Vol. 38, No. 6 (1989)
1989-03-20
CONTENT
1989, 38 (6): 873-878.
doi: 10.7498/aps.38.873
Abstract +
In this article, a nonlinear wave equation of bounded acoustic beam in relaxating media is presented and a general solution of higher harmonics resulting from the nonlinear distortion of propagation is found by using the pertubation approach. Investigation shows that for the Gaussian ultrasonic field, the solution of higher harmonics can be given analytically, moreover their corresponding radical distributions of amplitude always maintain the Gaussian profiles. Although the dispersion may affect the amplitude of various harmonics, the variation of phase velocity of those keep the same law as the small amplitude waves of corresponding frequencies do.We also show that by means of Blackstock' operator the obtained results can be applied te the case of media with arbitrary dissipation and dispersion, including some biomedia in which the relationship between the absorption and frequency may be obtained only empirically.
1989, 38 (6): 879-890.
doi: 10.7498/aps.38.879
Abstract +
The interaction potential with the form as V(x)= x2+λx2/(1+gx2) where g >0, appears in several areas of laser theory, quantum field theory, atom and nuclear physics. One could consider that the solution of the eigenequation either by the classical Rayleigh-Schr?dinger perturbation scheme or by the perturbed ladder operators scheme. Nevertheless, the perturbation series does not converge for any values of λ and g. In the present paper, it is shown that this difficulty can be overcome as long as the potential function can be expanded in a convergent series on the basis ofthe Hermite polynomials. Therefore, the eigenequation ((d2)/(dx2)-V(x)+ξ)φ(x)=0,∞2)/(dX2)-b2X2-Σkc2kH2k(b1/2X)+ξ)φ(X)=0.
1989, 38 (6): 891-899.
doi: 10.7498/aps.38.891
Abstract +
Using the perturbation method to study the influence of the coupling between occupied states and empty states on the electronic band energy, we obtained analytical expressions for semiconductor force constant calculation within the scheme of extended band orbital approximation. The surface phonon dispersion curves and related vibrational amplititude distribution of Si(111) ideal, 1×1 relaxed and 2×1 reconstructed Haneman model surfaces are calculated by means of these expressions. The results for different surfaces show the important effects of surface relaxation and reconstruction on the properties of surface phonons. It is also shown that the Haneman model for Si(111)-2×1 reconstructed surface can not explain the experimental surface phonon measurement very well.
1989, 38 (6): 900-906.
doi: 10.7498/aps.38.900
Abstract +
The Embedded Atom Method is applied to study the properties of surface phonons of transition metal Cu. We derive the formula of surface lattice dynamical matrix from the se-miempirical functions. As an example, we calculate the surface phonon dispersions on Cu (100) surface; the calculated Raileigh phonon dispersion curve on Cu(100) along the direction ΓX is compared with that measured by electon-energy-loss-spectroscopy, and satifactory agreement is obtained.
1989, 38 (6): 907-913.
doi: 10.7498/aps.38.907
Abstract +
The deep energy levels and the wavefunctions of V3- in silicon are calculated by using the Koster-Slater Green's function method. Numerical results show that there are five energy levels in the energy gap, i.e., E(A2)=0.417eV, E(B1)=0.492eV, E(B21)=0.512ev, E(A1)=0.532eV, E(B22)=0.608eV. The hyperfine interactions (h.f.) constant associated with these states are calculated. According to the comparison of the theoretical h.f. constant with the experiments, we determine that the B1-state is occupied by the unpaired electron of V3-. The distributed probability of V3- in B1-state on the nearest neighbour atoms is about 60.2%, the major part of which is centered on the two atoms in the plane determined by the trivacancy.
1989, 38 (6): 914-922.
doi: 10.7498/aps.38.914
Abstract +
For two main Jahn-Teller distortion modes of the divacancy in Si, hyperfine interactions of the unpaired electron of both negative and positive charged states (V2-,V2+) are calculated by using extended Koster-Slater model. The calculated results in agreement with the experiments are obtained., From these, we determe that the unpaired electron of V2+ is located at the symmetric state Ag of the energy level at 0.3eV and the V2- is located at the symmetric state Bu of the energy level at 0.63eV. We infer that the EG1 mode is the preferential mode of distortion for both V2- and V2+.
