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Choi, Jaeho,Cho, Wonhee,Jung, Yeon Sik,Kang, Hong Suk,Kim, Hee-Tak American Chemical Society 2017 ACS NANO Vol.11 No.2
<P>Anisotropic movement of azobenzene materials (i.e., azobenzene molecules incorporated in polymer, glass, or supramolecules) has provided significant opportunities for the fabrication of micro/nanoarchitectures. The examples include circular holes, line gaps, ellipsoidal holes, and nanofunnels. However, all of the previous studies have only focused on the lateral directional movement for the structural shaping of azobenzene materials. Herein, we propose structural shaping based on a vertical directional movement of azobenzene materials. To do this, light with oblique incidence, containing normal direction light polarization, was illuminated onto azobenzene materials film contact with patterned elastomeric molds (i.e., PDMS) so that the resulting vertical directional movement of azobenzene materials fills in the cavities of the molds and results in pattern formation. As a result, a range of patterns with sizes of features from micro- to sub-100 nm scale was successfully fabricated in a large area (few cm(2)), and the structural height was deterministically controlled by simply adjusting irradiation time. In addition to the notable capability of fabricating the single-scale structures, the technique provides a facile way to fabricate complex hierarchical multiscale structures, ensuring its versatility and wide applicability to various applications. As a selected exemplary application of the multiscale structures, a superhydrophobic surface has been successfully demonstrated.</P>
Choi, Jaeho,Le, Quyet Van,Hong, Kootak,Moon, Cheon Woo,Han, Ji Su,Kwon, Ki Chang,Cha, Pil-Ryung,Kwon, Yongwoo,Kim, Soo Young,Jang, Ho Won American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36
<P>It was demonstrated that organolead halide perovskites (OHPs) show a resistive switching behavior with an ultralow electric field of a few kilovolts per centimeter. However, a slow switching time and relatively short endurance remain major obstacles for the realization of the next generation memory. Here, we report a performance-enhanced OHP resistive switching device. To fabricate topologically and electronically improved OHP thin films, we added hydroiodic acid solution (for an additive) in the precursor solution of the OHP. With drastically improved morphology such as small grain size, low peak-to-valley depth, and precise thickness, the OHP thin films showed an excellent performance as insulating layers in Ag/CH3NH3PbI3/Pt cells, with an endurance of over 103 cycles, a high on/off ratio of 10(6), and an operation speed of 640 mu s and without electroforming. We suggest plausible resistive switching and conduction mechanisms with current voltage characteristics measured at various temperatures and with different top electrodes and device structures. Beyond the extended endurance, highly flexible resistive switching devices with a minimum bending radius of 5 mm create opportunities for use in flexible and wearable electronic devices.</P>
Choi, Jaeho,Jo, Wonhee,Lee, Seung Yeol,Jung, Yeon Sik,Kim, Shin-Hyun,Kim, Hee-Tak American Chemical Society 2017 ACS NANO Vol.11 No.8
<P>Springtails, insects which breathe through their skins, possess mushroom-shaped nanostructures. As doubly re-entrant geometry, in the mushroom-head enhances the resistance against liquid invasion, the springtails have robust, liquid-free omniphobic skins. Although omniphobic surfaces are promising for various applications, it remains an important challenge to mimic the structural feature of springtails. This paper presents a pragniatic method to create doubly re-entrant nanostructures and robust superomniphobic surfaces by exploiting localized photofluidization of azopolymers. Irradiation of circularly polarized light reconfigures azopolymer micropillars to have a mushroom-like head with a doubly re-entrant nanogeometry through protrusion and inward bending of polymer film from the top edge. The light-driven reconfigured micropillars facilitate the pining of triple line as springtails do. In particular, the unique geometry exhibits superomniphobicity even for liquids whose equilibrium contact angles are almost zero in the presence of a practical level of external pressure. In addition, the simple fabrication process is highly reproducible, scalable, and compatible with various substrate materials including flexible polymeric film. Our results suggest that our photofluidization technology will provide a practical route to develop robust superomniphobic surfaces.</P>
A Three-dimensional Modeling of Microscale Thin-film Initiator with Boron/titanium Multilayers
Jaeho Choi,Kyoungjin Kim 한국추진공학회 2020 Journal of Propulsion and Energy Vol.1 No.1
A novel integration attempt of nanoscale bimetallic multilayers into microscale thin-film explosive initiator has been proposed to improve initiator ignition performance. In order to study the ignition behaviors of boron (B) and titanium (Ti) multilayers by RC initiation circuit and bridge ohmic heating, this investigation introduced a three-dimensional computational model that includes thermal and atomic species diffusion in B/Ti multilayers as well as electric potential analysis in thin-film initiator coupled with RC circuit equation. Computational results found significant three-dimensional effects by spatially non-uniform bridge ohmic heating and lateral bridge heat loss. B/Ti reaction ignition and propagation proceeds quite differently from previous one-dimensional approximation model. More realistic present model predicts longer delay of bimetallic reaction ignition and much higher electrical energy requirement, when compared to existing one-dimensional model.
Choi, Jeongeun,Choi, Myung-Ja,Kim, Choonmi,Cho, Young-Shik,Chin, Jaeho,Jo, Young-Ah The Pharmaceutical Society of Korea 1997 Archives of Pharmacal Research Vol.20 No.1
To obtain more sensitive immunoassay for methamphetamine (MA) determination, the optimum condition of enzyme-linked immunosorbent assay (ELISA) was investigated in regard to immunogens, antibody purification methods and coating tracers. Activated MA, N-(4-aminobutyl)methamphetamine (4-ABMA), was conjugated with bovine serum albumin (BSA) or keyhole limpet hemocyanin (KLH) and used as immunogen. The antibodies were purified by protein G chromatography or various immunoaffinity chromatography-linked MA-protein ligands, such as MA-BSA, MA-KLH or MA-ovalbumin (OVA). Each purified antibody was characterized by means of sensitivity and cross-reactivity using the three MA-protein coating tracers, MA-BSA, MA-KLH and MA-OVA. The best sensitivity of each antibody was acquired with the MA-OVA tracer although the tracer concentration and the antibody titer level at optimum condition were varied. The antibody with high titer level did not always yield good sensitivity. At optimum condition, immunoaffinity chromatography-purified antibodies were better for sensitivity and for specificity than protein G-purified antibodies. The cross-reactivity of the purified antibodies seemed to be affected by immunogen structure and showed somewhat different patterns according to the immunoaffinity ligand utilized. These data show that the antibody purification method as well as choice of coating tracer and immunogen is essential for the sensitivity and specificity of EIA; the optimum condition for assay should be discovered using various methods and combinations.