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Vol. 28, No. 6 (1979)

1979-03-20
CONTENT
THE EFFECT OF THE LATTICE VIBRATION ON THE EXCITON MOTION
GU SHI-WEI
1979, 168 (6): 751-758. doi: 10.7498/aps.28.751
Abstract +
In this paper, the effect of the lattice vibration on the exeiton motion is discussed by a perturbation method that was developed to investigate the problem of plarons by Haga. Our previous work is generalized to the case that the electron mass and the hole mass are not equal. When we neglect the interaction between phonons of different wave vector in the recoil process, the ground state energy, effeetive mass, reduced mass and inner potential energy are derived. It is shown that the effective mass of the exeiton depends on the interaction between the electron, hole and the phonons reduced mass of the exciton not only depends on the interaction between the electron. Hole and the phonons, but also on the electron and hole mass ratio; the formation of a self trapping exciton is not determined by the magnitude of the interaction between the electron, hole and the phnon, but by the electron and hole mass ratio. A exciton is self trapping when the electron and hole mass ratio is in the range 0.261 e/μh<3.83.
A NEW MODE OF FOUR-POINT PROBE TECHNIQUE FOR THE MEASUREMENT OF SEMICONDUCTOR SHEET RESISTANCE
SU CHANG-HOU
1979, 168 (6): 759-772. doi: 10.7498/aps.28.759
Abstract +
A new method for measuring sheet resistance of semiconductor using four-point probe has been developed. Its characteristies are as follows, (a) the distances between probes can be unequal for the large thin slices as well as for the samples with finite extent. The result obtained does not depend on the probe spacings. Errors due to unequal probe spacings are eliminated; (b) it is not neccesaxy to take into account the geometry corrections for the rectangular and circular small specimens. The knowledge of its dimensions, so that, is needless. The value of the resistance can be determined from electrical measurement only.
INVESTIGATION OF THE STRUCTURE AND THE PROCESS OF PHASE TRANSFORMATION ABOUT δ-FeOOH
DU YOU-WEI, ZHANG YU-CHANG, JIAO HONG-ZHEN, LU HUAI-XIAN, LI ZHENG-YU, GU BEN-XI
1979, 168 (6): 773-782. doi: 10.7498/aps.28.773
Abstract +
The structure of δ-FeOOH and the process of the phase transformation were studied by means, of thermogravimetric plots, differential thermal analysis, magnetic analysis, X-ray Diffraction and Mossbauer effect measurement.
GROWTH AND CHARACTERISTICS OF LITHIUM NIOBATE PLATE CRYSTALS
ULTRASONIC PIEZOELECTRIC MATERIALS GROUP
1979, 168 (6): 783-790. doi: 10.7498/aps.28.783
Abstract +
Growth of lithium niobate large plate crystals was achieved by using the Wet-ted-Die Technique. Their dimensions were about 200 mm long, 20 mm in width and 3 mm thick. Their properties was found to be the same as those of cylindrical crystals. We measured the density ρm of the melt of lithium niobate and its surface tension a. The results are: ρm= 3.57×103kg/m3, α = 204 dyne/cm at 1270℃, and ρm= 3.42×103kg/m3, α = 192 dyne/cm at 1300℃.
THE PRESENCE OF Si-H BONDS IN Si SINGLE CRYSTALS AND ITS INFLUENCES
CUI SHU-FAN, GE PEI-WEN, ZHAO YA-QIN, WU LAN-SHENG
1979, 168 (6): 791-795. doi: 10.7498/aps.28.791
Abstract +
The presence of Si-H bonds in hydrogen FZ silicon single crystals was confirmed by measurements of infrared absorption spectrum. Three characteristic absorption peaks were found at 4.51, 4.68 and 5.13 μm. By analysing theoretical calculations, it is believed that hydrogen atoms in silicon lattice are situated on several interstitial sites. Investigation showed that the Si-H bonds formed in crystal growth influences implicitly on the crystal perfection, and it was discovered that there exists a close relationship between the production, of defects by hydrogen and the breakdown of hydrogen-associated bonds at high temperature.
THE TRANSDUCER BANDWIDTH OF ACOUSTO-OPTIC DEVICES AND THE DETERMINATION OF THE LAYERS' THICKNESS
XU JIE-PING
1979, 168 (6): 796-806. doi: 10.7498/aps.28.796
Abstract +
According to the Mason's equivalent circuit of piezoelectric transducer, we have calculated the functional relationship between transducer loss TL and normalized frequency f/f0 for the 36°y-cut LN/PM and the x-cut LN/TeO2 acousto-optic devices, with different layer materials and thickness. From these calculations, we can determine the thickness of the various layers rationally and the transducer bandwidth of the devices accurately. We give also the loci of the electric input- impedence Zi with f/f0 on the Smith chart, which can be used as theoretical foundation of quality tests for the devices.
