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Search for the Halo Effect in the 1H(6He, 6Li)n Reaction
LI Zhi-Hong, LIU Wei-Ping, BAI Xi-Xiang, WANG You-Bao, LIAN Gang, LI Zhi-Chang, SHEN Qing-Biao, LIN Cheng-Jian, ZENG Sheng, FU Chang-Bo
Chin. Phys. Lett. 2002, 19 (3):
306-308
.
The angular distributions of the charge exchange reaction 1H(6He, 6Li)n were measured in reverse kinematics with a secondary 6He beam at the energy of 4.17 A MeV. The data were analysed in the context of a microscopic calculation. It is shown that both the ground state of 6He and the second excited state of 6Li (3.563MeV, 0+) have a halo structure.
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Giant Neutron Halo in Exotic Calcium Nuclei
ZHANG Shuang-Quan, , MENG Jie, , ZHOU Shan-Gui, , ZENG Jin-Yan,
Chin. Phys. Lett. 2002, 19 (3):
312-314
.
The properties of even-even Ca isotopes are studied using the
relativistic continuum Hartree-Bogoliubov theory. The calculations reproduce very wwell the experimental binding energies E and two neutron separation energies S2n. The predicted neutron drip nuclei is 72Ca. From the analysis of S2n, the neutron radii and neutron density distribution, giant neutron haloes are predicted in Ca isotopes with A > 60.
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Atomic Magnetic Lattices and Their Applications
YIN Jian-Ping, GAO Wei-Jian, HU Jian-Jun, LIU Nan-Chun
Chin. Phys. Lett. 2002, 19 (3):
327-330
.
We propose a novel scheme to construct one-, two- or three-dimensional (1D, 2D or 3D) atomic magnetic lattices by using various arrays of microscopic magnetic traps, which are composed of some arrays of current-carrying wires. The magnetic field distributions from 1D, 2D and 3D arrays of the current-carrying wires are calculated, and some interesting and periodic magnetic microstructures are found. Our study shows that these magnetic lattices may be used to prepare 1D, 2D or 3D photonic crystals and so on.
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Performance of the Self-Q-Switched Cr,Yb:YAG Laser
DONG Jun, DENG Pei-Zhen, LIU Yu-Pu, ZHANG Ying-Hua, HUANG Guo-Song, GAN Fu-Xi
Chin. Phys. Lett. 2002, 19 (3):
342-344
.
We report on the spectral properties of Cr,Yb:YAG crystal co-doped with 0.025 at.% Cr and 10 at.% Yb are reported. Using a continuous wave Ti:sapphire laser as a pumping source, We have demonstrated the self-Q-switched Cr,Yb:YAG laser has been at room temperature. We obtained an average output power as much as 75mW at 1.03μm with a pulse width (FWHM) as short as 0.4 μs. The laser experiment demonstrated that the Cr,Yb:YAG crystal exactly combines the Cr4+ saturable absorber and Yb3+ gain medium. The Cr,Yb:YAG crystal can be a most promising self-Q-switched laser crystal for compact and efficient solid-state lasers.
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High Gain Lateral Semi-Insulating GaAs Photoconductive Switch Triggered by 1064 nm Laser Pulses
SHI Wei, ZHANG Xian-Bin, LI Qi, CHEN Er-Zhu, ZHAO Wei
Chin. Phys. Lett. 2002, 19 (3):
351-354
.
We report on the experimental results of a lateral semi-insulating GaAs photoconductive switch, with a gap of 8mm between two electrodes, triggered by 1064nm laser pulses at the wavelength beyond the GaAs absorption edge. Both the linear and nonlinear modes of the switch were observed when it was triggered by light pulses with energy of 1.9mJ and the pulse width of 60ns, and operated at high voltage of 3 and 5kV. The results show that when the semi-insulating GaAs photoconductive switch operates under an electrical field of 4.37kV/cm, it will enter into the linear mode first, and then the switch will undergo the nonlinear mode (lock-on) after a delay of about 20-100ns. It is worth noticing that the delay time under high light energy is longer than that in the low optical energy. The non-intrinsic absorption mechanism is discussed. EL2 deep level defects and double-photon absorption in GaAs may play a key part in the absorption process.
