Vol. 37, No. 2 (1988)
1988-01-20
CONTENT
1988, 37 (2): 177-182.
doi: 10.7498/aps.37.177
Abstract +
Numerical results of A1, T2 symmetric sp3 bonded deep level wave function in Si arc calculated in the third neighbors TB frame work, and compared with the existing TB calculations. The influence of different band structure approach on the wave function is given quantitatively.
1988, 37 (2): 183-188.
doi: 10.7498/aps.37.183
Abstract +
Numerical results of A1, T2 Symmetric sp3 bonded deep level wave function in 3c-SiC are obtained Using the Koster-Slater Green's function method developed in reference [1-4]. The wavefunction change with the energy of the defect and occupation probability on 0,1,2,...8 shells around the defect are predicted. The constant of hyperfine structure for 3c-SiC:B are calculated and compared with experimental data.
1988, 37 (2): 189-196.
doi: 10.7498/aps.37.189
Abstract +
In this paper, the optical absorption coefficient, optical gap and the index of refraction of a-Si:H/a-SiNx:H superlattice films were studied as a function of a-Si:H sublayer thickness with a-SiNx:H sublayer thickness being kept constant.
1988, 37 (2): 197-205.
doi: 10.7498/aps.37.197
Abstract +
We report here the far infrared absorption and reflection spectra of the mixed crystals ZnxCd1-xTe with small x in the temperature range of 4.2-300 K and the frequency region of 20-350 cm-1. The local and quasi-local modes induced by Zn and ZnTe in CdTe and the CdTe-like 2TA two-phonon absorption are observed. The frequencies of the modes are estimated by useing the mass-defect model combined with Green's function method. The random element isodisplacement (REI) model is used to calculated the two mode behaviors of the mixed crystals and to best fit the reflection spectra. Besides, the temperature dependence of the phonon absorption and the relaxation factor of CdTe-like and ZnTe-like modes are calculated and explained.
1988, 37 (2): 206-213.
doi: 10.7498/aps.37.206
Abstract +
A spin-polarized version of the tight-binding Green's function scheme is developed for GaAs:Cr2+(3d4) system, which is under hydrostatic pressure and is alloyed with AlAs in different concentration. Results on the variation trends of 5E excited and 5T2 ground acceptor levels of GaAs:Cr2+ with different pressures and aluminum concentrations are reported. The theory shows that under certain pressure and Al concentration the 5E state will shift into the band gap from the bottom of conduction band. The 5E→5T2 luminescence which can not be observed in normal condition will appear in such case. Good overall agreement between theory and experiment is found. The theory also predicts that the similar luminescence process-would occur when GaAs is alloyed with Gap in certain concentration, but this still waits for experimental verification.
1988, 37 (2): 214-220.
doi: 10.7498/aps.37.214
Abstract +
The dispersion curves of phonons along three crystallographic axes for isomorphous crystals NaBrO3 and NaClO3 have been measured by using coherent inelastic neutron scattering. The velocities of elastic waves along these directions and three independently elestic constants C11,C12 and C44 are deduced from the dispersion curves in the region of small wave vectars. The experimental results verified directly the prediction of portigal's theory that the velocities of left circularly polarized phonons and the right polarized ones distribute on both side of a particular average velocity v(TD) symmetrically, the value of v(TD) can be determined uniquely by the velocities on other directions or the zero-order approximative elastic constants.
1988, 37 (2): 221-228.
doi: 10.7498/aps.37.221
Abstract +
In the investigation of sound interaction between two rectangular plane waves, a deduction has been made by Westervelt that there is no sound scattering by sound outside the region of interaction. However, it seems to be little significance to say that "outside the common region", since its volume is practically infinite. In this paper, the interaction between a cw plane wave and a plane pulse travelling with sound speed is considered. Both of them satisfy the homogeneous wave equation. Outside the common volume they can be employed to study the sound scattering by sound. It is shown in this paper that there is no scattering which follows the law of causality. It is also shown that it appears to be not appropriate to apply Li-ghthill's farfield integral for calculating sound scattering by sound in this case.
