Vol. 45, No. 2 (1996)
1996, 45 (2): 177-184. doi: 10.7498/aps.45.177
The Hawking radiation and the Starobinsky - Unruh process of Dirac particles in space-time determined by the generalized spherical symmetric evaporating charged (GSSEC) black hole are studied.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
1996, 45 (2): 185-191. doi: 10.7498/aps.45.185
The energy spectral problem of the ultrarelativistic quantum systems is investigated. A typical ultrarelativistic system (the Lund model) is solved exactly and a new virial theorem is proved, these are to show the influence of the form of kinetic energy to the energy spectra.
CLASSICAL AREA OF PHENOMENOLOGY
1996, 45 (2): 192-200. doi: 10.7498/aps.45.192
The radiations fields of FELs are analysed by using the classical electrodynamics. The general characteristics of radiation fields are discussed, and the mathods of self-consistent solutions for the radiation fields of FELs are establised systematically by using the Maxwell equations, wave equation, continuity equation of electron, Lorentz force equation and energy equation of relativistic electrons.
DEGRADATION OF THE POWER OF COHERENT HARMONICS GENERATED BY THE FUNDAMENTAL MODE BUNCHING AND ELECTRON BEAM QUALITY
1996, 45 (2): 201-204. doi: 10.7498/aps.45.201
The thermal effect of the electron beam on the power of coherent harmonics generated by the fundamental mode bunching has been researched analytically, and compared with the mechanism generating coherent harmonics by the external source prebunching.
1996, 45 (2): 205-209. doi: 10.7498/aps.45.205
Wavelength match experiment was carried out with a soft X-ray crystal spectrograph for three pumping and absorbing line pairs at wavelengths around 4.5 nm:SiXII3d-2p,4.4021 nm, MgX2s-4p, 4.4050 nm; CuXIX4f-3d, 4.7329 nm, MgX2p-4d, 4.7310 nm and AlXI3p-2s,4.8338 nm and MgIX2s2-2s4p,4.8340 nm.The second line pair was found in this experiment and never appeared in published work. The pros and cons these line pairs for photo-resonant X-ray lasers were compared and discussed.
Excited state degenerate four-wave mixing in a four-level saturable system is treated theoretically and experimentally. The results show that the external pump feild influences intensely the intensities of the PC signals.
1996, 45 (2): 214-221. doi: 10.7498/aps.45.214
Based on semiclassical approach, the transport equations of chirped-pulse amplification are presented. Time-and spectral-domain evolution of chirped pulse and effects of self-phase modulation in multipass amplification are numerically analyzed. Theoretical results show that the new frequency chirp induced by self-phase modulation changes the instantaneous frequency of chirped pulse and affects the quality of amplified pulse. The study of chirped-pulse amplification in the gain saturation regime shows that the linear frequency chirp of input pulse tends to suppress the effects of self-phase modulation.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
NUMERICAL SIMULATION AND SCALING LAW OF ABSORPTION OF GOLD DISK TARGETS IRRADIATED BY 1.05 AND 0.53μm LASER
1996, 45 (2): 222-231. doi: 10.7498/aps.45.222
Au disk targets were irradiated with -0.8 ns, 1.05 and 0.53 μm laser. The intensity and angular dependence of absorption were studied experimentally. The experimental results of absorption by laser-produced plasma are introduced in this paper. The measured absorption with plasma calorimeters accord with one-dimension planar simulation. The experiment and theory show that collision absorption is the main absorption mechanism. A scaling law of absorption has been suggested based on the careful analysis of the experimental results.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1996, 45 (2): 232-238. doi: 10.7498/aps.45.232
The Raman spectra of Sr1-xBaxNb2O6(SBN) and (K1-yNay)z(Sr1-xBax)l-zNb2O6(KNSBN) crystals have been obtained and discussed based on the space group theory and lattice dynamics. It provides scientific basic for an improvement on SBN and KNSBN by ion doping.
1996, 45 (2): 239-243. doi: 10.7498/aps.45.239
The behaviors in annealed Ge/Fe multi-layer have been investigated. It is found that the temperature of crystallization and compound-production at the surface is higher than that in the bulk. The abnormal Raman spectra are analyzed and the relationship between the phases and the magnetism during annealing is also discussed.
1996, 45 (2): 244-248. doi: 10.7498/aps.45.244
The I-V curves of the initial stage of porous silicon formation have been measured, and the amount of charge transfer for silicon atoms adsorbed different elements has been calculated. It was pointed out that there would exist a dipole layer at c-Si/electrolyte interface, which affected the formation and properties of porous silicon. The effects of HF concentration, current density and light illumination on material formation were also discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1996, 45 (2): 249-257. doi: 10.7498/aps.45.249
An analytical Green's function approach to the study of the electrical transport in bimetallic films is presented. Taking into account the quantum size effects and considering three types of scattering from bulk impurities, rough surfaces and a rough interface, we calculate the one-partical Green's functions and the in-plane conductivity, yielding a new formula for conductivity in bimetallic films. It is found that in the thin-film limit and to the lowest order in the surface and interface scattering, the total conductivity is given by a sum of conductivities of all the subbands and for each subband the scattering rates due to the impurities, surfaces and interface are additive.
