Vol. 36, No. 11 (1987)
An experiment has been conducted on CT-6B tokamak in order to study the effect of discharge conditions, such as filling gas pressure, toroidal field, stray magnetic fields and loop vvoltage, on the breakdown. It is found that the dependence of breakdown voltage on the vertical stray field is obviously different from that on the horizontal stray field. The main experimental results are discrepant from the Townsend discharge model. The distribution function of electrons during the breakdown phase has been solved by using a Monte-Carlo code and the breakdown condition deduced from the Townsend model has been revised.
EXPERIMENTS ON THE WAVELENGTH AND INTENSITY DEPENDENCE OF LASER -PLASMA INTERACTION USING HIGH-SPEED SHADOWGRAPHY
1987, 36 (11): 1395-1400. doi: 10.7498/aps.36.1395
We have carried cut experiments on laser-driven shock wave propagation in a transparent target using high-speed shadowgraphy. The results of the following studies are obtained: 1) A comparision of shock wave pressures at the two wavelengths (λ =1.3μm and λ = 0.44 μm). 2) Scaling of shock wave pressures in dependence on the absorbed laser intensities of the targets.
STRUCTURE ANALYSIS OF Si(111)2×1 SURFACE AND THE EFFECT OF 1×1 DOMAIN WITH LOW-ENERGY ELECTRON DIFFRACTION
1987, 36 (11): 1401-1407. doi: 10.7498/aps.36.1401
One of the problems in surface physics which has not been solved for a long time is the atomic structure of reconstructed Si(lll)2×l surface. Basing upon the calculations on dynamics of low energy electron diffraction (LEED), we analysed the intensity-voltage curve in detail to test a lot of proposed models. The buckling π-chain model has been confirmed by our results. The atomic coordinates down to the sixth layer have been further modified, so that the agreement between theoritical calculation and experiment has been improved. The most salient feature of our optimum structure is a buckling of 0.44 ?. Finally, it has been shown that the existence of relaxed 1×1 domain in Si(lll)2×l surface caused a significant effect on the results. The R-factor of integral beam will be reduced considerably by taking into account the existence of relaxed 1×1 domain.
1987, 36 (11): 1408-1415. doi: 10.7498/aps.36.1408
Systematic studies on the structure of defects in InP caused by electron irradiation are conducted basing on the experimental measurements and theoratical calculations. The introducing rates and annealing out temperatures of In and P vacancies are estimated using proper theoratical models. These calculations reveal that after room temperature irradiation only complexes may exist. It is also supported by our experimental data that the sum of introducing rates of three detected levels are less than the theoratical value calculated for single vacancies.According to our equation on the relation between interface states and DLTS signal and result of computer calculation we believe that the broad peak appeared in DLTS diagram before irradiation is related to interface states. Its disappearance after electron irradiation suggests the reduction of interface state, this is further comfirmed by the reduction of surface recombination rate derived from the result of surface photo voltage measurement.
1987, 36 (11): 1416-1426. doi: 10.7498/aps.36.1416
Optical third harmonic radiation has been measured in reflection from Surfaces of Single crystal and ion implanted silicon samples. As was proved in our theoretical Calculation, the linearly polarized third harmonic intensity exhibits the rotational symmetry of the crystal as the crystal rotates about its surface normal. There is a critical implant etose in lightly implanted samples. The rotational dependence of the thirel Larmonic radiation is found to vanish when the ion dose exceeds the critical value. As a function of the implant dose, the third harmonic intensity is very sensitive to lattice damage. It is possihle to use the third harmonic technique for monitor of ion implant uniformity in semiconductor device technology.
INFRARED ABSORPTION OF DOPED SILICON PASSIVATED BY ATOMIC HYDROGEN, DEUTERIUM AND IMPLANTED BY PROTON
1987, 36 (11): 1427-1432. doi: 10.7498/aps.36.1427
FTIR was employed to study doped silicon passivated by atomic hydrogen, deuterium and implanted by proton. The localized vibrational modes of [BD] pairs, 1.560 cm-1 and 1263 cm-1, were excited with different passivation conditions of atomic deuterium. This shows that there are at least two possible positions for deuterium atoms around acceptor B. IR absorption spectra of doped silicon implanted by proton are different from that of undoped silicon, the hydrogen atoms prefer bonding around B acceptors. Only 1% implanted hydrogen atoms were turned into photoactive centers, most of implanted hydrogen atoms formed non-photoactive cen-ters, they might be hydrogen molecules, Hz.
1987, 36 (11): 1433-1440. doi: 10.7498/aps.36.1433
Using the Green function technique, the H-F ground state energy of the symmetric Anderson lattice is caolulated. Then the correlation energy, ground state energy, local moments, charge-and Spin-fluctuations of the correlation ground State are caclulated with the local approximation. Corresponding analytical formulas are obtained for a rectangular density of state. The result indicates that local moments decrease with decreasing value of the one-site f-f coulomb interaction U and or increasing value of the d-f hybridization strength V.
1987, 36 (11): 1441-1450. doi: 10.7498/aps.36.1441
The nonlinear behavior of ultrasonic absorption in glasses below 2 K is analysed by combining the two-level systems model and the infrared divergence theory. A modification of the existing tunneling two-level model of Jackie et al. is given. The Bloch equations are used as the macroscopic equations of the "magnetization" and all quantities in the equations as en-sebmble averages rather than a state expectation value. With this modification, and the defect state as a pseudo-spin in the local fluctuation field, the relation between the angle diffusion of the spin and the temperature at low temperatures is deduced. The theoretical absorption curve obtained is consistent with the experimental data. The observed T-0.7 rule of the resonance absorption under weak excitation and the proportional relation of the saturated absorption to ω2 are also explained.
