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Chin. Phys. B  
  Chin. Phys. B--1993, Vol.2, No.9
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NUCLEAR PHYSICS

THE STUDIES OF NON-RUTHERFORD BACKSCATTERING CROSS SECTIONS OF 4He FROM 16O

CHENG HUAN-SHENG, SHEN HAO, TANG JIA-YONG, YANG FU-JIA
Chin. Phys. B 1993, 2 (9): 0641;  doi: 10.1088/1004-423X/2/9/001
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In this article, we report the 170° backscattering cross sections of 4He from 16O in the energy range of 2.0-9.0 MeV. Our measurements show that the alpha-oxygen scattering remains Rutherford scattering up to Eα=2.35 MeV, and there exist two energy regions, namely 5.55-5.85MeV and 8.50-8.80MeV, where the cross sections are enhanced and show a smooth variation. The measured laboratory cross sections are 9.50-9.97 and 35.0-33.0 times greater than the Rutherford values, respectively. In the 8.50-8.80MeV region, the cross sections at scattering angles of 160°, 165°, 170° and 175° were measured and found to be strongly angle-dependent. A most strong resonance occurred at 7.60 MeV, where the cross section is 200 times of its Rutherford value. This resonance has been used to measure the 16O concentration on a Cu surface, with a sensitivity of 1×1015 oxygen atoms/cm2, Besides, we have studied the backscattering angle dependence of the threshold energy, i.e., the energy at which the elastic cross section begins to deviate from its Rutherford value. The experimental result seems not in agreement with the prediction made from the analytical formula developed by Bozoian et al.
ATOMIC AND MOLECULAR PHYSICS

ELECTRON-ELECTRON CORRELATION IN THE HELIUM 3De DOUBLY EXCITED STATES

DUAN YI-WU, BAO CHENG-GUANG
Chin. Phys. B 1993, 2 (9): 0648;  doi: 10.1088/1004-423X/2/9/002
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The qualitative features of the electron-electron correlation in the helium 3De doubly excited states have been investigated via an example of the N = 3, n=4 series. The angular, radial-angular and radial-radial correlations have been shown in detail and the anisotropism of the electronic cloud has been found. The features of the 3De states have been compared with those of the L≤1 states.
CLASSICAL AREAS OF PHENOMENOLOGY

ANISOTROPIC INFRARED-UP-CONVERSION LUMINESCENCE GENERATION IN POROUS SILICON

WANG JIAN, JIANG HONG-BING, WANG WEN-CHENG, ZHENG JIA-BIAO, ZHANG FU-LONG, HAO PING-HAI, HOU XIAO-YUAN, WANG XUN
Chin. Phys. B 1993, 2 (9): 0658;  doi: 10.1088/1004-423X/2/9/003
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It is demonstrated in this paper that the infrared-up-conversion luminescence generation from porous silicon, considered as an enhanced third-order nonlinear optical effect by the recent work, is anisotropic as the polarization vector of normally incident fundamental light is rotated. A new method has been used to determine the anisotropy parameter σ of the third-order nonlinear optical tensor χ(3). Due to the sensitivity of σ to the crystal structure and microscopic electronic properties, the difference in σ′s between porous and crystalline silicon, particularly in their phases, demonstrates that the nanometer structure of porous silicon induces a dra-matic change of the electronic band structure, but the strongly anisotropic crystal property remains unchanged.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

STRONG-COUPLING SURFACE OPTICAL POLARON IN A MAGNETIC FIELD

CHEN CHUAN-YU
Chin. Phys. B 1993, 2 (9): 0664;  doi: 10.1088/1004-423X/2/9/004
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A variational scheme of the Pekar type is employed to study the strong-coupling optical polaron on the outer surface of the polar crystal under the influence of a magnetic field. The ground state energy and the effective mass of the polaron are obtained as functions of the magnetic field strength and the electron-surface optical phonon coupling constant. It is shown that the effective mass of the surface polaron appears in nonisotropic nature due to the coupling between the electron and the surface optical phonon.