1996, 45 (2): 258-264. doi: 10.7498/aps.45.258
The photovoltage spectra of GaAs/AlGaAs multiple quantum wells (QMWs) in which the substrates are semiinsultion GaAs have been studied at temperatures ranging from 18 to 300 K. A series of distinct excition absorption peaks were observed. At low temperature, the photovoltage spectra reflect the steplike distribution of state density of QMWs. It is believed that the photovoltage spectroscopy is an effective technique for inspecting the growing quanli-ty of QMWs and superlattice. The changes of photovoltage with temperature and the mechanism of photovoltaic effect are also discussed.
ELECTRICAL CHARACTERIZATION OF SOLID C60/Si HETEROJUNCTIONS——RECTIFYING PROPERTIES, ENERGY-BAND MODELS, AND BIAS-TEMPERATURE EFFECT
1996, 45 (2): 265-273. doi: 10.7498/aps.45.265
This work investigates electrical properties of contacts between undoped solid C60 and n-or p-type Si. Current-voltage measurements show that the two contacts result in strong rectification with opposite conduction directions, indicating two different kinds of barriers for carrier transportation at the interface of the two contacts. Current-temperature measurements show that the current is an exponential function of reciprocal temperature, from which we estimate the effective barrier height to be 0.30 and 0.48 eV for C60/n-Si and C60/p-Si, respectively. Within energy-band models we interpret successfully the above experimental results. Based on the energy-band model and experimental data we derived the electron affinity of solid C60 film to be 3.92 eV and its energy gap to be below 1.72 eV. Highfrequency capacitance-voltage measurements show that biastemperature treatments have considerable effect on the C-V characteristics of the heterojunction. Assuming the existence of mobile negative charges in the solid C60 film we explain the effect successfully and estimate the density of the negative charges to be 3.1×1012cm-2. By use of the C-V results we determine the dielectric constant of the solid C60 film to be 3.7±0.1 in the temperature range of 300-370 K.
1996, 45 (2): 274-282. doi: 10.7498/aps.45.274
The quantum confined stark effect of InGaAs/InAlAs MQW heterostructures lattice-matched to InP substrate, grown by Chinese-built molecular beam epitaxy (MBE) system, is observed by absorption photocurrent spectra measurements, as well as the anisotropic elec-troabsorption of MQWs. The structure parameters of the epitaxied materials, which can be used to fabricate waveguide MQW electroabsorption modulators, were determined from double crystal X-ray diffraction measurements and computer simulations. The theoretical calculations of absorption-edge red shift compared with experimental results shows that the built-in-potential of the p-i-n junction can not be neglected.
1996, 45 (2): 283-290. doi: 10.7498/aps.45.283
The resistive transition broadening of high Jc Ag-sheathed Bi(2223) tape has been systematically investigated in the field range of 0 to 1T. The experimental result shows that the resistive transition is of the thermally activated behavior. The relation between the flux pinning and the temperature has been studied. The temperature dependence of resistance is R(T) = R0exp [-μ0(1-T/Tc)n/kT] ,where n=4.5 for H//ab plane and n=3 for H⊥ab plane. When the magnetic field is parallel to ab plane, the dissipation is independent of the Lorentz force and only depends on the magnitude of the magnetic field parallel to ab plane. This behavior can be explained in terms of thermally activated pancakelike vortex-an-tivortex pair model. The mechanism of the flux pinning of the Bi-system material is discussed .
1996, 45 (2): 291-296. doi: 10.7498/aps.45.291
The magnetic properties of lithium ferrite nanocrystallites ranging from 9.1 to 860 nm have been studied. The specific saturation magnetization σs of these nanocrystallites decrease lineally with the nanocrystallite size.The specific magnetization versus temperature curves (T) and M?ssbauer spectra of sample A (diameter D = 860 nm), sample B (D = 11.8 nm) and sample C (D = 9.1 nm) have been measured. It is found that the Curie temperatures of samples B and C are 50℃ lower than that of sample A. From the σ(T) curve of sample C, it seems that sample C consists of two magnetic phases. These phenomena have been discussed with the superparamagnetism and the surface magnetism of sample C.
1996, 45 (2): 297-303. doi: 10.7498/aps.45.297
The bright and stable porous silicon have been obtained by using damp oxidation at moderate temperature. EPR measurements showed that the density of Si dangling bonds in the sample is lower than that by dry oxidation. We also took FTIR measurements and concluded that the stabilization of the photoluminescence from porous silicon is due to the formation of SiH(O3), SiH(SiO2) and SiH(O2) structure.
