Vol. 40, No. 2 (1991)
1991, 40 (2): 169-174. doi: 10.7498/aps.40.169
In this paper, we use the renormalisation group approach and Monte-Carlo simulation to treat the problem of percolation on a two-dimensional square lattice with next-nearest-neighbour interactions. The critical probability pc and the critical exponents α,β,γ and so forth are obtained. It is shown that the two-dimensional percolation problem with next-nearest-neighbour interactions belongs to different universality class from that only with nearest-neighbour interactions.
1991, 40 (2): 175-181. doi: 10.7498/aps.40.175
The finite temperature self-consistent semiclassical equation is derived with the utilization of Skyrme force and semiclassical approximation. This equation is solved numerically by employing the imaginary time step method. The nucleon densities of some hot spherical nuclei are determined and the RMS radii are calculated.
In this paper, we discuss the physical mechanism of laser plasma wake wave and beat wave accelerators by means of theoretical analysis and particle simulation methods. The results show that: as long as laser plasma wave has Vph≈c and is strong enough, and with a proper transverse magnetic field applied, we may accelerate relativistic electrons to the order of magnitude of GeV within a distance of meters. We have also studied the problem of ES wave with low phase velocity generated by laser plasma Raman scattering to accelerate non-relativistic electrons by using particle simulation methods, and possibility of multistage, or multiwave, acceleration is explored as well. The results show that: taking the advantage of laser plasma wave accelerator, we will be able to get high energy electrons of the order of magnitude of Gev under ordinary laboratory conditions.
ATOMIC AND MOLECULAR PHYSICS
1991, 40 (2): 190-197. doi: 10.7498/aps.40.190
Here we present a unified theory of above threshold ionization (ATI) phenomena. Based on this theory, we can describe ATI processes in realistic atomic screen potentials and can also elucidate experimental observations of ATI phenomena. The ATI phenomena mainly involve two successive procosses: (1) Quantum transition processe from an initial field-free state to final strong laser field dressed states. (2) in order to descibe experimental observations, one must consider post-interactions between the escaping photoelectron and the strong laser fields, which are classic processes owing to ponderomotive forces generated by non-uniform laser fields.
1991, 40 (2): 198-204. doi: 10.7498/aps.40.198
The interaction between riboflavin and silver colloidal particles was studied with absorption and surface enhanced resonant Raman spectroscopy (SERRS). It was found that flourescence interference was completely quenched while Raman scattering was significantly enhanced upon addition of silver sol into ri boflavin aqueous solution. Tentative assignment of Raman modes was given. SERRS sp ectra suggest that Ag complexation of riboflavin in silver sol dose not resemble the aqueous solution complex of Ag. In addition, Raman bands below 1000 cm-1, which are mostly related to ring breathing and C-H torsion out of plane, were also obtained.
Positronium atoms are formed efficiently by slow positron beam hitting a solid target surface in vacuum. The fraction of positrons which formed positroniums is determined by applying the "peak method" to the energy spectra of the positron annihilation radiation measured at different target temperatures and incident positron energies. The fraction is dependent on the target material, temperature and incident positron energy. For germanium, the fraction is as high as 80%.
CLASSICAL AREA OF PHENOMENOLOGY
1991, 40 (2): 210-218. doi: 10.7498/aps.40.210
This paper studies the cavity field generated by injecting atoms, one at a time, initially in the excited state and operating at a one-step two-photon transition. The interesting features of photon statistical distribution in the cavity are found and discussed, the conditions of generating photon number state are shown.
1991, 40 (2): 219-225. doi: 10.7498/aps.40.219
By making use of the parametric-amplif ier model, we analyse the effect of space-charge wave in Raman free-electron lasers. R esults show that without taking the initial transverse velocity into account, kwv20>ωc is a necessary condition under which the scattered wave couples with the slow space-charge wave. The dispersion relation and gain of the scattered wave, as well as the matching condition between the scattered wave and the space-charge wave, are derived.