Ge BEAM TREATMENT OF Si SUBSTRATE FOR MOLECULAR BEAM EPITAXY

CUI QIAN, LU XUE-KUN, WEI XING, YANG XIAO-PING, GONG DA-WEI, Lü HONG-QIANG, SHENG CHI, ZHANG XIANG-JIU, WANG XUN
Chin. Phys. B 1993, 2 (9): 0671;  doi: 10.1088/1004-423X/2/9/005
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A new surface cleaning method for Si MBE is described in which a very weak Ge beam flux is deposited on the surface for removing the thin passivative layer of SiO2 on the Si subetrate. It has proved that the SiO2 will react with Ge at a relatively low temperature (620℃), and as a result, the oxide layer becomes volatile. Here the high temperature annealing in the conventional Shiraki method is no longer required, and since the oxide layer is removed in ultra high vacuum, only very little carbon contamination may occur. Furthermore, to reduce the excessive Ge on the substrate surface, Ge is deposited at 620℃ and then the sample is annealed at 700℃; the residual Ge atoms on Si substrate can be reduced to less than 0.1 monolay-er (ML). Ge beam treatment turns out to be an effective low-temperature Si surface-cleaning method, especially for the heteroepitaxial growth of GexSi1-x/Si.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

INFLUENCE OF OXYGEN UPON THE SUPERCONDUCTIVITY OF THE Pb-DOPED 2223 SUPERCONDUCTOR

CHEN TING-GUO, SHEN ZNONG-ZHE, XIE XIAO-MING, CHEN YUAN
Chin. Phys. B 1993, 2 (9): 0678;  doi: 10.1088/1004-423X/2/9/006
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The influences of oxygen content (by quenching from different temperatures in air or oxygen) and its re-distribution (by annealing in nitrogen at 200℃) on Tc and room temperature resistivity were studied. It was found that Tc as a function of oxygen content or charge carrier concentration exhibits a maximum. Upon oxygen re-distribution, the room temperature resistivity would always inclose but Tc would change in a complicated way. Tc increases for the oxygen-rich state and decreases for the oxygen-deficient state Internal friction measurements showed that there are two kinds of oxygen defects in the Bi2-O2 layers. One is the isolated oxygen interstitials and the other is oxygen vacancies on the excess oxygen chains. It is proposed that the isolated interstitial oxygen will produce a set of impurity states near the Fermi level, and will create holes on the Cu3d-O2p band through charge transfer from the Cu3d-O2p band to the impurity states. The content of the isolated oxygen interstitial is believed to be the major factor for determining the charge carrier concentration. Variation of Tc and room temperature resistivity with oxygen re-distribution is sat-isfactorily explained as to be induced by combination of oxygen interstitials with oxygen vacancies on the excess oxygen-chains.

MAGNETO-OPTICAL EFFECT IN Co-BASED METALLIC LAYERED AND MULTILAYER FILMS

LUO CHUN-PING, WANG YING-JUN
Chin. Phys. B 1993, 2 (9): 0688;  doi: 10.1088/1004-423X/2/9/007
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A preliminary investigation of the magneto-optical effect in Co-based metallic bilayer, trilayer and multilayer films has been carried out in this paper. Various sublayers of non-magnetic materials with different thicknesses were selected. The Kerr enhancement due to the reduction of effective optical constants in Co/Ag bilayers and multilayers has been achieved.

THE ULTRAVIOLET UP-CONVERSION LUMINESCENCE OF NONCRYSTALLINE ErP5O14

CHEN XIAO-BO, ZHANG GUANG-YIN, CHEN JIN-KAI, WANG HONG, LIU YAN-BIN, SHANG MEI-RU, LI JIANG-WEI
Chin. Phys. B 1993, 2 (9): 0695;  doi: 10.1088/1004-423X/2/9/008
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This paper reports the observation of the ultraviolet up-conversion lumines-cence phenomenon of noncrystalline ErP5O14 excited by pulse 532nm laser. The up-conversion mechanism is explained as follows, namely, when noncrystalline ErP5O14 is excited by 532nm laser, the excited population is mainly deposited in 4S3/2 level because of the strong nonradiative relaxation between 2H11/2 and 4S3/2 level, then up-converted to (2H2G)9/2 level by energy transfer between Er3+ ions, this produces the ultraviolet luminescence.

INVESTIGATION OF ION SPUTTERING FOR EUTECTIC Cu-37 at% Ag ALLOY

WANG ZHEN-XIA, PAN JI-SHENG, ZHANG JI-PING, TAO ZHEN-LAN, ZHU FU-YING, ZHAO LIE, ZHANG HUI-MING
Chin. Phys. B 1993, 2 (9): 0702;  doi: 10.1088/1004-423X/2/9/009
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Angular distribution of sputtered atoms and the phenomenon of "element local richness relative to microtopographic feature" (ELR-MTF) of the sputtered tar-get surface have been investigated on Cu-37at%Ag alloys by means of Rutherford backscattering spectroscopy technique and a method based on combined scanning electron microscopy and electron probe microanalysis measurements. In this paper, emphasis is put on the bombardment with different doses and angular distributions of sputtered atoms ejecting from various micro-zones on the topographic surface during sputtering. We propose a new model (ELR-MTF model) to interpret the shape of angular distributions and the variation of R-θ (ejection angle of sputtered atoms) curves. This model can qualitatively explain the experiment quite well.
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