Papers by Author: Jung Goo Lee

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Authors: Takuro Nakamura, Hiromoto Kitahara, Jung Goo Lee, Nobuhiro Tsuji
Abstract: Pure Al (99%) and pure Fe (99.5%) sheets were mutually stacked and severely deformed up to equivalent strain of 16 by the accumulative roll bonding (ARB) process in an attempt to achieve bulk mechanical alloying. The deformation was carried out at RT. The Al/Fe sheets ARB processed by 1 cycle showed a number of shear bands penetrating the stacked layers. The Fe layers, which were harder than the Al layers, were subdivided by the shear bands into diamond-shaped regions. Dissolution of Fe into Al was observed and a supersaturated solid solution was formed in the specimen ARB processed by 10 cycles. It was also found that local amorphization occurred at interface regions via formation of Al5Fe2 intermetallic compound.
Authors: Hidehiro Yasuda, A. Tanaka, H. Usui, Hirotaro Mori, Jung Goo Lee
Abstract: The effect of electron dose rate on phase separation induced by electronic excitation in GaSb nanoparticles has been studied in order to see whether a nonlinear relation between density of excited states introduced and the efficiency of the phase separation is found or not. The phase separation to two phases consisting of an antimony core and a gallium shell proceeds after incubation time with increasing electron dose and does only at the dose rate above a threshold value. It is suggested that such nonlinear behaviors take place as a cooperative phenomenon among electronic-excitation effect, nano-size effect and temperature.
Authors: Jung Goo Lee, Ryusuke Nakamura, Daisuke Tokozakura, Hideo Nakajima, Hirotaro Mori, Jong Hoon Lee
Abstract: The formation of hollow zinc oxide has been studied by oxidation and subsequent thermal treatment of nanometer-sized zinc particles using in-situ TEM. The zinc particles produced under UHV condition were exposed to air at room temperature for 0.6 ks, which resulted in the formation of oxide layer with thickness of 3 nm. Subsequent heating inside UHV chamber of TEM induced the evaporation of the inner zinc, which resulted in the formation of hollow zinc oxide. The produced hollow zinc oxide had the wurtzite structure. Based upon the vapor pressure of the inner zinc, it seems reasonable to consider that the internal zinc vapor leaks away through the interface between the oxide layer and the amorphous carbon film used as a supporting substrate.
Authors: Ryusuke Nakamura, Jung Goo Lee, Daisuke Tokozakura, Hirotaro Mori, Hideo Nakajima
Abstract: Formation of hollow structure through oxidation of Al nanoparticles was studied by applying transmission electron microscopy. Al nanoparticles 6~8 nm in diameter were observed to become hollow particles after having been exposed to air at 295 K for a few minutes. An analysis of the Debye-Sherrer rings in the selected area diffraction patterns before and after oxidation showed that hollow oxide nanoparticles are amorphous. The formation mechanisms of hollow oxide are discussed based on the low-temperature oxidation mechanism of Al and on the comparison with our previous results of hollow ZnO formation via oxidation of Zn nanoparticles.
Authors: Kyeong Sik Cho, Hghn Joon Choi, Jung Goo Lee, Yung Woo Park
Authors: Yung Woo Park, J.Y. Kim, Mamoru Mitomo, G.D. Zhan, Jung Goo Lee
Authors: Jung Goo Lee, Hirotaro Mori
Abstract: TEM is one of the most powerful experimental tools for the study of nanometer-sized particles. In the present work, the finite size effect on both the stability of two-phase microstructure and the solid solubility has been examined by in situ TEM using particles in the Au-Ge system. The size effect on the two-phase microstructure is rather small when the size of particles is larger than approximately 10 nm in diameter. However, the effect becomes strong in particles smaller than about 10 nm in diameter and an amorphous structure appears instead of the crystalline two-phase microstructure. The solid solubility in each solid solution in nanometer-sized alloy particles with a two-phase microstructure gradually increased as the particle size decreased. The enhancement of solid solubility was large in gold solid solution as compared with the in germanium solid solution.
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