Table of Content

20 August 1998, Volume 7 Issue 8 Previous Issue    Next Issue

ATOMIC AND MOLECULAR PHYSICS

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ENERGY AND LIFETIME OF CORE-EXCITED Be+ RESONANCES Gou Bing-cong, Deng Wen-sheng, Zhang Jian-ping 1998, 7 (8):  561-566.  doi: 10.1088/1004-423X/7/8/001 Abstract ( 0 )   PDF (214KB) ([an error occurred while processing this directive])   The energies, shifts, widths, and radiative rates of double excited Be+ resonances are calculated using the saddle point and saddle-point complex-rotation methods. A restricted variational method is used to extrapolate a better nonrelativistic energy. Relativistic effects are included using first-order perturbation theory. These results are used to make a better understanding of observed Be+ spectra.

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TWO PHOTONS EXCITED 4d RYDBERG STATE OF AsH3 Ran Qin, Pei Lin-sen, Wang Fei, Chen Yang, Chen Cong-xiang, Yu Shu-qin, Ma Xing-xiao 1998, 7 (8):  567-571.  doi: 10.1088/1004-423X/7/8/002 Abstract ( 0 )   PDF (191KB) ([an error occurred while processing this directive])   In this paper, by using resonance enhanced (2+1) multiphoton ionization (REMPI) of AsH3 and detecting the daughter molecular ions AsH+ and As+, a long progression discrete structure was obtained from 267 to 291 nm, which obeys the formula ν0(cm-1)=68875.3+504.1v′2+5.26v′22. Analysis of the spectrum has revealed that it belongs to 4d Rydberg state transition. Our assignment yields the 4d Rydberg state parameters Te′=67881.1 cm-1, ωe′=495.1 cm-1 and δ=0.962. Finally the 4d Rydberg state structure of AsH3 was discussed.

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OPTICAL ISOTOPE SHIFTS AND CONFIGURATION MIXING AT THE LEVEL (26772)011/2 IN Nd II Ma Hong-liang, Shi Wei, Chen Miao-hua, Chen Zhi-jun, Fang Du-fei, Lu Fu-quan, Yang Fu-jia 1998, 7 (8):  572-575.  doi: 10.1088/1004-423X/7/8/003 Abstract ( 0 )   PDF (182KB) ([an error occurred while processing this directive])   Optical isotope shifts in the transition 4f45d 6I11/2-(26772)011/2 of Nd II were measured by using collinear fast-ion-beam laser spectroscopy. The configuration admixtures of the previously unclassified (26772)011/2 level were quantitatively analyzed to be 4f46p, 4f35d2, and 4f35d6s with mixing probabilities of 13%, 85%, 2%, respectively.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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FORMATING DOUBLE LAYER MECHANISM BY ELECTRIC CHARGED PARTICLE STREAM IN PLASMA Ma Shan-jun, Yang Qian-li, Li Xiao-qing 1998, 7 (8):  576-582.  doi: 10.1088/1004-423X/7/8/004 Abstract ( 0 )   PDF (204KB) ([an error occurred while processing this directive])   In this paper, two-fluid equations have been solved after having considered magnetic field generated by charged particle stream. Finally, the distribution of electric field Ez(z,r) and its growth rate γ in plasma have been obtained. From the expression of Ez(z,r) it can be known that the double layer has been formed. With the increase of disturbance γ will be larger, and finally this will result in the interruption of electric current and occurrence of burst.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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MOLECULAR DYNAMICS SIMULATION ON LOW ANGLE GRAIN BOUNDARIES Li Bin, Zhang Xiu-mu, Li Yi-yi 1998, 7 (8):  583-588.  doi: 10.1088/1004-423X/7/8/005 Abstract ( 0 )   PDF (216KB) ([an error occurred while processing this directive])   Molecular dynamics simulation has been performed to investigate the microstructure and properties of low angle grain boundaries, employing the embedded atom method(EAM) type interatomic potential for Ni-Al alloy. The energies of the low angle grain boundaries with different dislocation densities were calculated, and the results indicate that the low angle grain boundary energy varies as a function of misorientation angle. The simulation was found in good agreement with the calculation on the basis of the dislocation theories in the low angle scale. The low angle grain boundary energy goes up with the increase of misorientation angle and tends to go down after reaching a maximum. An energy cusp exists when the misorientation angle increases further, but in this scale the dislocation theories are invalid for energy calculation due to the strong interaction of the dislocations at the boundaries. The simulation results also indicate that the microstructure of low angle grain boundaries can still be described as dislocations when the misorientation angle is larger than 10°.

