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Distorted Wave Effects of the 1b3g Orbital in Ethylene
DENG Jing-Kang, LI Gui-Qin, HUANG Jian-Dong, WANG Fang, NING Chuan-Gang, LU Jie, HE Yao, WANG Xiao-Dong, ZHANG Yi-An, Gao Hong, WANG Yan, ZHENG Yan-You
Chin. Phys. Lett. 2002, 19 (1):
47-49
.
We study the unexpected distorted wave effects of the 1b3g orbital in ethylene using a high resolution binary (e, 2e) electron momentum spectrometer, at an impact energy of 800eV plus the binding energy (8-22eV) with symmetric non-coplanar kinematics. The experimental momentum profile of the 1b3g orbital is obtained and compared with the data previously measured at impact energy of 1200 eV plus the binding energy. Also, the experimental momentum profiles of the 1b3g orbital are compared with the theoretical momentum distributions calculated by using Hartree-Fock and density functional theory methods. The experimental momentum profiles of the 1b3g orbital of ethylene at different impact energies show that the cross section of the orbital below the momentum p~1 a.u. is higher for lower impact energy.
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Manakov Soliton Pairs in Biased Photovoltaic Photorefractive
Crystals
HOU Chun-Feng, DU Chun-Guang, Abdurusul, LI Shi-Qun
Chin. Phys. Lett. 2002, 19 (1):
63-65
.
We study, theoretically, incoherently coupled screening-photovoltaic soliton pairs in biased photovoltaic photorefractive crystals. It is shown that when the total intensity of two coupled solitons is much lower than the effective dark irradiance, the coupled soliton equations reduce to the Manakov equations. The dark-dark, bright-bright, and dark-bright soliton pair solutions of these Manakov equations are obtained under an appropriate external bias field and a photovoltaic field, and the characteristics of these Manakov soliton pairs are also discussed in detail.
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Wavelength Dependence of a Two-Beam Coupling Measurement on a
Fully Functional Photorefractive Polymer
ZHANG Bo, LIU Hui, GONG Qi-Huang, Jiwon Sohn, Jaehoon Hwang, Soo Young Park, Jin-Kyung Lee, Jai-Hyung Lee, Joon-Sung Chang, Geon Joon Lee
Chin. Phys. Lett. 2002, 19 (1):
66-68
.
We have investigated the photorefractive properties of a fully functional polymer, 9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H carbazole, using a multiline He-Ne laser. We measured the wavelength-dependent two-beam coupling coefficient, which exhibited a maximal value of 105 cm-1 at 609 nm under an applied electric field of 84 V/μm at room temperature.
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Synthesis of Large Quantity Single-Walled Carbon Nanotubes by Arc-Discharge
LI Zhen-Hua, WANG Miao, WANG Xin-Qing, ZHU Hai-Bin, LU Huan-Ming, Y. Ando
Chin. Phys. Lett. 2002, 19 (1):
91-93
.
We reported on a new method to prepare large quantity single-walled carbon nanotubes (SWCNTs) with high purity. Using a Y-Ni powder composite graphite rod as anode, at a given angle with the high purity graphite cathode rod, a cloth-like deposit can be obtained by dc arc discharge in helium at high temperature, which contained about 60% SWCNTs. In this way, we can obtain a deposit of more than one gram in ten minutes. Transmission electron microscopy and Raman spectrum have been used to observe the structure and morphology of the SWCNTs.
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Range and Annealing Behaviour of Pb+ Ion-Implanted into LiNbO3 Crystals at Moderate Energies
CHEN Feng, HU Hui, ZHANG Jian-Hua, LIU Xiang-Dong, XIA Hui-Hao, SHI Bo-Rong, WANG Ke-Ming
Chin. Phys. Lett. 2002, 19 (1):
101-104
.
Pb+ ions have been implanted into LiNbO3 crystals in the energy range of 100-350keV at doses of 5 x 1015, 1 x 1016 and 2 x 1016 ions/cm2. The profile of the implanted ions was measured by Rutherford backscattering. The mean projected range and the range straggling obtained from the experiment were compared with the TRIM'98 and SRIM 2000 code. In the present case, the TRIM'98 code predicts experimental values better than those of the SRIM 2000 code. The depth distribution is also found to be independent of dose for 350-keV Pb+ implanted into LiNbO3 crystals. After 800°C annealing for 60 min in ambient air, obvious diffusion occurs to the implanted Pb+ ions at 150 keV with a dose of 5 x 1015 ions/cm2. After a low-temperature treatment at 77 K in liquid nitrogen, no obvious diffusion phenomenon occurs for the implanted Pb+ ions in LiNbO3.
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Binding Energy of Positively and Negatively Charged Excitons
in GaAs/AlxGa1-xAs Quantum Wells
LIU Jian-Jun, , ZHANG Shu-Fang, YANG Guo-Chen, LI Shu-Shen
Chin. Phys. Lett. 2002, 19 (1):
114-116
.
Using a simple two-parameter wavefunction, we calculate variationally the binding energy of positively and negatively charged excitons in GaAs/AlxGa1-xAs quantum wells for the well widths from 10 to 300Å, We consider the effect of effective mass, dielectric constant mismatch in the two materials, and the whole correlation among the particles. The results are discussed and compared in detail with previous experimental and theoretical results, which show a fair agreement with them.
