Vol. 36, No. 10 (1987)
1987-05-20
BRIEF REPORT
1987, 36 (10): 142-144.
doi: 10.7498/aps.36.142
Abstract +
We study the 2-D electron system in a strong magnetic field with the contribution from the meutralizing backgound included. We find that the downward cusp of the ground state energy only occurs for several angular momenta.
1987, 36 (10): 1321-1329.
doi: 10.7498/aps.36.1321
Abstract +
By computer simulation, the pressure induced variation in the behavior of amorphous metals is investigated. We used the Lennard-Jones potential, which is fitted with the equation of state of iron, to relax the amorphous model constructed by sequentially stacking the hard sphere together with energy minimization consideration, so as to yield an amorphous iron model containing 1067 atoms with periodic boundary. The variation of RDF of this amorphous iron model under the application of high pressure is also examined. From the obscuring tendency of two splitted sub-peaks in the second maximum of the RDF of the pressurized model, we suggest that the local ordered correlation in the amorphous alloys might be destroyed during compression. The P-V relation of amorphous iron has also been estimated by comparing with the crystalline state.
1987, 36 (10): 1330-1335.
doi: 10.7498/aps.36.1330
Abstract +
The wavefunctions of the A1 and E states of the ideal divacancy in GaAs, GaP are calculated using the basic equations given in ref. [1] and the tight-binding Hamiltonian given by P. Vogl et al. It is shown that the largest part of the wavefunctions of divacancy states is on the three nearest Ga atoms of the As or P vacancy, the rest part of the wavefunction decreases slowly and non-monotonically as the distance from the defect increases.
1987, 36 (10): 1336-1343.
doi: 10.7498/aps.36.1336
Abstract +
By using of the nonlinear luminescence correlation technique, a new time resolved optical spectroscopy technique has been developed and applied to investigating of hot carrier relaxation processes in GaAs-GaAlAs multiple quantum well structures. It has been found that the well width has a significant effect on the relaxation processes. For a sample with Lz=40?, the time constant of the LO-phonon relaxation was found to be as long as 40ps. The physical me-chanism of this weakened electron-phonon interaction is also discussed.
1987, 36 (10): 1344-1348.
doi: 10.7498/aps.36.1344
Abstract +
In this paper, on the basis of a single-particle model, the relationship between spontaneous radiation and stimulated radiation in Cerenkov free electron lasers is obtained. The results show that in Cerenkov free electron lasers there is a relationship similar to Madey Theorem in wiggler free electron lasers. The gain calculation of oblique angle stimulated Cerenkov radiation by making use of this relationship is given.
1987, 36 (10): 1349-1354.
doi: 10.7498/aps.36.1349
Abstract +
The radial distribution function of hydrogenated metallic glass Ni24.3Zr75.7H0.65 was deter-mined with X-ray scattering technique to investigate the influence of hydrogcnation on the structure of metallic glass Ni24.3Zr75.7 and the local surroundings of hydrogen atoms in the struc-ture of metallic glass Ni24.3Zr75.7H0.65.
1987, 36 (10): 1355-1358.
doi: 10.7498/aps.36.1355
Abstract +
There were three different versions on the space group of β-LaNi5·Hx(x～6) based on the neutron diffrection measurements: P31 m, P321 and P6/mmm. The arguments were investigated by a synthetical study which combinated the proton NMR second moment and the confi-gurational entropy analyses. The statement involved: to make clear a concept of the rigid repel-lence correlation radius rc; to deduce the corelation coefficient taples for P31 m, P321 and P6/ mmm at different rc's; to propose possible statistical assumptions based on the occupation numbers provided by the neutron diffrections; to modify the formula for calculating the configura-tional entropy and to contrast the calculated values with the experimental value of configuration-al entropy; to contrast the NMR second moment calculated under the same statistical assumption with the value of the NMR experiment; to select out a appropriate version which is capable to fit all the experimental facts. Having conducted such a synthetical study, the conclusion is that the space group of β-LaNi5·H6 should be P6/mmm.
1987, 36 (10): 1359-1363.
doi: 10.7498/aps.36.1359
Abstract +
EXAFS spectra (including near edge X-ray absorption spectra) have been measured at the Mn K edge of i-Al6Mn, i-Al4Mn and crystalline Al6Mn. The first near-neighbor structures about Mn atom of the i-Al6Mn and i-Al4Mn have been studied and discussed. We found that the average distance between Al and Mn atoms is about 2.52 angstrom in quasicrystalline phases and its shorter than that in crystalline Al6Mn. The coordination number around Mn atom is about 5 in quasicrystalline phases and is less than that in crystalline Al6Mn. The structure unit may be the same as in i-Al6Mn and i-Al4Mn. It is reasonable that the Mn atoms distribute on the surface of the unit.