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THE ANNEALING EFFECT OF CRYSTAL 4H-SiC FILMS PREPARED BY PULSED LASER DEPOSITION Wang Yu-xia, Wen Jun, Tang Ye-qing, Guo Zhen, Tang Hong-gao, Wu Jian-xin 1998, 7 (8):  589-597.  doi: 10.1088/1004-423X/7/8/006 Abstract ( 0 )   PDF (216KB) ([an error occurred while processing this directive])   SiC films were prepared by pulsed XeCl laser ablation of ceramic SiC target on Si(100) substrate at temperature 850℃ and post-deposition high temperature annealing above 1100℃ (1100℃-7 Pa). The surface morphology, crystal structure, composition and chemical state of the element in the films before and after annealing were studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Auger electron Spectrum, X-ray photoelectron spectrum and photoluminescence methods. It was found that the films were consisted of polycrystal 4H-SiC structure before annealing and were turned into singlecrystal epitaxial 4H-SiC after annealing. The surfaces of the films were smooth and the adhesion of films with the substrate was good. The films were transparent. Excited by the laser with wavelength 290 nm at room temperature, the films emitted two luminescence bands with the peaks at 377 nm and 560 nm. The emission at 377 nm was attributed to the combination of the transmission among the valence and conductor bands, while the one at 560 nm was possibly to be from exciton emission.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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AN EFFECTIVE APPROACH FOR TWO-DIMENSIONAL POLARONS IN AN ASYMMETRIC QUANTUM DOT Ren Yu-hang, Chen Qing-hu, Jiao Zheng-kuan 1998, 7 (8):  598-607.  doi: 10.1088/1004-423X/7/8/007 Abstract ( 0 )   PDF (269KB) ([an error occurred while processing this directive])   Within the framework of Feynman-Haken path integral theory, we calculate the ground-state energy of two-dimensional polarons in asymmetric quantum dots for arbitrary electron-phonon coupling constants. From a general three-dimensional Hamiltonian, some interesting problems, such as polarons in quasi-one-dimensional quantum wires and quasi-zero-dimensional asymmetric or symmetric quantum dots can be easily discussed only by taking different limit in the whole coupling regime. After the numerical calculation, we find that the relative polaronic correction increases monotonically with the decrease of effective dot size, and it becomes more pronounced with increasing dimension and asymmetry. Moreover, despite the insensitivity of relative polaronic enhancement to the variation of coupling constant at weak coupling, the correction is related to the coupling constant as the latter becomes larger.

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PHOTOLUMINESCENCE AND RAMAN SCATTERING OF PURE GERMANIUM/SILICON SHORT PERIOD SUPERLATTICE Ji Zhen-guo, Norikata Usami, H. Sunamura, Yasuhiro Shiraki 1998, 7 (8):  608-612.  doi: 10.1088/1004-423X/7/8/008 Abstract ( 0 )   PDF (179KB) ([an error occurred while processing this directive])   Pure Ge/Si short period superlattice (SPS) samples grown by gas source molecular beam epitaxy (GS-MBE) were studied by photoluminescence and Raman scattering. For SPS samples with Germanium layer thickness (LGe) of 1.5 monolayer (ML), a new band of photoluminescence is observed for silicon layer thickness (LSi) in an intermediate range of 1.9-2.9 nm. In contrast to pure Ge/Si quantum wells, the energy of the new band shows a red-shift with the increase of LSi. Raman scattering results show that when the intensity of the photoluminescence of the new band reaches a maximum, the Raman shift relating the vibration of Si-Si reaches a minimum. It is therefore considered that the new band of the pure Ge/Si SPS is related with some kind of strain relaxation process.

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OSCILLATORY INTERLAYER COUPLING WITH Cu AND Zr UNDERLAYER THICKNESS FOR Co/Cu MULTILAYERS Zhao Tong-yun, Shan Zheng-sheng, Shen Bao-gen, Zhao Jian-gao, D. J. Sellmyer 1998, 7 (8):  613-617.  doi: 10.1088/1004-423X/7/8/009 Abstract ( 0 )   PDF (198KB) ([an error occurred while processing this directive])   Oscillatory behavior (with a period of about 9 nm) of antiferromagnetic coupling with the thicknesses of Cu and Zr underlayers is reported for sputtered Co(1 nm)/Cu(2.3 nm) multilayers. The related oscillation of magnetoresistance is also observed. Based on the analysis of X-ray diffraction patterns, the variation of crystallographic orientation and modulation period is proved not responsible to the phenomenon. But the underlayer strongly affects the growth orientation of multilayer.

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COLORATION EFFECT OF PULSED LASER ON WO3 Zhao Yan, Feng Zhong-chao, Liang Yong 1998, 7 (8):  618-622.  doi: 10.1088/1004-423X/7/8/010 Abstract ( 0 )   PDF (153KB) ([an error occurred while processing this directive])   When laser pulses irradiate the surface of the sample WO3, an interesting coloration effect is obtained. Only by one pulse of XeCl laser irradiation (wavelength: 308 nm, pulse duration: 36 ns, output power: 100 mJ/pulse), a significant color change appears. X-ray photoelectron spectroscopy (XPS) shows that a partial reduction process of WO3 occurs and conduction band electrons appears. X-ray diffraction pattern indicates that the lattice parameters of the colored samples are increased. A molten layer can be seen in scanning electron microscopy (SEM) image. It may be concluded that the coloration effect of pulsed laser undergoes a process different from that of electro- or photo- chromism, and may be attributed to thermochromism and substoichiometric WO3 is formed. The coloration process is characterized by its high speed and stability.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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LASER MOLECULAR BEAM EPITAXY SYSTEM AND ITS KEY TECHNOLOGIES Yang Guo-zhen, Lü Hui-bin, Zhou Yue-liang, Lei Zhen-lin, Chen Zheng-hao 1998, 7 (8):  623-627.  doi: 10.1088/1004-423X/7/8/011 Abstract ( 0 )   PDF (177KB) ([an error occurred while processing this directive])   The laser molecular beam epitaxy system and its key technologies have been successfully developed in China. Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 (STO) and heteroepitaxial BaTiO3 (BTO) films and STO/BTO superlattices were fabricated on STO (100) substrates by the laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles of undamping intensity oscillation were obtained by using in-situ reflection high-energy electron diffraction. The surfaces of films are atomically smooth.