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Han H.-S.,Korea Institute of Science and TechnologySeoul | Park N.,Kookmin University | Suh J.-Y.,Korea Institute of Materials Science | Nam H.-S.,Kookmin University | And 4 more authors.
Intermetallics | Year: 2016

Glass forming ability (GFA) for some alloys may be difficult to explain in kinetic point of view alone and the thermodynamics must be considered as an important factor. Herein, investigation of the atomic size effect on the glass forming ability based on the molecular dynamics simulations for binary alloys with Lennard-Jones Embedded Atom Method potentials have been performed. The findings from this study showed that the size effect is accompanied by the change of phase diagram from solid solution to eutectic and change in the local stress/internal energy, which could contributes more to GFA than the kinetic factors such as efficient packing and resulting sluggish atomic transport. © 2015 Elsevier Ltd.

Ahn M.,Korea Institute of Science and Technology | Cha I.Y.,Korea Institute of Science and TechnologySeoul | Lee J.K.,Korea Institute of Science and Technology | Yoo S.J.,Korea Institute of Science and TechnologySeoul | And 2 more authors.
Journal of Materials Chemistry A | Year: 2015

Facile synthesis of Rh-Sn catalysts for the electrocatalytic oxidation of ethanol is carried out via a surfactant-free microwave-assisted method. The bifunctional mechanism and electronic modification with C-C bond splitting enable this electrocatalyst to be remarkably active and durable at high fuel concentrations, which allows for a significant reduction in the volume and weight of the fuel cell system. This journal is © The Royal Society of Chemistry.

Park J.H.,Korea Institute of Science and TechnologySeoul | Lee S.W.,Seoul National UniversitySeoul | Song D.S.,Seoul National UniversitySeoul | Jho J.Y.,Seoul National UniversitySeoul
ACS Applied Materials and Interfaces | Year: 2015

On purpose to enhance the generating force of ionic polymer-metal composite (IPMC) actuators, the thickness of the ion-exchange membrane is manipulated in two different ways. One is grafting poly(styrenesulfonic acid) onto poly(vinylidene fluoride-co-hexafluoropropylene) films with varying thickness, and the other is stacking pre-extruded Nafion films to thicker films by pressing at high temperatures. For both groups of the membranes, ionic properties including ion-exchange capacity and ionic conductivity are maintained similarly inside the groups regardless of the thickness. The actuation tests clearly show the increase in generating force with increasing thickness of the IPMCs prepared. It is due to a larger bending stiffness of thicker IPMCs, which is consistent with the predicted result from the cantilever beam model. The increase in force is more remarkable in Nafion-stacked IPMCs, and a thick IPMC lifts a weight of 100 g, which far exceeds the reported values for IPMCs. © 2015 American Chemical Society.

Yoon C.W.,Korea Institute of Science and TechnologySeoul | Jung Y.-G.,Korea Institute of Science and TechnologySeoul | Choi D.-K.,Korea Institute of Science and TechnologySeoul | Kim D.M.,Satellite Navigation Research Center | Nam S.W.,Korea Institute of Science and TechnologySeoul
EFC 2011 - Proceedings of the 4th European Fuel Cell Piero Lunghi Conference and Exhibition | Year: 2011

The ATR reactions of iso-octane were initially carried out with Rh-based catalysts (0.5 wt% of Rh) supported onto three kinds of supports, Al2O3, CeO2, and ZrO2. Observed activities were increased in the order of Rh/ Al2O3 > Rh/CeO2 > Rh/ZrO2. Stabilities against carbon coking of these catalysts, however, proved to be increased in the order of Rh/CeO2 > Rh/ZrO2 > Rh/- Al2O3. To derive synergic properties from each of - Al2O3 and CeO2 supports, a CeO2(20 wt%)/-Al2O3 supported Rh catalyst (0.5 wt% Rh) was synthesized and tested for the ATR reactions of iso-octane, showing enhanced activity and stability compared to those with Rh/ -Al2O3. The Rh/-Al2O3 and Rh/-Al2O3/CeO2 catalysts were eventually examined for the ATR reactions of commercial gasoline (GS Caltex, Korea) which contained sulfur, aromatics, and other impurities that could potentially deactivate the catalysts. It turned out that the Rh/-Al2O3 catalyst was significantly deactivated to decrease its activity after 4 h, while the Rh/-Al2O3/CeO2 catalyst proved to be excellent in terms of stability and activity.

Park J.,Chung - Ang University | Park J.,Korea Institute of Science and TechnologySeoul | Kim S.,Chung - Ang University | Sim Y.,Chung - Ang University | And 7 more authors.
Journal of Alloys and Compounds | Year: 2016

CdS nanowires were synthesized using a simple synthesis process using Au nanoparticles (average diameter: 13 nm) as catalyst. The growth conditions were optimized by varying the substrate temperature and the growth time of a thermal chemical-vapor-deposition system. CdS nanowires were successfully grown at temperatures above 480 °C. In fact, high-quality nanowires, with hexagonal wurtzite structures and an average diameter of 25 nm and length of 1.46 μm, were obtained after a 30-min synthesis at a growth temperature of 520 °C. Electron microscope images revealed that our CdS nanowires, grown at relatively lower growth temperatures, have higher average-aspect-ratio and smaller average-diameter than those previously reported in the literature. Our synthesis method resulted in CdS nanowires only without producing nanorods and nanobelts, which make it unnecessary to filter and purify nanowires from the mixture of nanowires, nanorods, and nanobelts. © 2015 Elsevier B.V.