1989, 38 (6): 923-930.
doi: 10.7498/aps.38.923
Abstract +
Based on the molecular-orbital theory, the secular equation of molecule consisted of two different atoms can be deduced. Solving the above equation, the quantitative expression of the characteristic constant N and λ for the linearly combined wave function of the compound and the equation of the bond forming energy or the anti-bond forming energy are obtained. Using the difference between this two energies, the N and λ can be related to the average energy gap Eh arised from the symmetric potential Vcov, the energy gap C arised from the anti-symmetric potential Vion and the total energy gap Eg, hence, the dependence of λ on the fraction of the spectrum ionicity fi and the ratio C/Eh are deduced. From the dependence of λ on fi, the expression connecting fi and the deviation coefficient γ for the electronic stopping power of the compound may be obtained. According to the above equations and considering the structural characteristic of zincblen-de and wartzite structure, the reason which causes the difference of the deviation coefficient γ and the piezoelectric constant epol between the two structures can be well explained. The same turning point can be found in all the three curves expressing the dependence of C/Eh, γ and epol on fi respectively, hence, we could see that the bond and structural property of crystal will be the most essential cause which results in the change of chemical and physical property of semiconductor compound.
1989, 38 (6): 931-937.
doi: 10.7498/aps.38.931
Abstract +
The structure, structural relaxation and crystallization of metallic glass Zr78Co22 are investigated by the small angle X-ray diffraction, the wide angle X-ray diffraction and the field ion microscopy, together with the measurements of the superconducting critical temperature and the microhardness. The results indicate that there exists obviously the amorphous phase separation in the as-quenched state of the metallic glass Zr78Co22. The compositions of two segregated amorphous phases are similar to pure Zr and Zr4Co respectively. In the process of structural relaxation, the changes of the toplogical short range order are essential and controlled by the nucleation-growth mechanism. When the number of nucleation is sufficient, the segregation grow homogenously and identically.
1989, 38 (6): 938-946.
doi: 10.7498/aps.38.938
Abstract +
In the case of existence of an applied magnetic field, the movement of the ring-shape quasi-fluxons in the circular symmetric annular Josephson junctions is investigated numerically. The behavoir of the quasi-fluxons in an applied field depends upon the geometric size of the junctions. If the width of the annular junctions is 5λJ in the radial direction, the life time of the quasi-fluxon is increased by applied field. If the width of the annular junction is 10λJ, the life dme of the quasi-fluxon is increased as well, and in addition, some evident changes of the behavior of the quasi-fluxons occur in the process of propagation and in the reflection at the boundary, due to the applied field. The size of the first zero-field step increases with applied field in the lower current direction. These changes are caused by an inhomo-geous distribution of the applied field in the junctions. A tunable resonator in the gigahertz-range using quasi-fluxons on a lossy large-area annular Josephson junction is also proposed in this paper.
1989, 38 (6): 947-955.
doi: 10.7498/aps.38.947
Abstract +
In this paper, the geometry size effects of the ringshape quasi-soliton solutions in the perturbed Sine-Gordon equations (SGE) in the circular symmetric annular Josephson junction are investigated with numerical method. The perturbed SGE, when the inner radius r0 of the circular symmetric annular junctions is larger then or equal to 7.5λJ, there exists a kind of ring-shape quasi-soliton solutions, which correspond to the quasi-fluxon of excitation in the circular symmetric annular Josephson junction, and the first zero-field step also. The range of the first zero-field step depend strongly on the size of the inner radius r0 and widths (αr0-r0) of the circular symmetric annular junctions, but the geometry size effects of the nature of the ring-shape quasi-solitons are more complicated.
1989, 38 (6): 956-964.
doi: 10.7498/aps.38.956
Abstract +
We point out in this paper that the heavy Fermion system is a kind of Kondo system whose localized f-electrons can change with temperature. The theory suggests the existence of spontaneous magnetic moment in particular temperature range. According to the different distance between the f-electron band and Fermi level, there are different types of spontaneous magnetic moment effect. We also point out that the anomaly in specific heat versus temperature-curve is caused by the change of number of f-electron in heavy Fermion system. The theoretical values of specific heat coincide well with six experimental data.