1987, 36 (10): 1364-1370.
doi: 10.7498/aps.36.1364
Abstract +
An investigation is made on the structure and magnetic properties of the tetragonal phase Nd2Fe14 B as influenced by addition of Si. The results show that: Si (up to a content of as much as twice that of B) does not destroy the tetragonal structure of Nd2Fe14B, but forms a pseudo-ternary intermetallic compound Nd2(Fe, Si)14B. The lattice constants and saturation magnetization of Nd2 (Fe, Si)14-B decrease and its Curie temperature increases with increasing Si content. The magnitude of the anisotropy field and the easy direction of magnetization of Nd2Fe14B at room temperature are not affected by the addition of Si. The inclusion of Si in Nd2Fe14B has a great influence on the magnetic anisotropy of Nd2Fe14B at low temperatures, showing an increase in the angle between c-axis and the direction of easy cone.
1987, 36 (10): 1371-1374.
doi: 10.7498/aps.36.1371
Abstract +
Amorphous thin films of PrxCo1-x alloys were prepared over the composition range 0.06-0.86 by the vacuum evaporation method with two sources. The magnetic properties of those films were measured by using extracting sample magnetometer, vibrating sample magnetometer and the alternating susceptibility set. The dependence of magnetization of these films on temperature and field were studied. It was found that the magnetization has a sudden drop near the temperature corresponding to the maximun of the value of the alternating magnetic susceptibility, and for samples with xco and Pr atom μpr were calculated. The effective magnetic moment of Co atom μco equals l.36f(x), where f(x) is the probability for bearing magnetic moment of cobalt atoms. The effective magnetic moment of Pr atom equals 1.6 μB in. the composition range 0-40% and decreases rapidly in the range 0.4-0.86.
1987, 36 (10): 1375-1381.
doi: 10.7498/aps.36.1375
Abstract +
The early oxidation process of pure Fe was studied by XPS, UPS and AES. When the temperature and partial pressure of oxygen is not too high, the product of the reaction between polycrystalline Fe and oxygen is pure Fe3O4, but not FeO or a-Fe2O3 or a structure of layers of the three compounds. If the temperature is higher than 600℃ and the partial pressure of oxygen approach 1 × 10-6 Torr, the thermo-desorption process occurs instead of oxidation process on polystalline Fe surface.
1987, 36 (10): 1382-1385.
doi: 10.7498/aps.36.1382
Abstract +
The Laser induced fluorescence spectra and excitation decay process of Ni2+ doped with chrysoberyl were studied in temperature rang of 10 K to 300 K. It was shown that the intrinsic radiative lifetime of 3T2g state is 123±7.2 μs. Mott activation energy is 1147 cm-1. Ni2+:BeAl2O4 Crystal has considerable high radiative rate and luminescence efficiency at room temperature and is a possible good candidate for making tunable laser.
CONTENT
1987, 36 (10): 1241-1246.
doi: 10.7498/aps.36.1241
Abstract +
With the local approximation near the rational surfaces, the analytical expressions of the evolution of non-linear tearing modes are derived from MHD equations; and are compared with the previous results for linear and non-linear tearing modes. The phenomenon of modulation and anomalous increase is explained, which was found in the experiments of the maor disruptions in Tokamaks.
1987, 36 (10): 1247-1254.
doi: 10.7498/aps.36.1247
Abstract +
A theory is presented for designing broadband composite pulses in solids by using perturbation method of quantum mechanics combining with coherent averaging theory. A broadband composite π pules Px(90°)Py(90°)Px(90°) is designed by this method. The experimental results that the pulse sequence is quite good.
1987, 36 (10): 1255-1263.
doi: 10.7498/aps.36.1255
Abstract +
The evolution of valence hand photoemission spectra in the formation of noble metal-GaAs (110) interfaces has been studied with 21.2 eV and 40.8 eV photons. For less than 0.5 mono-layer of deposited metals, the so-called atomic-like Ag 5s and Au 6s states have been observed. A maximum in the emission of the valence band of noble metals has been observed in the range from about 10 ? to a few tens ? of deposited metals. The experiment results are discussed with the point of view of metal clustering associated with interfacial reaction.