1996, 45 (2): 307-313. doi: 10.7498/aps.45.307
The room-temperature photoluminescence (PL) spectrum of the modulation-doped strained In0.60Ga0.40As/In0.52Al0.48As multiple quantum wells (MQW) is reported. In addition to two strong PL peaks related to the recombination between electrons in the first (n = 1), second ( n = 2) subbands and heavy holes in the first ( n = 1) subband, a weak PL shoulder related to the recombination between n = 1 electrons and n = 1 light holes is obsevered at low temperatures. We demonstrate that the main mechanism of the decrease in radiative QW recombination efficiency is due to the carrier trapping on the misfit dislocations, based on the temperature and excitation power dependence of the PL peak intensity and energy and the steady-state PL model.
The nuclear magnetic resonance spectrum of 57Fe nuclei in γ - Fe4N alloy has been observed by the coherent spin-echo method. The peculiar line shape of nuclear magnetic resonance of Fe Ⅱ arises from the anisotropic hyperfine interactions and the domain wall excitation.
1996, 45 (2): 318-323. doi: 10.7498/aps.45.318
It is experimentally investigated by glancing angle X-ray diffraction (GAXRD) that the phase transition temperature and structure parameters of surface layer and differing from those of bulk layer in polycrystalline PbTiO3 ferroelectric thin film. The polycrystalline ferro-electric thin film is phenomenologically treated as a double layers structure: the surface layer is characterized as fine crystalline and low stressed, the bulk layer is characterized as large crystalline and high stressed. According to the influences of size and stress effects, the feature of phase transition of PbTiO3 polycrystalline ferroelectric thin film is described.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
A vertical gradient freeze apparatus was set up to investigate the crystal growth in high magnetic field. In the presence and absence of a magnetic field, temperature profiles were measured from solid-liquid interface to over Te-doped InSb melt, and InGaSb with low GaSb mole fraction and Te-doped InSb crystals were grown. The results of investigation show the high magnetic field of 8.00T can improve the quality of InGaSb crystal and the homogeneity of axial profile of Te impurity. These results are considered to be the consequence of the improvement of stability and the reduction of convective velocities of the melts in the high magnetic field.
MODELLING OF MULTI-ION-BEAM REACTIVE COSPUTTERING OF METAL OXIDE THIN FILMS (I)——ESTABLISHMENT OF THE MODEL
1996, 45 (2): 330-338. doi: 10.7498/aps.45.330
Reactive sputtering is a very useful technique for fabricating oxides and other compound thin films. Very recently, we developed a technique named multi-ion-beam reactive conputtering (MI-BRECS) for preparing multi-component metal oxide thin films. In order to promote the development of this technique, it is necessary to investigate the mechanisms of thin film growth of reactive cosputtering. Based on the well-known gas kinetics, we established a fundamental model of multi-ion beam, multi-target reactive cosputtering under stable sputtering circumstances, and obtained the relationships between both the deposition rate and composition of thin films and the controllable reactive cosputtering parameters. This model reveals the essential parameters that affect the composition of thin films and the methods for controlling the deposition rate and the composition of thin films can be obtained from the model.
1996, 45 (2): 339-344. doi: 10.7498/aps.45.339
The total-energy change is systematically evaluated in this paper when the thin ZrO2(T) ellipsoidal plate at different orientation transforms into ZrO2(M) under extension, compression and shear stresses. The optimal orientation of Martensitic uncleation is determined by using the oriterion of minimum energy. The numerical results show that the shear strains resulting from the transformation affect obviously the orientation of Martensitic nucleation and the critical stresses inducing transformation are very different.
MODELLING OF MULTI-ION-BEAM REACTIVE COSPUTTERING OF METAL OXIDE THIN FILMS (Ⅱ)——NUMERICAL CALCULATION AND RESULTS DISCUSSION
1996, 45 (2): 345-352. doi: 10.7498/aps.45.345
The numerical calculation for the model of a multi-ion-beam reactive cosputtering (MI-BRECS) system which we presented very recently in a related paper has been carried out with the parameters adopted in our experiments to prepare PbTiO3 thin films by using Pb and Ti metal targets and MIBRECS technique. The relationships among the sputtered ratio Ri of each target, the partial pressure p of reactive gas in the deposition chamber, and the coverage ratioes Zsmi, Zsli, and Zshi of the simple substances and oxide compounds of Pb and Ti on the substrate surface, with the total reactive gas flux Q and the densities Ji of the sputtering ion beam (both of which can be adjusted independently) are obtained respectively. The calculated results reveal the hysteresis effect which is an essential characteristics in a reactive sputtering, and show that there is a coupling and interaction among the processing parameters in ion beam reactive cosputtering. The relations among the atom ratio and the chemical valences of the elements in prepared thin films with the controllable processing parameters in ion beam reactive cosputtering are obtained, and the method to control and adjust a MIBRECS system for stable reactive cosputtering process is pointed out. The obtained results a-gree with our experiments.