989, 38 (3): 476-480.
doi: 10.7498/aps.38.476
Abstract +
In this paper, the quantum theory of the measurement of the intensity difference between two light beams is analysed. The quantum noise can be reduced by increasing the photon correlation between two beams. For anti-Cauchy-Schwarz light, another type of nonclassical radiation fields, this quantum noise can be reduced to a level below the classical limit. The sub-shot noise may occur in DFWM between the conjugate wave and the transmit wave.
1989, 38 (3): 481-486.
doi: 10.7498/aps.38.481
Abstract +
The Stark spectrum of Ca atom with m = 0 in the vicinity of n = 10 to n = 13 have been obtained by using two-step excitation and photoionization methods in the applied electric field from 0 to 8 kV/cm. The experimental results show that the 3d2 3P0 and 3d2 3P2 valence states are repelled by n= 12 Stark manifold. The interaction among the zero-field non-degenerate states, valence states and Stark states are discussed. The interference phenomenon, in which valence state and Stark states take part, has been observed. The interference is enhanced when the electric field increase.
1989, 38 (3): 487-491.
doi: 10.7498/aps.38.487
Abstract +
We report the method for selecting the high excited states from the complex photoionizing spectra. Thirty energy levels of Sm near the ionization limit have been measured.
1989, 38 (3): 492-496.
doi: 10.7498/aps.38.492
Abstract +
The inverse dielectric function of semiconductor superlattices is derived with inclusion of tunneling effects between adjacent quantum wells. The result is, then, used to evaluate the fast electron energy-loss-spotrum with the conclusion that tunneling effect tend to enhance the energy loss in superlattices.
1989, 38 (3): 497-501.
doi: 10.7498/aps.38.497
Abstract +
In the present article, by using coupling technique, we establish the relation between Ising model and contact process. From this relation, the upper limit of critical temperature of higher dimensional Ising model is obtained. That is, the critical point βc(n) of n-dimensional Ising model must satisfy exp{2βc(n)(2n-1)}·(exp{2βc(n)}-1)≥2/2n-1 and especially, crirical point βc(3) of the three-dimensional Ising model must satisfy βc(3)> 1/2ln1.17.
1989, 38 (3): 502-507.
doi: 10.7498/aps.38.502
Abstract +
The great number of incomplete pseudo-Kossel lines, which can not be avoided and are normally useless in divergent-beam X-ray diffraction, can be used for obtaining the information about interplanar spacings, inclination angles of diffraction planes and the film shifts in multiple exposures with the dual-element radiation method. Therefore, those problems such as the identification of diffraction indices, the determination of crystal orientation and the precise measurement of lattice constants etc. can be solved by the use of diffraction patterns in one experiment.
1989, 38 (3): 508-510.
doi: 10.7498/aps.38.508
Abstract +
Nd-Ba-Cu-O high Tc superconductor is studied with electron diffraction and high resolution electron microscopy. The main phase is orthrombic with distorted perovskite structure. The lattice parameters are a = 3.84?, b = 3.87?, c= 11.7?. There are many defects in the sample. Edge dislocations and anti-phase domains are observed by lattice imaging. The structure mode) of NdBa2Cu3O7-δ is determined from the structure image. Depending on the imaging conditions either the heavy atoms or oxygen atoms appear as white dots in the high resolution electron microscope images. The oxygen atoms can be distinguished from the vacancies in the image under a suitable imaging condition.
1989, 38 (3): 511-515.
doi: 10.7498/aps.38.511
Abstract +
The resistance and thermoelectric power were measured for a series of single phase YBa2 Cu3O7-x samples with different quenching temperature. The relation between the thermopower and temperature indicates that there exists a phonon-drag peak in orthorhombic phase sample. The peak disappears in tetragonal phase sample. This phenomeron suggests that the electron-phonon interaction influences the superconduc tivity of YBa2 Cu3O7-x. According to the experimental data of thermoelectric power, estimation for the Fermi energy and carrier concentration of the sample are made.
1989, 38 (3): 516-522.
doi: 10.7498/aps.38.516
Abstract +
Using image qualification theory of Linfoot, we studied the deforcusing character of imaging of weak phase object in HREM. The power spectrum of electron micrographs of an amorphous carbon thin foil specimen of 10 μm thick is measured from which the distribution of the relative structral content is determined. It is further verified by numerical analysis. The correlation factor, the image fidelity, the choice of the defocus amount in the electron microscope for the unkown crystal objects and automatic focusing is discussed.