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Microstructures of GaN Films Laterally Overgrown on Si(111) by Hydride Vapor Phase Epitaxy
CHEN Zhi-Zhong, ZHANG Rong, ZHU Jian-Min, QIN Zhi-Xin, SHEN Bo,
GU Shu-Lin, WANG Feng, ZHENG You-Dou, ZHANG Guo-Yi, LI Zhi-Feng, L. F. KUECH
Chin. Phys. Lett. 2002, 19 (3):
375-377
.
We have investigated the microstructures of GaN films laterally epitaxially overgrown (LEO) on Si (111) substrates by hydride vapor phase epitaxy. The threading dislocation density in the LEO GaN is reduced by about two orders. Different etching angles of the two sidewalls of SiO2 masks (66°and 90°) lead to the asymmetry of the LEO and cause the particular microstructures of LEO GaN. In micro-Raman spectra, the intensities vary weakly periodically about 5μm perpendicular to the mask stripes. The indistinction selective growth in the top surface is discussed.
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Grain Boundary Peak in a Foamed Zn-Al Eutectoid Alloy
WEI Jian-Ning, CHENG He-Fa, GONG Chen-Li, ZHOU Zheng-Cun,
LI Zhi-Bin, HAN Fu-Sheng
Chin. Phys. Lett. 2002, 19 (3):
381-384
.
We study experimentally the temperature spectra of internal friction (IF) and relative dynamic modulus (RDM) in a foamed Zn-Al eutectoid alloy. The specimens with macroscopic pores (0.5--1.0mm) were prepared in an air pressure infiltration process. The damping behaviour of the foamed Zn-Al eutectoid alloy is characterized by IF. The IF and RDM measurements at maximum surface shear strain of 20 x 10-6 have been made by using a multifunction internal friction apparatus at frequencies of 0.5, 1.0, and 3.0 Hz from room temperature to equilibrium eutectoid isotherm of 277°C, while continuously changing the temperature cycle. At low frequency, an IF peak is observed in the IF-temperature curve. The IF peak is of a grain boundary, which is associated with the diffusive flux on a crystalline boundary between the like-phases of Al/Al. Its activation energy has been calculated to be 1.10±0.06eV and the pre-exponential factor τ0 is 10-14s in the IF measurements.
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Microstructural Models of Alumina Nanotubes and Anodic Porous Alumina Film Formed in Sulfuric Acid
PU Lin, CHEN Zhi-Qiang, TAN Chao, YANG Zheng, ZOU Jian-Ping, BAO Xi-Mao, FENG Duan, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2002, 19 (3):
391-394
.
Electrochemical stepwise-anodization of aluminum in dilute sulfuric acid results in the formation of alumina nanotubes (ANTs) which is due to hexagonal split of anodic porous alumina (APA) film along the cell boundaries containing many voids, that is, the ANTs are the completely detached cell of the APA film. The inner diameters of the ANTs are in the range of 10-20nm, and the aspect ratio (inner diameter/length) of the ANTs can be about 80. The relations found for pore diameter, cell diameter and barrier layer thickness are around 1, 2.7 and 0.85 nm/V, respectively. Transmission electron microscope (TEM) reveals that the ANT wall has a three-shell structure: an outer shell (metal/oxide interface) consisting of pure alumina oxide, a middle shell of the hydrated oxide or/and hydroxide and an inner shell (oxide/electrolyte interface) of anion incorporated oxide with the thickness ratio of 1:1:2. The structural change of ANTs induced by e-beam irradiation in TEM indicates that the thermal instability of the hydrated oxide or/and hydroxide within the cell wall might be an alternative origin contributing to the self-organization of the cells, leading to a densely packed triangular cell lattice of the APA film.
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Dependence of Tunnel Resistance on the Injection Current of Magnetic Tunnel Junctions
LIU Cun-Ye, LI Jian, CHEN Jian-Yong, XU Qing-Yu, NI Gang, DU You-Wei
Chin. Phys. Lett. 2002, 19 (3):
398-401
.
Anomalous transport behaviour, i.e., the dependence of the tunnel resistance on the injection current, has been discovered in Ta/Co/Al2O3/FeNi tunnel junctions. The zero field voltage-current characteristic of the magnetic tunneling junction obeys the transport principle of the normal tunnel junction at low injection current, but it exhibits the negative resistance behaviour when the injection current is raised to the breakover current level. The physics of the restorable electric breakdown has been initially studied.
