Papers by Author: Jae Hak Choi

Abstract: Nanocomposite materials based on poly(p-hydroxystyrene-co-2-methyl-2-adamantyl methacrylate-co-methacrylisobutyl-POSS) were synthesized and evaluated as EUV chemically amplified resists. Incorporation of 2-methyl-2-adamantyl and POSS groups into the matrix polymer made it possible to improve the dry-etch resistance, and excellent lithographic performance was obtained. The well-defined 250 nm positive patterns were obtained using a KrF excimer laser scanner, and 100 nm elbow patterns using an EUV lithography tool. The dry-etch resistance of this resist for a CF4-based plasma was comparable to that of poly(p-hydroxystyrene).

Abstract: Silicon (Si) nanoparticles were stabilized by sodium dodecyl sulfate and poly(Nvinylpyrrolidone) in water, and coated with polypyrrole (PPy) via an in-situ polymerization of pyrrole with FeCl3. TEM images revealed that the Si nanoparticles were successfully coated with PPy (average thickness, ~2 nm). The Li/PPy-coated Si electrode exhibited improved discharge capacities, when compared to that of a reported Li/pure Si electrode. PPy-coatings on the Si nanoparticles acted as efficient conducting agents and prevented an extraction of the cracked Si fragments into the electrolyte to some extent.

Abstract: Polystyrene-grafted γ-Al2O3 nanoparticles were successfully synthesized by a high energy irradiation technique. Surface modification of the nanoparticles with silane coupling agents was performed to introduce active sites on the γ-Al2O3 nanoparticles for a radiation-induced graft polymerization. The polymer graft yield increased with the absorbed dose. The graft yield was higher at a 50 vol% monomer solution than at 70 vol%.

Abstract: Ethyl-cellulose (EC) nanofibers were fabricated by an electrospinning of an EC solution with a 6-12 wt% concentration. Fiber morphology was observed under a scanning electron microscope and the effects of instrument parameters including the solution concentration, flow rate and electric voltage were investigated.

Abstract: Nano- to micro-structured biodegradable poly(ε-caprolactone) nanofibrous scaffolds (PCL NFSs) were prepared by an electrospinning. Electrospinning has recently emerged as a leading technique for generating the biomimetic scaffolds for tissue engineering applications. The average diameter of the electrospun PCL NFSs ranged from 0.5 to 2 ㎛ depending on the solvent/nonsolvent mixture. PCL NFSs were irradiated using γ-ray and their mechanical properties and biodegradability were measured. In vitro/vivo degradation studies of the scaffolds as a function of the radiation dose were performed. The scaffolds were degraded more slowly in vitro than in vivo.