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- 저자 : 이상현(S.H. Lee) (검색결과 104 건)
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AFM을 이용한 Si (001) 표면에 Ge 나노점의 형성과 성장과정에 관한 연구
박정식,이상현,최명섭,송덕수,이성수,곽동욱,김도형,양우철,Park, J.S.,Lee, S.H.,Choia, M.S.,Song, D.S.,Leec, S.S.,Kwak, D.W.,Kim, D.H.,Yang, W.C. 한국진공학회 2008 Applied Science and Convergence Technology Vol.17 No.3
The nucleation and evolution process of Ge nano-islands on Si(001) surfaces grown by chemical vapor deposition have been explored using atomic force microscopy (AFM). The Ge nano-islands are grown by exposing the substrates to a mixture of gasses GeH4 and H2 at pressure of 0.1-0.5Torr and temperatures of $600-650^{\circ}C$. The effect of growth conditions such as temperature, Ge thickness, annealing time on the shape, size, number density, and surface distribution was investigated. For Ge deposition greater than ${\sim}5$ monolayer (ML) with a growth rate of ${\sim}0.1ML/sec$ at $600^{\circ}C$, we observed island nucleation on the surface indicating the transition from strained layer to island structure. Further deposition of Ge led to shape transition from initial pyramid and hut to dome and superdome structure. The lateral average size of the islands increased from ${\sim}20nm$ to ${\sim}310nm$ while the number density decreased from $4{\times}10^{18}$ to $5{\times}10^8cm^{-2}$ during the shape transition process. In contrast, for the samples grown at a relatively higher temperature of $650^{\circ}C$ the morphology of the islands showed that the dome shape is dominant over the pyramid shape. The further deposition of Ge led to transition from the dome to the superdome shape. The evolution of shape, size, and surface distribution is related to energy minimization of the islands and surface diffusion of Ge adatoms. In particular, we found that the initially nucleated islands did not grow through long-range interaction between whole islands on the surface but via local interaction between the neighbor islands by investigation of the inter-islands distance.
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이상현(S. H. Lee),곽호상(H. S. Kwak),한창수(C. S. Han),류도현(D. H. Ryu) 한국전산유체공학회 2003 한국전산유체공학회지 Vol.8 No.4
This study presents a numerical model to analyze dynamic thennal behavior of a hot chuck designed for flip-chip bonders. The hot chuck of concern is a heater which has been specifically developed for accomplishing high-speed and ultra-precision soldering. The characteristic features are radiative heat source and the heating tool made of a material of high thermal diffusivity. A physical modeling has been conducted for the network of heat transport. A simplified finite volume model is deviced to simulate time-dependent thermal behavior of the heating too on which soldering is achieved. The reliability of the proposed numerical model is verified experimentally. A series of numerical tests illustrate the usefulness of the numerical model in design analysis.
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이상현(S. H. Lee),김경섭(K. S. Kim),주용규(Y. K. Ju),김종호(J. H. Kim) 한국소성가공학회 2015 금형가공 심포지엄 Vol.2015 No.8
Restriking is a kind of sizing process which is an additional operation for increasing the accuracy of the shape or dimension of a cup formed from the previous step. In this paper, Restriking is limited to make a corner sharp of a cup in the last step. A new stepped punch is designed for this experiment. Experiments were carried out to investigate which condition prevented the occurrence of concave defect on the bottom of cylindrical cups as well as which condition gave the minimum corner radius of a cylindrical cup in the restriking process.
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