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Role of Cluster Geometry in Evolution of Electronic Structures of Small Aluminum Clusters
ZHAI Hua-jin, ZHAO Ji-jun, NI Guo-quan, ZHOU Ru-fang, WANG Guang-hou, WANG Yu-zhu
Chin. Phys. Lett. 1997, 14 (12):
897-900
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The electronic structures of small aluminum clusters, Aln (n = 5 - 24), are investigated by a localized-orbital theory based on the tight-binding approximation. Magic-numbered clusters each exhibit a HOMO-LUMO gap maximum, and simultaneously an s-p gap minimum, but not necessarily an ionization potential maximum, where HOMO-LUMO gap denotes the energy gap between the highest occupied orbital and the lowest unoccupied orbital of the cluster. Also revealed is an irregular odd-even alternation in HOMO-LUMO gaps for Aln (n = 7-24). Cluster geometry either contributes to or dominates these findings.
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A New Wall Conditioning Technique Developed on the HT-7 Superconducting Tokamak with a Permanent Magnetic Field
ZHAO Yan-ping, LI Jian-gang, XIE Ji-kang, MENG Yue-dong, WU Xin-chao, HE Ye-xi, XUE Di-ye, DENG Xu, SHAO Yu-gui
Chin. Phys. Lett. 1997, 14 (12):
916-919
.
A new technique for wall conditioning with a permanent magnetic field has been tested and developed on the HT-7 superconducting tokamak by ion cyclotron range frequency wave injection. The operation ranges for conditioning and recycling was investigated with different working gas (D2, He), toroidal field (0.1-2.5 T) and rf powers. The experimental results show that its cleaning efficiency is about three times higher than that of glow discharge cleaning. This new technique has been used daily during experiments.
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Elastic Behaviors of Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 Investigated by Using Ultrasonic Technique
WANG Ru-ju, QIN Zhi-cheng, LI Feng-ying, XIE Hong-sen
Chin. Phys. Lett. 1997, 14 (12):
920-923
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The acoustic velocity, attenuation, and their pressure dependence of a bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 have been measured under pressures up to 0.5 GPa at room temperature using the pulse echo overlap method. The sample was prepared from melt by quenching into liquid nitrogen. Bulk modulus, Young’s modulus, shear modulus, and Poisson’s ratio were derived, other elastic properties and vibrational anharmonicity were also discussed.
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Oxygen-Diffusion and Structural Modification in Air-Annealed Superconducting Bi2Sr2CaCu2Oy Single Crystals
ZHAO Xiao-ru, WU Wen-bin, SUN Xue-feng, WANG Liang-bin, ZHOU Gui-en, LI Xiao-Guang, ZHANG Yu-heng, Koichi Kitazawa
Chin. Phys. Lett. 1997, 14 (12):
936-939
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Bi2Sr2CaCu2Oy single crystals were air-annealed at 300, 400, 600 and 750°C for 20h in consequence. Measurements of ac susceptibility and x-ray diffraction showed that at annealing temperature below 400°C, the change of Tc was dominated by oxygen-diffusion involved in pervoskite unit and was strongly sample-dependent. This diffusion from pervoskite unit occurred earlier than that from Bi-O layers. At annealing temperature over 400°C, with the intercalation of excess oxygen into Bi-O layers, the hole concentration in the crystal was redistributed so that Bi-O reservoir fully determined superconductivity. From the changes of non-uniform strain in annealing process, it was found that structural modification was also closely correlated to superconductivity.
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Low Field-Induced Electron Emission Phenomenon Observed from the Carbon Containing Thin Films
CHEN Jun, WEI Ai-xiang, ZHANG Hai-yan, LU Yong, ZHENG Xin-guo, MO Dang, PENG Shao-qi, XU Ning-sheng
Chin. Phys. Lett. 1997, 14 (12):
949-952
.
Stable cold-cathode electron emission at fields as low as 3 MV/m has been observed from two types of carbon-containing thin film of thickness in submicron scale, i. e., non-doped fullerene C60 and amorphous diamond films. A transparent anode imaging technique was used to record the spatial distribution of individual sites and the total emission current-voltage characteristic of the films. It is found that supplemental measurements of optical spectra and electrical conductivity of the films can provide important evidence useful for understanding the differences in emission behaviour between two types of film.
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21 articles
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