1989, 38 (6): 965-972.
doi: 10.7498/aps.38.965
Abstract +
Molecular fluorescence spectra of dye adsorbed on silver colliod and silver mirror were studied. Acriding Orange was used as sample in the experiment. We have found that the enhancement or quenching are depend on the competition of two processes, i.e., local field enhancement and non-radiation energy transfer from the molecule to metal surface. The fluorescence is enhanced when enhanced absorption and enhanced emission conditions are achieved. However, molecular fluorescence is far less enhanced then Raman. Theoretical calculation shows that peak enhencement of fluorescence intensity will be 10-102. It agrees with the experimental value for Acriding Orenge adsorbed on silver mirror.
1989, 38 (6): 973-980.
doi: 10.7498/aps.38.973
Abstract +
The semi-plane-symmetric static general solution generated by semi-plane-symmetric non-null electromagnetic fields is obtained. We prove that there are only three Killing vector fields ?/?x, ?/?y and ?/?t in this kind of space-times. The space-time singularity is also investigated. It is shown that all these space-times are geodesically incomplete, and all incomplete geodesies correspond to scalar polynomial curvature singularities.
1989, 38 (6): 981-986.
doi: 10.7498/aps.38.981
Abstract +
The crystalization process of Si-W alloy film and the change of interfaces of Si-W poly-Si/SiO2/Si(100) after annealing have been studied by cross-sectioned TEM method. After annealing at above 440℃, nucleation of crystalline WSi is uniform in the alloy film, i.e., there is no preferential nucleation at the surface and interface. When the annealing semperature is lower than 800℃, the crystallization reaction take place in the alloy film, surface and interface of alloy film remain almost unchanged. After annealing at 800-1000℃, small thermal grooves appear on the surface of WSi. Very small fluctuation appears at the poly-Si/SiO2 interface as observed by using high resolution electron microscopy, but WSi/Si interface becomes quite rough. We propose that interdiffusion of Si and W atoms. in the interface driven by the interface tension is the cause of interface roughness. The interdiffusion of Si and O atoms is difficult due to the strong Si-O bond in SiO2, so the Si/SiO2 interface keeps nearly flat.
1989, 38 (6): 987-990.
doi: 10.7498/aps.38.987
Abstract +
XPS from Ce3d level of eerie ammonium sulfate, eerie sulfate, ceric-benzilic acid complex, eeric iodate, cerie peroxide and cerie dioxide were recorded. All of the spectra exhibit two distinct sets of structure corresponding to trivalent and tetravalent cerium ions. The Ce3d XPS of cerous oxalate, cerous sulfate, cerousbenzilic acid complex, cerous iodate and cerous chlorite were also recorded. All of them only show one set of spin-orbit splitting structure with shake-down satellites at lower binding energy side of the main peaks. The Ols spectrum of CeO2 after heating in vacuum shows two peaks with an energy separation of 2.5eV, which reflects that the valence fluctuation Ce(4f0)O(2pπ)←→Ce(4f1)O(2pn+1) may be responsible for the mixed valency in these nominal tetravalent cerium compounds.
1989, 38 (6): 991-994.
doi: 10.7498/aps.38.991
Abstract +
This paper deals with X-ray diffraction profile analysis for the sample with a micro-strain gradient in its surface layer. On the assumption that the variation of micro-strain L2> with depth t is expressed as L2>-Σam(L)tm, Warren-Averbach method is modified so that it can be used in this case. For the special case of L2>=α0+a1(L)t, the relationship between the micro-strain L2> and the depth t can be determined by analyses of diffraction profiles belonging to two different radiations.
1989, 38 (6): 995-997.
doi: 10.7498/aps.38.995
Abstract +
The dispersed molten droplets of Pd40.5Ni40.5P19 alloy solidified during fall down in a 1.2 m drop-tube which is filled with purified helium at 0.8 atmosphere. Owing to solidificat ion without container occurring at high undercooling, the heterogeneous nucleation was inhibited and the metallic glass sphere of 2 mm in diameter was obtained, which is the largest one prepared by dropping tube up to now.
