Papers by Author: Young Chang Joo

Abstract: The distribution of the precipitates on the grain boundaries in Fe-3%Si steel during secondary recrystallization annealing were studied using high-angle annular dark filed (HAADF) scanning transmission electron microscopy (STEM). Because HAADF image can show both grain boundaries and precipitates clearly, the change of precipitate distribution on grain boundaries can be quantitatively analyzed. It was observed that the total area of the precipitates on grain boundaries increased in the order of non-annealed, 600°C, and 900°C sample and the total area of precipitates on grain boundaries in the 1000 °C sample was much lower than that in the 900 °C sample. The compositions of the precipitates were also analyzed using X-ray energy-dispersive spectrometer (XEDS). The most precipitates were multi-phase ones, mainly composed of AlN and MnS. Our analysis results suggest that such a precipitate behavior is responsible for the abnormal grain growth of Fe-3%Si steel occurring under the temperature above 900 °C.

Abstract: Use of silver (Ag) nanoparticle suspension for various applications such as ink-jet printing of electronic circuits has been of prime interest. We observed the microstructure evolution of the inkjet-printed Ag thin films on Si substrates under various annealing conditions using the field-emission scanning electron microscopy (FE-SEM). Abnormal grain growth characteristics were identified when annealed at about 240 oC under ambient air. Growth characteristics of pores were found to be in accordance with that of grains. Competition between grain and pore growth is attributed to small grain sizes, low packing density and high porosity, which are characteristic of inkjet-printed Ag films as dried.

Abstract: In-situ observation by scanning electron microscope of the microstructure evolution near the cathode depletion region and the quantitative analysis on the number of hillock phases in the eutectic SnPb edge drift structure made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb, respectively, under 50 oC while both dominant migrating element and dominant hillock phase were Pb above 100 oC. Such temperature-dependence of the dominant hillock phases in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions.

Abstract: Hillocks were observed in various thick Al films after annealing for a long time and their density and diameter were measured using an image analysis program. The hillock density decreased while the diameter increased with increasing film thickness. The total hillock volume per unit area of the film is linearly proportional to the film thickness and annealing temperature. Based on the results of our investigation, the effect of the film thickness, grain size and annealing temperature on hillock formation is discussed, and an equation that can be used to predict the hillock density and average hillock diameter is suggested.

Abstract: The reaction induced phase separation aimed for the distribution of nano-structured particles has been investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) in ternary Ti-Si-N film via N+ implantation. The fabrication of Ti-20at%Si film has made on Si substrates by ion beam sputtering (IBS), and then N+ implantation with 50 keV has been conducted on these films. The selected area electron diffraction (SAED) from as-deposited film shows amorphous Ti-Si. As-deposited Ti-Si film exhibited high stability even for the heat treatment at 773K for 3600s. N+ implantation induced the direct formation of nano crystalline of fcc-TiNx within the Ti-Si film. The XPS depth profiling and chemical shift suggest that the preferential nitriding of Ti accompanied with the segregation of SiNx occurred during N-implantation.