1988, 37 (2): 229-238.
doi: 10.7498/aps.37.229
Abstract +
The "hard" pulse sequences with spin echo for one dimensional homonuclear correlation editing (1 D HCE) are discussed with density operator theory. The experimental results coincides with the theoretical expectation. It is shown that the correlation obtained from I D HCE spectra is similar to that from COSY. The advantages of this technique are: 1) saving time, 2) saving computor memory, 3) keeping the sensitivity, resolution and the fine structure of 1 D NMR spectra.
1988, 37 (2): 239-247.
doi: 10.7498/aps.37.239
Abstract +
The numerical solution of the Eliashberg equation is analysed by a graphic analytic method, and the following conclusions are arrived. The superconducting Tc of a superconductor can be enhanced through the ‘hardening' of its normalized effective phonon spectrum g(ω). And the ‘softening' of g(ω) could enhance the Tc for a superconducting material with small λ, but not for the superconductor whose A is large.
1988, 37 (2): 248-253.
doi: 10.7498/aps.37.248
Abstract +
The electrical resistivity and magnetoresistance of amorphous Cu33Y67 alloy has been measured. The alloy was prepared by melt-spinning in He gas. Interaction effect can provide a good quantitative explanation for the temperature depen-dence of the electrical resistivity at low temperatures with a main contribution of the form of T1/2 below 4.5 K. Its variation at higher temperatures can also be explained by a combination of interaction and weak localization effects. The magnetoresistance measurements up to 1.8 Tesla reveals predominant localization effects with a strong influence of the spin-orbit scattering. The data are rather larger than that predicted by weak localization. An overall good fit is obtained if one increases the theoretically predicted strength of localization by 3 times. One fitting parameter, spin-orbit scattering time τ50, is unchanged, while inelastic scattering time τi's used fitting to two set of the data of resistivity and magnetoresistance are close to each other.
1988, 37 (2): 254-260.
doi: 10.7498/aps.37.254
Abstract +
Up to now, almost all many-body theoretical calculations on the ground state of atoms took the Hartree-Fock (HF) model as zeroth order approximation. In this paper, zeroth order Hamiltonian is taken to be Hartree-Fock-Slater (HFS) type, in the double excitation approximation, many-body calculation on the ground state exchangecorrelation energy of beryllium atom is made, the result is in good agreement with experiments and other many-body theoretical calculations, which take HF model as zeroth order approximation. Our calculation shows that, take the HFS model as zeroth order approximation instead, successful many-body calculation on the ground state property of closed shell atoms can also be made.
1988, 37 (2): 261-267.
doi: 10.7498/aps.37.261
Abstract +
There is some trouble in experimental study of optical transformation developing from low- to high-sequence. In this paper, to solve these problems, a five-plane coherent system is proposed. As an example, a three-plane and a five-plane experimental systems have been established to realize the 1-dimensional 32-sequence Walsh transformation. The experimental results are in agreement with the theoretical expectations.
1988, 37 (2): 268-273.
doi: 10.7498/aps.37.268
Abstract +
We have observed very regular diffraction patterns on the screen behind the crystal when focusing He-Ne laser beam illuminates the thin sample along X or Y axis of the LiNbO3:Fe crystal. This is utterly diffent from photoinduotd light scattering phenomenon which arises from phase-noise-gratings produced by optical-induced refractive index change in the crystal, it had been observed long ago. This self-diffraction pattern can be explained by selfdiffrac-tion theory and complicated lens-like effect formed in the crystal when focusing laser beam illuminates it. These diffraction patterns can show the feature of optical-induced refractive index change in the crystal clearly, and the maximum of optical-induced refractive index change △n can be calculated directly from the number of diffraction ring. Furthermore, we have also studied and discussed the conditions of formation of laser-induced self-diffraction and its competition behavior with photo-induced light scattering.
1988, 37 (2): 274-282.
doi: 10.7498/aps.37.274
Abstract +
In order to solve the problems on calculation of attachment energy Eatt of ionic crystals with complicated structures, several formulas derived according to the principle of PBC (Periodic Bond Chain) theory is presented. The appropriate computing programme has been worked out. The morphology of KTiOPO4 was deduced from the structure. The categories of the crystals faces have been distinguished by means of PBC theory. It was found that {100}, {011} are F-forms, and {210}, {010} are more important S-forms. The form of {001} is found to be K face. The calculation of Eatt for each form has been carried out, and it gives the relative importance of these faces. The results are in satisfactory agreement with observations. The calculating formulas and the programs can be used directly for calculating Eatt of other crystals belong to cubic, tetragonal and orthorhombic systems.