1991, 40 (2): 226-233. doi: 10.7498/aps.40.226
By means of the semiclassical method, we discuss the bistability in a two-photon laser with injected signal for the homogeneously broadened single mode ring cavity. It is demonstrated that in the resonant case one can find bistable states in a two-photon laser with injected signal. In the limit of "good cavity" and "bad cavity", we give a simple description of bistability leading to a predictions for the transient behavior of the output light and the hysteresis cycle by adiabatically eliminating the fast variables. It is found that the approach to the stationary state is monotonic in the low-branch and is oscillatory in the high-branch, and a critical slowing down occurs where the output field changes discontinuousiy.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1991, 40 (2): 234-242. doi: 10.7498/aps.40.234
We present in this paper the temporally and spatially resolved feature of the side scattered 3ω0/2 harmonic emission, induced by A single laser spot with ten-micron-radius-scale in a preformed laser plasma. The close relation of the harmonic emission with such a small scale laser self-focusing filamentation has been discussed in detail. It is suggested that the side scattered harmonic signal from a underdense region as low as 0.05nc may be caused by the Lang-muir wave and/or ion-acoustic wave scattering induced by laser dynamic filamentation.
THEORY OF DEGENERATE AND NEARLY DEGENERATE FOUR-WAVE MIXING IN PLASMAS——IN THE CASE OF TRANSMISSION GRATING CONFIGURATION
1991, 40 (2): 243-252. doi: 10.7498/aps.40.243
In this paper, the theory of degenerate and nearly degenerate four wave mixing in plasmas in transmission geometry is investigated. The universal set of four wave nonlinear coupled equations is obtained and its exact solution is found. The theoy can be helpful in developing various high speed nonlinear optical devices in the range of microwave frequencies.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
THE EFFECTS OF NITROGEN CONTENT OF a-SiNx:H ON THE INTERFACE PROPERTIES IN a-Si:H/a-SiNx:H SUPERLATTICES
1991, 40 (2): 253-261. doi: 10.7498/aps.40.253
The effects of nitrogen content on the interfacial properties in a-Si:H/a-SiNx:H superlat-tices have been studies by electroabsorption (EA) photothermal deflection spectroscopy (PDS), photoluminescence (PL) and infrared (IR). The density of interface charges Qs deduced from EA is approximately 1012cm-2. The density of interface states Ni estimated by PDS is ～1011cm-2 which is smaller by a factor of 5 than Qs. The nitrogen content x dependences of Qs, Ni and the relative peak intensity of luminescence Ipl exhibit similar behavior and show extreme values at x=xc which is defined as critical value of nitrigen content. The critical values of nitrogen content are in the x range of 0.85-0.95. The measurements of IR reveal that the absorption of N-H bonds increases rapidly with increasing x in the range of 0.6-1.0. The asymmetry of interfaces and a possible mechanism of presence of critical values are discussed-For interpretating the phenomena observed, a model of charged nitrogen dangling bond is suggested.
1991, 40 (2): 262-268. doi: 10.7498/aps.40.262
The dynamic viscosity and the steady-state viscosity are measured for the metallic glass Ni30Zr70. The dynamic viscosity increases linearly with the decrease of the heating rate as a result of the structural relaxation, and the temperature dependence of the dynamic viscosity can be described by the Arrhenius equation in the temperature range below Tg. The temperature dependence of the steady-state viscosity satisfies the Fulcher-Vogel equation at temperatures below Tg. From the high temperature at temperature of the onset of crystallization dynamic viscosity values with four heating rates, the equilibrium viscosity is determined. Over the temperature range of 63C to 670K, the temperature dependence of the equilibrium viscosity is well described by the Fulcher-Vogel equation.
1991, 40 (2): 269-274. doi: 10.7498/aps.40.269
One-dimensional tight-binding model and the one-electron chemisorption theory are used to calculate the chemisorption energy of CO or O on NixCu1-x surface under the average T-matrix approximation. It is found that the chemisorption of CO and O on NixCu1-x are strengthened with the increase of bulk Ni concentration. The Cu segragation to the NiCu alloy surface may weaken the chemisorption.
The Au/a-Si:H contact has been investigated by XPS and AES. It is found that the metal cluster occurs, at initial formation process of Au/a-Si:H interface, and after exceeding the critical Au deposition value, the Vinterdiffusion and chemical reaction of Au and Si begin and Au-Si intermixing region is formed. Furthermore, the experimental results of photoemission study confirm that Si islands are formed after annealing the interface of Au/a-Si:H.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1991, 40 (2): 281-288. doi: 10.7498/aps.40.281
The electrical resistivity of the heavy-fer mion alloy system is calculated through the Yoshimori-Kasai model with the application of the slave-boson technique. The residual resistivity of the system is found in the mean-field approximation by using the CPA method-The low-temperature resistivity maximum in the concentrated alloy is aslo obtained as the Gaussian fluctuation of the slave-boson field is included.