A THEORETICAL MODEL FOR TRANSVERSE-DISCHARGE FLOW TYPE CO2 LASERS
GAO ZHI, LIN LIE, SUN WEN-CHAO
1979, 168 (6): 807-823. doi: 10.7498/aps.28.807
Abstract +
A theoretical model is proposed to analyse the transverse-discharge flow type CO2 lasers. Theoretical expressions are obtained for predicting gain-saturation and output power of flow type gas lasers, these expressions are in agreement with the well-known formulae of non-flowing gas lasers, but the former contains correction terms related to pumping action in the upstream direction of the cavity and the gas flowing effect. Based on the analysis of the variation of intensity in the direction of flow, we derive the limiting values of stauration intensity and other parameters which were attained as the flow speed was being increased. Reliability of the semi-empirical analysis suggested, in literature [1-3] for the flow type laser performance predicted by choosing an average gain-coefficient anl adopting the formulae of non-flowing gas lasers has been proved. The qualitative analysis presented in article [4] is developed into a quantitative calculation. The present model should be used in place of the semi-empirical one, since the formulae deduced are as simple as those for the non-flowing gas lasers. The results computed for both amplifier and oscillator cavities using the present model are in agreement with experimental data [1, 18-21].
THE MEASUREMENT OF ELECTRON TEMPERATURE OF PLASMA BY LASER SCATTERING AND THE ENERGY LOSS OF θ-PINCH PLASMA
YAO XIN-ZI, ZU QIN-XIN, XU YAO, GAO PENG, HU FENG-JIE, LI BAO-HUAN
1979, 168 (6): 824-832. doi: 10.7498/aps.28.824
Abstract +
In this paper, the measurement of electron temperature of the θ-pinch plasma by means of Thomson scattering of ruby laser is described. The experimental data of clectron temperature in θ-coil midplane are analysed using the one-fluid model. The experimental results show that the electron temperature is much less than the theoretical value in the ease of adiabatic compression, and the experimental data are in good agreement with the theory when the loss of the electron thermal conduction is considered. The conduction coefficient calculated according to the one-fluid model is larger than the Spitzer's classical value by a factor of 2-3. After about 3 μs, the electron temperature dropped sharply, the thermal conduction theory holds no longer. A possible explaination is that the end loss becomes dominant, and thus the plasma collapses rapidly.
MHD EQUILIBRIUM AND STABILITY OF AXIAL SYMMETRIC TOROIDAL PLASMA WITH AN ELLIPTIC CROSS SECTION OF TRIANGULAR DEFORMATION
MA TENG-CAI
1979, 168 (6): 833-840. doi: 10.7498/aps.28.833
Abstract +
Expanding the magnetic flux in terms of the deviation from the magnetic axis, we have studied the MHD equilibrium and localized mode instability of an axial symmetric plasma torus with a small triangular and elliptical deformation on its cross-section. The optimization of the configuration has been analyzed and an optimal factor of the triangular deformation has been given. Our analysis shows that it is possible to strengthen ohmic heating substantially by selecting suitable factors of the triangular deformation.
ON HYBRIDIZED BAND AND THE INTRINSIC UPPER LIMIT OF ELECTRON-PHONON COUPLING
YIN DAO-LE, ZHANG LI-YUAN, DAI YUAN-DONG
1979, 168 (6): 841-852. doi: 10.7498/aps.28.841
Abstract +
The general properties of hybridized conduction bands were studied in the LMTO representation. General expressions of the density of states N(E) and partial wei-ghts |Blik|2 were derived. Introducing a "phase function" yl which corresponds to a certain radial wave function φl, it permits one to derive an analytical approximation for the logarithmic derivative of φl and the phase shift due to a spherically symmetrical potential. Then the analytical behaviour of electronic factor η in electron-phonon coupling was studied. We verified the presence of an "intrinsic upper limit" for η and evaluated its order of magnitude. Discussions were given for the general rules affecting η and the comparison with experiment. As for the relation to searching for strong coupling and high Tc, we emphasized the role of magnitude of hybridization, especilly enhancing the f-component in a d-like conduction band.
APPLICATIONS OF THE SERIES FORMULA OF SUPERCON-DUCTING CRITICAL TEMPERATURE
JI GUANG-DA, CAI JUN-DAO
1979, 168 (6): 853-864. doi: 10.7498/aps.28.853
Abstract +
Using the series formula of superconducting critical temperature (1), we have obtained an expression of isotope effect for B-type superconductors. In both cases of μ*= 0 and μ*≠0, we have obtained a series expression for the upper limit of Tc. The agreement between the results of series formula and numerical solution is quite good. Finally, with μ*= 0, we have discussed the relation between Tc and various spectrum parameters. It is apparent from the series expression that when fixing different parameters the behaviour of Tc is completely different, hence we have made a general interpretation for the different conclusions of other authors about the effect of phonon spectrum on Tc. We emphasize that, in most cases, the series formula (1), which we took up to first two terms only, can be used as a good approximation for numerical solution,so that the series formula is simplified greatly. It may be predicted that by using this simplified formula we can investigate many other problems.
BRIEF REPORT