1988, 37 (2): 283-294.
doi: 10.7498/aps.37.283
Abstract +
Using the static simulation method, the variations of local structure (Voronoi polyhedra statistics) and atomic-level stress in a model of amorphous iron under pressure are examined in this paper. The results show that external pressure increases the local stress and energy on each atom in the system, extends their distribution range of values and enhances the extent of fluctuation, though a homogenization of Voronoi polyhedra is promoted by the same procedure. The calculation shows that the local stresses in the structure studied divided into compressed and expansed regions, embeded each other with some percolative character. The compressed region which covers about 50 per cent atoms of the system at normal pressure and plays a role of rigid framwork of the body, will grow on increasing pressure at the expense of cosuming the expanded region. It is suggested that as the oppositely stressed regions are essentially in distinct physical conditions, they are expected to show different behaviours and give different contributions in a thermo-activated transport process. For this reason, it would be more reasonable to treat a metglas as an inhomogeneous medium on analyzing its structural relaxation mechanisms.
BRIEF REPORT
1988, 37 (2): 295-300.
doi: 10.7498/aps.37.295
Abstract +
The bifurcations, chaos and intermittency in the f-biased Josephson junction are investigated by numerically integrating the equation for Stewart-McCumber model with an interference "∈ cosφ" terra. In addition, the relation between low frequency noise and the routes to chaos in Josephson junctions is discussed.
1988, 37 (2): 301-304.
doi: 10.7498/aps.37.301
Abstract +
The process of the lattice damage and its development in the Hg1-xCdxTe crystal under electron irradiation with high dose and high energy have been studied at lattice level by high resolution electron microscopies. The results indicate that Hg1-x CdxTe lattice damage was caused by the deformation of the [(Hg, Cd)Te4] tetrahedra due to the strong electron irradiation. These deformations could be seen on the {111} plane and they developed along the {111} plane as steps. Moreover, a new superlattice with larger parameter of unit-cell was observed along the [110] direction.
1988, 37 (2): 305-310.
doi: 10.7498/aps.37.305
Abstract +
Carbon and oxygen on the Mo(l00) and Mo(l1l) surfaces can not be removed by bombarding the sample with argon ions at the ambient temperature. While carbon and oxygen can be reduced by bombarding the sample using nitrogen ions with primary energy of 1 keV and beam current of 6 μA for 10-15 min. This may be due to the adsorption of nitrogen reached saturation. After heating sample to 400-600℃ carbon and oxygen disappeared; at 600-650℃, Auger peak of nitrogen dropped suddenly and then decreased gradually with increasing temperature, carbon segregated simultaneously on the surface. Complete desorption of nitrogen took place at 730℃ and 775℃, A p(2×2)-C and a c(6×2)-C LEED patterns were observed respectively. After nitrogen desorbtion, the sample is cooled to room temperature, oxygen segregated on Mo(lll) surface. Repeated heating to above 650℃, carbon disappeared from the surface, nitrogen and oxygen appeared on the surface, until at 800℃ nitrogen and oxygen disappeared completely and a clean surface Mo(lll) LEED pattern was obtained. Then cooling the sample to room temperature, oxygen segregated on surface again. After bombarding the Mo(lll) surface with argon ions, carbon and nitrogen agan appeared on the surface. Heating to 700℃ and 760℃ oxygen and nitrogen disappeared and a p(6×6)-C LEED pattern was obtained.
1988, 37 (2): 311-317.
doi: 10.7498/aps.37.311
Abstract +
Two surface superstructures (4×1)-O and (2×2)-S, induced respectively by oxygen and sulphur segregation on the V(001) surface, are studied in detail by ARVPS. The energy levels and symmetry of the adsorbate surface states derived from S- and O-ordered adsorbate over-layers are determined. Experimental evidence shows that the adsorption sites of oxygen on V(001) surface are four-fold hollow sites. All the experimental results consist with theoretical calculations, and are similar to that for oxygen on Ni(001) and Cr(001) surfaces.
