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Sim, Gi-dong

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Sim

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Gi-dong

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Sim, Gi-dong
Author's Publications: search.filters.isAuthorOfPublication.f1261397-3694-43d8-b3d0-d06b8e8325e7

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    An Apparatus for Performing Microtensile Tests at Elevated Temperatures inside a Scanning Electron Microscope
    (Elsevier, 2013) Sim, Gi-dong; Park, Jun-Hyub; Uchic, Michael D.; Shade, Paul A.; Lee, Soon-Bok; Vlassak, Joost
    In this paper, we introduce an apparatus to perform microtensile tests at elevated temperatures inside a scanning electron microscope. The apparatus has a stroke of 250 μm with a displacement resolution of 10 nm and a load resolution of 9.7 μN. Measurements at elevated temperatures are performed through use of two silicon-based micromachined heaters that support the sample. Each heater consists of a tungsten heating element that also serves as a temperature gauge. To demonstrate the testing capabilities, tensile tests were performed on submicron Cu films at various temperatures up to 430 °C. Stress–strain curves show a significant decrease in yield strength and initial slope for the samples tested at elevated temperature, which we attribute to diffusion-facilitated grain boundary sliding and dislocation climb.
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    Scanning AC Nanocalorimetry Study of Zr/B Reactive Multilayers
    (American Institute of Physics, 2013) Lee, Dongwoo; Sim, Gi-dong; Xiao, Kechao; Seok Choi, Yong; Vlassak, Joost
    The reaction of Zr/B multilayers with a 50 nm modulation period has been studied using scanning AC nanocalorimetry at a heating rate of approximately \(10^3 K/s\). We describe a data reduction algorithm to determine the rate of heat released from the multilayer. Two different exothermic peaks are identified in the nanocalorimetry signal: a shallow peak at low temperature (200–650°C) and a sharp peak at elevated temperature (650–800°C). TEM observation shows that the first peak corresponds to heterogeneous inter-diffusion and amorphization of Zr and B while the second peak is due to the crystallization of the amorphous Zr/B alloy to form \(ZrB_2\).
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    High-temperature tensile behavior of freestanding Au thin films
    (Elsevier BV, 2014) Sim, Gi-dong; Vlassak, Joost
    The mechanical behavior of freestanding thin sputter-deposited films of Au is studied at temperatures up to 340 °C, using tensile testing. Films tested at elevated temperatures exhibit a significant decrease in flow stress and stiffness. Furthermore, the flow stress decreases with decreasing film thickness, contravening the usual notion that “smaller is stronger”. This behavior is attributed mainly to diffusion-facilitated grain boundary sliding.