1987, 36 (11): 1451-1458. doi: 10.7498/aps.36.1451
With the analysis of eigenvalues, it is found that a Hopf bifurcation would occur from the steady state of a dissipative three-wave interaction, so long as the contraction rate of its volume in phase space is low enough. The critical value of the contraction rate and the frequencies of the oscillation obtained from the eigenvalues are in good agreement with the results of solving the dynamk equations in the linear stage. It is also shown that no pitchfork bifuraction would occur.
1987, 36 (11): 1459-1471. doi: 10.7498/aps.36.1459
From the basic principles of statistical physics, we have obtained the more general conditions that the convolution law of the density of states of the system and its subsystems or that of the high-dimensional system and low-dimensional system is satisfiled. We also analysed the transition of densities of states from the l-dimension to the 3-dimension in the free electron and tigkt-binding periodic systems.
1987, 36 (11): 1472-1475. doi: 10.7498/aps.36.1472
XPS was used to study the electronic structure of the amorphous rare earth alloy TbxCo1-x. We found that there is no significant difference in the band structure of the alloy and the core level spectra of Co and Tb between the amorphous and crystalline states. This implies that the charge transfer between Tb and Co is the same in the two states. The difference in magnetic properties for these states thus can not be explained by the different amount of charge transfer in them.
The structure of lithium borovanadate (Li2O-B2O3-V2O5) glasses was studied by 11B CW-NMR technique. The fractions of BO4 and BO3 units were measured and analyzed. Basing on a FDB model, the structural model of lithium borovanadate glasses was proposed.We showed that V2O5 shared Li2O with B2O3, and combined with B2O3 in the form BVO4.5. The (N4)max are approximately constant with different K. According to this experimental result, it was deduced that there is no Reedmergnerite unit in lithium borovanadate glasses. We also learnt that without Li2O, V2O5 and B2O3 could not combine directly.
1987, 36 (11): 1481-1484. doi: 10.7498/aps.36.1481
By calculating the vibrational entropy change during hole transition for Fe-center, it is shown that the acceptor state of Fe-center is antibonding; The enthalpy and Gibbs free energy change and their temperature dependence caused by hole transition are calculated and compared with experimental data. From the results, it is reasonably well understood that activation energy obtained by thermal emission rate for Fe-center is always larger than that from optical measurement.
1987, 36 (11): 1485-1491. doi: 10.7498/aps.36.1485
The sulphur and oxygen segregation on V(100) surface is investigated in detail by AES and LEED. The relation between S and O segregation is clearly demonstrated and two new surface reconstructions, (8×1)-O and (4×l)-O,on V(100) surface are disclosed. Various superstructures on this surface under different conditions of S & O segregation are studied systematically and the relationship among these surface structures is obtained.
1987, 36 (11): 1492-1495. doi: 10.7498/aps.36.1492
The refractive indices of unpolarized KIO3 crystal in three different directions have been measured in the range of visible wavelength. The existence of type I phase matching surface in KIO3 crystal has been verified by experimental method. The optimum phase matching direc-tion in unpolarized KIO3 crystal has been found.
The finite energy resolution of EXAFS spectrometer is an important effect on EXAFS measurement. It lowers the EXAFS amplitude and the decrement in smaller k is greater than that in larger k. That causes smaller coordination number and the relative mean square displacement obtained from EXAFS data. This paper proposes a method to calculate the effect of the resolution on the structural parameters extracted from EXAFS. Structural parameters of Ge and Ni, as examples, were measured and calculated with different resolutions and the results are consistent with each other. The manner of how the effect occurs is discussed and a method to correct the influence of the finite energy resolution is presented.
1987, 36 (11): 1503-1508. doi: 10.7498/aps.36.1503
Dielectric properties of one-dimensoional polymer PTS single crystal have been measured along the chain direction in the temperature rang 77-273 K. A second-order phase transition from a high temperature nonpolar state to a low temperature polar state accompanied by an anomaly in the dielectric constant is observed at 195 K. Two peaks in the dielectric loss are found at 150 K and 100 K. The results are explained by a model which invokes three modes of side group motions.
1987, 36 (11): 1509-1512. doi: 10.7498/aps.36.1509
Applying Landau's Fermi liquid theory, we explain the superconductive critical temperature change with pressure in UBe13. The conclusion is that UBe13 is a possible P-wave superconductor. Furthermore, we find the effect of f energy levels displacement relative to Fermi energy level and s-f hybridization increase due to applying pressure are of benefit to S-wave superconductors, but not of benefit to P-wave superconductor.
1987, 36 (11): 1513-1518. doi: 10.7498/aps.36.1513
We have studied (l+l)-dimensional gauge theory with the chiral fermions using the path-integral approach. Performing a non-abelian chiral change of variables and choosing a more general regularization operator, we get the exact solution of the fermion determinant. We also show that there can exist a mass generation in the theory for the vector bosons. Apart from a mass term, the solution contains a gauged Wess-Zumino-Witten anomaly functional and some other non-local terms.
1987, 36 (11): 1519-1525. doi: 10.7498/aps.36.1519
The formula of the elastic scattering amplitude in the Glauber theory are re-derived. If we take rectanguler optic potential as zero order approximation and Woods-Saxon optical potential as exact potential, we find that the partial integral can be performed further in the original scattering amplitude formulas. Finally, We obtain the revised scattering amplitude without angle constraint.
1987, 36 (11): 1526-1528. doi: 10.7498/aps.36.1526
In this paper, a new type of quantum mechanical amplifier using transition beat is described. At room temperature, as the bandwidth of receiver is 2 KHz, the sensitivity is 5×10-15 W.