1987, 36 (10): 1264-1272.
doi: 10.7498/aps.36.1264
Abstract +
In this paper, based on the differential equations of Change rate of hole concentration for deep acceptor trap and excess hole located below quasi-Fermi level under equilibrium or non-equilibrium state (with light illumination), an exponential attenuation equation has been deduced. It is capable of explaining the effect of deep level trap on photo-pulse transient characteristics, satisfactorily. We indicate chat the deep trap is the primary cause of producing the long tail of attenuation curve. The photo-pulse transient characteristic curves of GaAs MESFET, GaAl-As TEGFET and Si JFET were measured. The experimental results could check the exactness of the theory. The effect of deep level depth ET, concentration NT and so on attenuation curves has also been discussed. The dependence of equivalent noise voltage Eeq on frequence for the above three devices were measured. The relations between equivalent noise current Ieq and f, and between Ieq and effect deep level concentration NT,eff were obtained using the equations in ref. (6). In this way, the effect of deep level trap on noise may be obtained. The relation between △NT,eff and drift of drain current △ID could be calculated. They were in well agreement with the experimental results. Hence, the increase of △ID also results from the deep level trap.
1987, 36 (10): 1273-1280.
doi: 10.7498/aps.36.1273
Abstract +
Based on a model a little bit complicated than that in ref. [2] , the mathematical method of ref. [1] was used to yield an universal condition of dispersion. By means of this condition, the surface plasmon spectra of the quasiperiodic semiconductor superlattice of type-I, type-II and II-VI compounds were discussed.The results show that bacause of the break of reflection symmetry in the plane perpendicular to the axis of the superlattice, when the surface is located at the Fm different interfaces of the primary cell, the spectrum of surface plasmon shows a great deal of patterns for each choice of sets of the parameters. (Fm is the Fibonacci number).
1987, 36 (10): 1281-1288.
doi: 10.7498/aps.36.1281
Abstract +
Transverse magnetoresistance in amorphous magnetic alloys (Fe1-xCox)82Cu0.4Si4.4B13.2 were measured at room temperature and in the magnetic field range 0-15 kOe. For large magnetic field, three various functional dependences of magnetoresistance on magnetic field strength have been found as follows: (1) △ρ/ρ approaches saturation. (2) △ρ/ρ increases proportionally to H2. (3) For x = 0.15, sharp △ρ/ρ peak appears at certain magnetic field strenght in spectial angular orientation of both magnetic and electric current. The case (3) is a magnetic breakdown phenomenon. Magnetic breakdown occurs at the gap between the spin-up and spin-down sheets of the Fermi surface. This gap is the spin-orbit gap and its magnitude is a sensitive function of magnetization. Hence the magnitude and wide of the magnetoresistance peak and the magnetic field strength at the peak point are functions of angular orientation of both magnetic field and electric current.
1987, 36 (10): 1289-1304.
doi: 10.7498/aps.36.1289
Abstract +
We have studied the aggregation of silver sol by mixing silver sol with several kinds of ions. We found that it is very difficult for the monovalent metal ions to make silver sol aggregate. The metal ions of the second main group can make silver sol aggregate and form fractal state. With the radii of metal ions increase, their ability of aggregation increases accordingly. The metal ion of the third main group A13+ can also make silver sol aggregate and form fractal state. As for acid radical ions, they can not make silver sol aggregate directly, but they can influence the speed of the aggregation and final state of silver sol. The simple explanations of these phenomena were given. We also found that the speed of aggregation and final state of silver sol were determinded by the state of silver sol and the proportion of metal ions in silver sol.
1987, 36 (10): 1305-1312.
doi: 10.7498/aps.36.1305
Abstract +
Combining the improved effective-mediume theory (EMT) with the feature of sensitive semiconductor ceramics, we proposed a simple and quantitatively physical model that can be used to describe the relation between micros tructure feature and proprety of sensitive semiconductor ceramics. We used this model to describe the electrical propreties of nonlinear ZnO ceramics by, and found that the results of the model are consistent with experimental results and the results obtained by the quentum theory of semiconductor conduction.
1987, 36 (10): 1313-1320.
doi: 10.7498/aps.36.1313
Abstract +
Following paper (I), we describe the electrical feature of thermal-sensitive, gas-sensitive and humiditysensitive ceramics by the microstructure-physical model of sensitive ceramics, and obtain some important results. These theoretical results are consistent with experiments, they provide a basis of the theory for materials design of sensitive ceramics. We expect that this model can be taken as the unified microstructure-physical model of this kinds of semiconductor ceramics.