1991, 40 (2): 289-296. doi: 10.7498/aps.40.289
The microstructure and current transport behavior in the thermally nitrided silicon oxide (SiOxNy) thin films have been studied and a new model is proposed to explain the current transport behavior of the films. In particular, the model includes the case in which the external applied high field rises up to the value just before the occurance of intrinsic breakdown. The theoretical result of the new model agrees well with the experiment. Finally, the significant current enhancement and trapping ledge phenomenon in the I-V characteristics of the films have been explained satisfactorily using this new model, and the influences of the external applied field and the electron trap on the current transport behavior in the films are also discussed.
1991, 40 (2): 297-302. doi: 10.7498/aps.40.297
High-quality single phase polycrystalline sample of 110K superconductor (Bi,Pb)2Sr2Ca2Cu3Oy was prepared, the temperature of zero resistance of which is 107K. In this paper, the formation and transformation of the 2201, 2212 and 2223 phase, and the influence of quenching temperature are discussed. The measurement of complex susceptibility shows the strength of Josephson coupling among the superconducting grains depends on the process of sample preparation. The specific heat jump is △c(107K) =5.3J/molK, and the Sommerfeld cntant is γ = 34.6mJ/molK. The specific heat jump is related to the heat treatment of samples strongly. The eletron diffraction analysis and measurement of the oxygen content of these samples are made. The relationship between the oxygen content and the superconducting volume fraction is also discussed.
MAGNETIC PROPERTIES AND CONVERSION ELECTRON M?SSBAUER SPECTROSCOPY OF COMPOSITIONALLY MODULATED FeBSi/Si AMORPHOUS FILMS
1991, 40 (2): 303-309. doi: 10.7498/aps.40.303
The compositionally modulated FeBSi/Si amorphous films were prepared by rf sputtering. The saturation magnetization of modulated films decreases exponentially with increase of the thickness of Si layers. This is caused by the dead layers. The M?ssbauer spectra measurements showed that the dead layers are the paramagnetic phase formed by the interdiffusion of Fe and Si atoms at the interfaces. The size effect was observed in the FeBSi/Si films. The size effect depends only on the thickness of FeBSi layers, and the dead layer effect depends on both the FeBSi layer thickness and Si layer thickness.
M?ssbauer spectra were taken at 4.2 K and 290 K for the bcc and fee Fe1-xPdx alloys produced by vapor quenching. The hyperfine interaction parameters and hyperfine field distribution curves were obtained with spectrum fitting method. With increasing x, the average hyperfine field, Hhf increases in bcc Fe1-xPdx alloys, while Hhf decreases in fee alloys. The concentration dependence of Hhf can be explained by using a semi-empirical formula.
A RESEARCH OF THE CORRELATION BETWEEN SURFACE TOPOGRAPHY AND ANGULAR DISTRIBUTION OF SPUTTERED ATOMS
1991, 40 (2): 316-322. doi: 10.7498/aps.40.316
The angular distributions of sputtered atoms of cadmium have been measured with 27 keV Ar+ ion bombardment at normal incidence with different target temperature by using collector technique and RBS analysis. After the sputtering experiment the surface structures have been observed using scanning electron microscope. For all samples the angular distributions are over-cosine. However, the values of the deviation △ from the cosine distribution at the axis of polar angle of 0°is not all the same. The deviation △T at the target temperature of 150℃ △R is smaller than that at room teperature. ie. △TR. A simple model is proposed to explain the formation of pattern of angular distribution.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1991, 40 (2): 323-328. doi: 10.7498/aps.40.323
Time-dependent development of interface morphology from initial perturbation of a planar interface to a steady periodic array of cells or dendrites was directly observed during directional solidification brocess of a transparent model alloy, succinonitrile -1.1 wt% ethanol. The following results are obtained: 1) The measured wavelength of initial perturbation of planar interface instability is within the expected wavelength range by the MS theory, but not the same as the expected wavelength with the fastest amplitude developing speed. 2) During the initial stage of a planar interface instability, the developing speed of perturbation amplitude is indeed a linear function of the amplitude, but the measured value of the amplitude developing rate is much smaller than the theoretical value. 3) The features of morphology development of cells and dendrites are different from each other, and the main cause leading to the different developing behaviour is that the relative scale of the steady primary spacing and the initial perturbation wavelength is different in the two cases.