1989, 38 (6): 998-1004.
doi: 10.7498/aps.38.998
Abstract +
According to the model of regular dodecahedron and combining geometric projection with crystal diffraction, electron diffraction patterns, of icosahedral phase in Al-Mn alloy with twofold, threefold and fivefold axes have been indexed using three dimension indexes. Some significant primary results have been obtained.
1989, 38 (6): 1005-1011.
doi: 10.7498/aps.38.1005
Abstract +
A phenomenological model of Bose elementary excitations is proposed to explain the anomalous thermal properties of glasses at low temperatures (<1 K), namely, the nonlinear temperature dependence of the specific heat, the temperature In T law of the sound velocity. Wealso predict a negative thermal expansion between 0-1 K.
1989, 38 (6): 1012-1015.
doi: 10.7498/aps.38.1012
Abstract +
The correlation function of two dimensional electron gas with the presence of a strong perpendicular magnetic field has been studied on the basis of the wave function in small system. A formula of the correlation function of a finite cluster has been obtained for numerical calculation.
1989, 38 (6): 1016-1020.
doi: 10.7498/aps.38.1016
Abstract +
In this paper, we report the time dependence of the magnetic field inside a YBa2Cu3O7 tube, when switching on a field He outside the tube after a zero field cooling the tube into a superconducting state. In our experiment He is smaller than 4Hrm, where Hrm is the trapped field of the tube. The dependence can be expressed as Hi(t)=H0 + B0(Int + 1-exp(-t/τ)), where H0, B0 and 1/τ are functions of He, and they keep rising when He>Hrm. We suggest that the term of Int is caused by flux lines creeping, while (1-exp(-t/τ)) results from flux lines fluctuating, which is a short time effect. The shielding effect of YBa2Cu3O7 tubes is perfect for low dc field (rm/2), and better than the best normal metal for ac magnetic noise.
1989, 38 (6): 1021-1025.
doi: 10.7498/aps.38.1021
Abstract +
Single phase samples of PrBa2Cu3O7-δ with orthorhombic structure were prepared by solid State reaction method. Resistance measurement was performed by a standard dc four-probe technique. It is found that the resistance exhibits semiconductor-like behavior. Results of XPS measurement indicate obviously the existence of Pr4+ in PrBa2Cu3O7-δ. Finally, the band structure was used to discuss the reasor why PrBa2Cu3O7-δ does not show superconductivity.
1989, 38 (6): 1026-1029.
doi: 10.7498/aps.38.1026
Abstract +
The relationship of the structure and superconductivity in the system Bi,PbCa3Sr3Cu4Oy and Bi4Ca3sr3Cu4Oy is investigated. It is found that both systems belong to the material with 4334 phase identically but they have different superconductivity. The reason causing this difference may be the subtle variation coming from the arragement of atoms, the number and dis-tribution of oxygen deficiency and the feature of electrons within the cell.
1989, 38 (6): 1036-1040.
doi: 10.7498/aps.38.1036
Abstract +
The far IR spectra and the photoconductivity of the proton-exchange LiNbO3 waveguide were measured. Experimental results show that the machanism of good photorefractive damage resistance of protonexchange LiNbO3 waveguide is related to the fact that its photoconductivity is 5-10 times higher than that of pure LiNbO3 crystal.
1989, 38 (6): 010300.
doi: 10.7498/aps.38.10300
Abstract +
We proposed a new method to study adsorption dynamics by surface enhanced Raman scattering (SERS). A simple theortical model of adsoption dynamics for solid-liquid interfaces was established. We analysed the time dependence of SERS intensity and further deduced the parameter of adsorption dynamics, such as constant of adsorption speed, adsorption activation energy. As an example, we studied the adsorption dynamics of P-amino-benzoic acid adsorped on the silver colloid. The results show that the faster process of the time dependence of SERS are related to the adsorption process. From the experimental data and our theoretical model, the constant of adsorption speed were deduced. We believe that the study of adsorption dynamics by SERS is very promising.