1988, 37 (2): 318-322.
doi: 10.7498/aps.37.318
Abstract +
In this paper, the crystallographic and magnetic structures of intermetallic compound Pr2(Fe0.8Co0.2)14B studied by neutron powder diffraction are reported. This compound crystallize in Nd2Fe14B type tetragonal structure, a = 8.8110?, c = 12.2307?. Assumming ferromagnetic spin configuration and easy magnetization along c axis and equal magnetic moment for Fe and Co atom on the same site, profile refinement of the measured neutron diffraction data gives the magnetic moments on two non-equivalent Pr sites Pr4f and Pr4g as 1.2 and 1.4 μB, and moments on six non-equivalent transition metal ion sites T16k1 T16k2, T8j1, T8j2, T4e, and T4c as 2.2, 2.1, 1.9, 3.1, 1.6 and 1.0 μB. Substituted Co atoms are distributed randomly among six non-equivalent sites, no preferred site occupation was observed.
1988, 37 (2): 323-329.
doi: 10.7498/aps.37.323
Abstract +
The diffraction losses and phase-shifts of TEMpl modes in optical resonators are calculated by quasi-geometric approximation and by the matrix theory (a strict diffraction theory), and the values obtained from the two methods are compared and studied. We come to the following conclusions: (I) The relation of the diffraction losses with the phaseshifts differences between the values obtained from the two methods are close to exponential. (II) When the diffraction losses≥20%, the frequency degeneracy of TEMpl modes may be destroyed in a marked manner, and this would lead to the split of resonant frequency. (III) The exact diffraction loss values calculated from the strict method are nearly linear with the loss values calculated from the approximation method, its slope is b = 0.3559. When the Fresnel number of resonator ?> 2, all the conclusions are independent of mode numbers l, p, and Fresnel number ?. The above mentioned conclusions are obtained only for characteristics of transverse modes, whose losses≤99%, in axial-symmetric stable resonators G2 = G2= 0.5.
1988, 37 (2): 330-334.
doi: 10.7498/aps.37.330
Abstract +
A single-mode dynamical equation is obtained from the Maxwell equation with the slowly varying amplitude approximation and the boundary conditions of the cavity, here the mean field limir and the good quality cavity case have been used. This equation is useful in describing the dynamical behavior of intrinsic optical bistable systems and/or lasers with injected sig-nals for any kinds of materials including two-level atoms. Furthermore, according to the li-near stability analysis, a generalized instability criterion is derived.
1988, 37 (2): 335-340.
doi: 10.7498/aps.37.335
Abstract +
A new mode-locked equation suitable for synchronously pumped dye lasers is presented, after the drawbacks in the conventional equation are pointed out. The analytical expressions for pulsewidth τ and pulse-intensity l0 are obtained by expanding the gain G(t) to second order of t only. The theoretical analyses are well consistent with experiments and can interpret some experimental phenomena which can not be explained by the second order solution of the original equation.
1988, 37 (2): 341-346.
doi: 10.7498/aps.37.341
Abstract +
Solid-solid surface adsorption of Eu2O3 on η-Al2O3 and SiO2 gel has been investigated using M?ssbauer spectroscopy and X-ray diffraction analysis. The results suggest that after appropriate treatment Eu2O3 disperses spontaneously onto the surface of both supporter materials. No indications of remaining crystalline Eu2O3 have been found below the limiting mono-layer concentration. In the case of η-Al2O3, it is suggested that below the limiting monolayer capacity Eu2O3 covers the surface in a disordered monolayer configuration. For higher Eu2O3 contents a second layer starts to appear with a structure similar to that of the bulk crystalline phase. In the case of SiO2 gel, it is suggested that the monolayer as well as the second layer configuration of Eu2O3 is highly disordered. It seems that the M?ssbauer parameters, isomer shift and linewidth allow additional insight into the surface layer structures formed by solid-solid adsorption.
1988, 37 (2): 347-352.
doi: 10.7498/aps.37.347
Abstract +
We have discussed SU(N) chiral grand unified preon models under some constraints assumed in the paper And we have constructed SU(10) chiral grand unified preon model in detail. Five families exist without exotics.