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Electron States of Few-Electron Quantum Dots
DAI Zhen-Hong, , SUN Jin-Zuo, ZHANG Li-De, LI Zuo-Hong, HUANG Shi-Yong, SUI Peng-Fei,
Chin. Phys. Lett. 2002, 19 (1):
117-119
.
We study few-electron semiconductor quantum dots using the unrestricted Hartree-Fock-Roothaan method based on the Gaussian Basis. Our emphasis is on the energy level calculation for quantum dots. The confinement potential in a quantum dot is assumed to be in a form of three-dimensional spherical finite potential well. Some valuable results, such as the rearrangement of the energy level, have been obtained.
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Enhanced MgB2 Superconductivity Under High Pressure
LIU Zhen-Xing, JIN Chang-Qing, YOU Jiang-Yang, LI Shao-Chun, ZHU Jia-Lin, YU Ri-Cheng, LI Feng-Ying, WANG Ru-Ju, SU Shao-Kui
Chin. Phys. Lett. 2002, 19 (1):
120-123
.
We report on in situ high-pressure studies up to 1.0 GPa on the MgB2 superconductor which was high-pressure synthesized. The as-prepared sample is of high quality in terms of sharp superconducting transition (Tc) at 39 K from the magnetic measurements. The in situ high-pressure measurements were carried out using a Be-Cu piston-cylinder-type instrument with the mixed oil as the pressure transmitting medium which warrants a quasi-hydrostatic pressure environment at low temperature. The superconducting transitions were measured by using the electrical conductance method. It is found that Tc increases more than 1 K with pressure in the low-pressure range, before the Tc value decreases with the further increase of the pressure.
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A New Method for the Preparation of MgB2 Superconducting Tapes
XU Jia-Di, WANG Shu-Fang, ZHOU Yue-Liang, DAI Shou-Yu, CHEN Zheng-Hao, CUI Da-Fu, LÜ, Hui-Bin, ZHU Ya-Bin, HE Meng, YANG Guo-Zhen
Chin. Phys. Lett. 2002, 19 (1):
122-123
.
Superconducting MgB2/Ta tapes with critical temperature of 38 K have been prepared successfully by a two-step method. Boron/Ta tapes were fabricated by electrophoresis followed by a post-annealing process in magnesium vapour. The critical current density is 1.7 x 104A/cm2 in zero field at 5K. Scanning electron microscopy and x-ray diffraction analysis reveal a dense flat surface with (101) orientated growth of MgB2 phase in our MgB2/Ta tapes.
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Photoluminescence and Optically Pumped Ultraviolet Lasing from
Nanocrystalline ZnO Thin Films Prepared by Thermal Oxidation of High Quality ZnS Thin Films
ZHANG Xi-Tian, LIU Yi-Chun, ZHANG Li-Gong, ZHANG Ji-Ying, LÜ, You-Ming, SHEN De-Zhen, XU Wu, ZHONG Guo-Zhu, FAN Xi-Wu, KONG Xiang-Gui
Chin. Phys. Lett. 2002, 19 (1):
127-130
.
We present a simple and useful method for preparing high-quality nanocrystalline ZnO thin films, i.e. the thermal oxidation of high-quality ZnS films prepared by low-pressure metal-organic chemical vapor deposition technique. The x-ray diffraction measurements reveal that the nanocrystalline ZnO has a hexagonal wurtzite structure. Raman spectra show that the longitudinal optical phonon with the E1-mode appears at 578 cm-1. The multiple phonon scattering process is also observed, indicating the formation of a high quality nanocrystalline ZnO thin film. The photoluminescence spectrum has a single emission peak at 3.264 eV from the free-exciton mission, under the condition of low excitation power at room temperature. However, when excitation intensities exceed the threshold of 150 kW/cm2, a new and narrow peak emerges at lower energies, which are attributed to exciton-exciton collisions, and is called the P line. The intensity of this peak increases superlinearly with the pumping power over a threshold value. This supplies strong evidence of stimulated emission. The multiple longitudinal cavity modes observed in the stimulated emission spectrum indicate the successful realization of optically pumped lasing from nanocrystalline ZnO films at room temperature.
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Photoluminescence of ZnSe-ZnS Single Quantum Wells Grown by Vapor Phase Epitaxy
LÜ, You-Ming, SHEN De-Zhen, LIU Yi-Chun, LI Bing-Hui, ZHANG Ji-Ying, FAN Xi-Wu, S.Iida, A. Kato
Chin. Phys. Lett. 2002, 19 (1):
131-133
.
We study the photoluminescence (PL) of ultra thin layer ZnSe quantum wells in ZnS barriers. Samples with different well widths are grown by vapor phase epitaxy and the PL spectra of these samples are measured by the excitation of a 500 W Hg lamp. The peak positions of the bands coming from the excitonic luminescence show a larger blue shift with respect to the energy of free excitons in the ZnSe bulk material. The observed variation of the full width at half maximum and peak position of the bands in the spectra with the well width are interpreted to formation of the ZnSxSe1-x alloy layer due to the interdiffusion in the interfaces between ZnSe and ZnS. According to the behaviour of the excitons in the smaller conduction band offset, the exciton binding energy is estimated from the dependence of the PL intensity on the temperature. From this result, excitons seem to show nearly three-dimensional characteristics.
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45 articles
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