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Ungyu Paik,Sangkyu Lee,Jea-Gun Park 대한전자공학회 2008 Journal of semiconductor technology and science Vol.8 No.1
The effect of physicochemical properties of solvents on the microstructure of polyvinyl carbazole (PVK) film for non-volatile polymer memory was investigated. For the solubilization of PVK molecules and the preparation of PVK films, four solvents with different physicochemical properties of the Hildebrand solubility parameter and vapor pressure were considered: chloroform, tetrahydrofuran (THF), 1,1,2,2-tetrachloroethane (TCE), and N,N-dimehtylformamide (DMF). The solubility of PVK molecules in the solvents was observed by ultraviolet-visible spectroscopy. PVK molecules were observed to be more soluble in chloroform, with a low Hildebrand solubility parameter, than solvents with higher values. The aggregated size and micro-/nano-topographical properties of PVK films were characterized using optical and atomic force microscopes. The PVK film cast from chloroform exhibited enhanced surface roughness compared to that from TCE and DMF. It was also confirmed that the microstructure of PVK film has an effect on the performance of non-volatile polymer memory.
UnGyu Han,Jinho Ahn 보안공학연구지원센터 2015 International Journal of Software Engineering and Vol.9 No.2
Typically, the previous load balancing methods for Flume which completely depends on the user-specified threshold does not adaptively deal with the performance change of the entire log processing system at runtime. Furthermore, their task-transferring algorithm aggravates the performance degradation of the overloaded node because the excessive data transfer to another node should be done on the overloaded node. In this paper, we propose a new load balancing method for Apache Flume by automatically and dynamically modifying threshold of node load status in accordance with the runtime performance of the system. This feature can be realized by monitoring both the increasing rate of incoming log information in the queue of each collector agent and its occupancy rate at the request of the overloaded or under-loaded collection node in a decentralized manner. The proposed method considerably alleviates the additional overhead incurred by the task migration and makes the load of the entire system as fair as possible by selecting the optimal task migration destination depending on the current load-state values of collector agents unlike the previous round-robin and random ones.
Wavy polymer thin film fabrication using sintered monolayered colloids.
Yi, Dong Kee,Paik, Ungyu American Scientific Publishers 2010 Journal of nanoscience and nanotechnology Vol.10 No.8
<P>Thin films of polystyrene were prepared onto flexible prestrained substrates using a convective colloidal assembly in monolayer fashion followed by thermal annealing at 150, and 160 degrees C. The prestrained substrate was under a tensile stress which was subsequently released resulting in wavy polymer thin films. By controlling the prestrain, the released stress was varied and the geometry of the resulting wavy patterns was tuned. Wavelength and amplitude values showed strong correlation with theoretical expectations. In addition to the uniaxial mechanical strain, thermal strain was also present in the experimental conditions; however, the resulting wavy patterns show no evidence of being affected by the isotropic thermal strain in our experimental model.</P>
Song, Dowon,Paik, Ungyu,Guo, Xingye,Zhang, Jing,Woo, Ta-Kwan,Lu, Zhe,Jung, Sung-Hoon,Lee, Je-Hyun,Jung, Yeon-Gil Elsevier 2016 Surface & coatings technology Vol.308 No.-
<P><B>Abstract</B></P> <P>The effects of microstructure design on the lifetime performance of lanthanum zirconate (La<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB>; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal durability in La<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB> based TBCs has been investigated. </LI> <LI> Cyclic thermal exposure tests were employed in determining thermal durability. </LI> <LI> Buffer layer can improve the thermal durability of TBC in fast cooling rates. </LI> <LI> Blended composition can enhance the thermal durability of TBC in slow cooling rates. </LI> <LI> TBC with a double buffer layer showed the most outstanding thermal durability in all tests. </LI> </UL> </P>
Nature of Surface and Bulk Defects Induced by Epitaxial Growth in Epitaxial Layer Transfer Wafers
Suk-Goo Kim,박재근,Ungyu Paik 한국전기전자재료학회 2004 Transactions on Electrical and Electronic Material Vol.5 No.4
Surface defects and bulk defects on SOI wafers are studied. Two new metrologies have been proposed to characterize surface and bulk defects in epitaxial layer transfer (ELTRAN) wafers. They included the following: i) laser scattering particle counter and coordinated atomic force microscopy (AFM) and Cu-decoration for defect isolation and ii) cross-sectional transmission electron microscope (TEM) foil preparation using focused ion beam (FIB) and TEM investigation for defect morphology observation. The size of defect is 7.29 um by AFM analysis, the density of defect is 0.36 /cm2 at as-direct surface oxide defect (DSOD), 2.52 /cm2 at ox-DSOD. A hole was formed locally without either the silicon or the buried oxide layer (Square Defect) in surface defect. Most of surface defects in ELTRAN wafers originate from particle on the porous silicon.
박재근,박금석,강현구,Manabu Kanemoto,Ungyu Paik 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3
Effects of the triethanolamine (TEA) concentration in a ceria slurry on the removal rates and the removal selectivity of SiO2 and Si3N4 films were investigated by performing shallow trench isolation chemical mechanical polishing (STI-CMP). At a higher concentration of TEA in the polishing slurry, the removal rate of the Si3N4 film significantly decreased while maintaining a high removal rate of the SiO2 film with a high removal selectivity of the SiO2-to-Si3N4 films during the CMP process. We found that the adsorption behavior between TEA and the surface of the Si3N4 film was determined by the electrokinetic behavior, where the zeta-potential measurement depended on the suspension's pH. Adsorption results demonstrated that as the TEA concentration was increased, the force of attraction between negatively charged hydroxyl groups along the backbone of the TEA and the surface of the Si3N4 film was enhanced due to an electrostatic attraction force. Through these reactions, the zeta potential of the Si3N4 film's surface became more positive because of the amine functional group of TEA in the slurry. In addition, with increasing zeta potential of the Si3N4 film, a denser passivation layer was formed on the Si3N4 film with an anionic surfactant, which led to suppression of the removal of the Si3N4 film with a higher SiO2-to-Si3N4 removal selectivity in the STI CMP.