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Atomic and Electronic Structures of Submonolayer In on Cu(111)
WANG Peng, XUN Kun, JIA Jin-Feng, GAO Xing, QIAN Hai-Jie, LIU Feng-Qin, Ibrahim Kurash, ZHOU Yu-Mei, XUE Qi-Kun, WU Si-Cheng
Chin. Phys. Lett. 2002, 19 (3):
409-412
.
We have studied the atomic and electronic structures of submonolayer In on Cu(111) using synchrotron radiation photoemission and scanning tunnelling microscopy (STM). At very low coverage, In atoms were favorable to occupy substitutional sites and to be distributed evenly on Cu(111) surface. At higher coverage of 0.33 and 0.50 ML, two ordered reconstructure phases of (√3 x√3)R30°and (2 x 1) have been observed for the first time. The two dimensional states of In induced valence bands in the (√3 x√3)R30°phase were measured by angle-resovled photoemission. The result is in good agreement with theoretical calculations.
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Behaviour of Oxygen-Implanted and Hydrogen-Implanted SiGe/Si Heterostructure
AN Zheng-Hua, ZHANG Miao, MEN Chuan-Ling, SHEN Qin-Wo, LIN Zi-Xin, LI Kai-Cheng, LIN Cheng-Lu
Chin. Phys. Lett. 2002, 19 (3):
413-415
.
For SiGe-on-insulator fabrication, a 100nm SiGe film with uniform germanium composition was grown on Si (100) substrate using a molecular beam epitaxy system without a graded SiGe buffer layer. The samples were implanted by oxygen ions at an energy of 45 keV and a dose of 3 x 1017cm-2, and annealed for five hours at 1250°C in flowing (Ar + 5% O2) atmosphere with a 100 nm oxide protective layer. The result indicates that a buried oxide layer was successfully formed at the interface of SiGe and Si on the substrate. Furthermore, hydrogen was implanted into SiGe at the energy of 62 keV and the dose of 6 x 1016cm-2 to perform a blistering study, which confirmed the feasibility of H-induced layer splitting in SiGe layer.
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Interface Instability of Diamond Crystals at High Temperature
and High Pressure
YIN Long-Wei, LI Mu-Sen, XU Bin, CUI Jian-Jun, HAO Zhao-Yin
Chin. Phys. Lett. 2002, 19 (3):
419-421
.
Diamond growth instability at high temperature and high pressure (HPHT) has been elucidated by observing the cellular interface in diamond crystals. The HPHT diamond crystals grow layer by layer from solution of carbon in the molten catalyst. In the growth of any other crystals from solution, the growth interface is not stable and should be of the greatest significance further to understand the diamond growth
mechanism. During the diamond growth, the carbon atoms are delivered to the growing diamond crystal by diffusion through a diamond crystal-solution boundary layer. In front of the boundary layer, there exists a narrow constitutional supercooling zone related to the solubility difference between diamond and graphite in the molten catalyst. The diamond growth stability is broken, and the flat or planar growth interface transforms into cellular interface due to the light supercooling. The phenomenon of solute trails in the diamonds was observed, the formation of solute trails was closely associated with the cellular interface.
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Physical Properties of Diamond Coatings on a WC-6%Co Substrate
LIU Sha, YI Dan-Qing, YU Zhi-Ming
Chin. Phys. Lett. 2002, 19 (3):
422-424
.
We have investigated the physical properties, including the morphology, texture, adhesion and chemical quality, of high-frequency chemical vapour deposited diamond coatings on WC-6%Co substrates which were pre-treated by a two-step etching method. The results indicate that the increasing Co content from 0.12 to 3.05% within the etching depth of 5μm caused a morphology transformation from prism diamond to spherulitic diamond, and a texture one from a {111} orientation to a {110} orientation. The Raman spectrum shows that the spherulitic diamond film contains more non-diamond phases (graphite, amorphous carbon and diamond-like carbon, etc) and has lower chemical quality of diamond films on a WC-6%Co substrate. The diamond coating grain sizes became smaller about 4 times when the deposition temperatures on the substrate surface were reduced from 1000 to 900°C. Compared with spherulitic diamond films, the prism diamond films exhibit better adhesion on the WC-6%Co substrate.
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48 articles
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