Park J.K.,Korea Institute of Science and TechnologySeoul | Park J.K.,Korea Atomic Energy Research Institute | Lee G.Y.,Korea Institute of Science and TechnologySeoul | Jung K.,Korea Institute of Science and TechnologySeoul | And 3 more authors.
Nanoscale | Year: 2015

The triplet-triplet annihilation (TTA) efficiency in bicomponent organic systems is investigated by employing a gap plasmon resonator. In our structure, strong absorption peaks arising from coupling between localized surface plasmons and surface plasmon polaritons closely overlap the Q band of porphyrin, leading to higher triplet concentrations within the film. We find that at ultralow excitation intensities on the order of watts per square centimeter (W cm-2), TTA becomes predominant for the organic system on a gap plasmon resonator. A strong surface-enhanced Raman scattering intensity is observed in this substrate, verifying the near-field enhancement. This journal is © The Royal Society of Chemistry.

Chang H.J.,Korea Institute of Science and TechnologySeoul | Cho H.Y.,Korea Institute of Science and TechnologySeoul | Kim J.H.,Hanbat National University
Journal of Alloys and Compounds | Year: 2015

The microstructural stability of Y-Ti-O nanoparticles during spot laser beam melting of oxide dispersion-strengthened steel powder is investigated. After the spot laser beam melting, Y2Ti2O7 oxide nanoparticles are successfully retained without dissolution or transformation. However, their particle size is considerably coarser than typical Y2Ti2O7 nanoparticles due to the active agglomeration of the Y-Ti-O nanoparticles, Cr-carbides, and Ar bubbles. In particular, an unexpectedly large volume of Ar bubbles embedded or attached to the Y2Ti2O7 nanoparticles is observed. The Ar gas bubbles seem to accelerate the particle agglomeration. No other phase is observed than Y2Ti2O7 oxide, Cr-carbide and Ar bubble in the sample. © 2015 Elsevier B.V.

Pyo J.B.,Korea Institute of Science and TechnologySeoul | Kim B.S.,Korea Institute of Science and TechnologySeoul | Kim B.S.,Chung - Ang University | Park H.,Korea Institute of Materials Science | And 7 more authors.
Nanoscale | Year: 2015

Manipulation of the configuration of Ag nanowire (NW) networks has been pursued to enhance the performance of stretchable transparent electrodes. However, it has remained challenging due to the high Young's modulus and low yield strain of Ag NWs, which lead to their mechanical failure when subjected to structural deformation. We demonstrate that floating a Ag NW network on water and subsequent in-plane compression allows convenient development of a wavy configuration in the Ag NW network, which can release the applied strain. A greatly enhanced electromechanical stability of Ag NW networks can be achieved due to their wavy configuration, while the NW networks maintain the desirable optical and electrical properties. Moreover, the produced NW networks can be transferred to a variety of substrates, offering flexibility for device fabrication. The Ag NW networks with wavy configurations are used as compliant electrodes for dielectric elastomer actuators. The study demonstrates their promising potential to provide improved performance for soft electronic devices. © The Royal Society of Chemistry.

Yoon S.,Chung - Ang University | Cho J.,Chung - Ang University | Lee H.-K.,Pohang Accelerator Laboratory | Park S.,Korea Institute of Science and TechnologySeoul | And 2 more authors.
Applied Physics Letters | Year: 2015

The effects of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doping on diketopyrrolo-pyrrole-based polymeric semiconductors in terms of charge transport behavior and structural ordering are systematically investigated. Although the energy level offset between the polymeric semiconductor and the F4TCNQ acceptor was not particularly large, ultraviolet photoelectron spectroscopy analyses revealed that a low doping ratio of 1 wt. % is sufficient to tune the energy distance between the Fermi level and the HOMO level, reaching saturation at roughly 5 wt. %, which is further confirmed by the depletion mode measurements of field effect transistors (FETs). Structural analyses using grazing-incidence X-ray diffraction (GIXD) show that the overall degree of edge-on orientation is disturbed by the addition of dopants, with significant influence appearing at high doping ratios (>3 wt. %). The calculated charge carrier mobility from accumulation mode measurements of FETs showed a maximum value of 2 cm2/V·s at the optimized doping ratio of 1%, enabled by additional holes in the channel region, which results in a roughly 40% increase relative to the undoped device. Further increases in the doping ratio, however, resulted in worse FET performance, which can be attributed to structural deformation. This result suggests that the electrochemical doping method can be also applied to donor-acceptor copolymers to further enhance their charge transport characteristics, once the optimized doping condition has been established. © 2015 AIP Publishing LLC.

Singh J.P.,Korea Institute of Science and TechnologySeoul | Gautam S.,Panjab University | Srivastava R.C.,Govind Ballabh Pant University of Agriculture & Technology | Asokan K.,Inter University Accelerator Center | And 2 more authors.
Superlattices and Microstructures | Year: 2015

Abstract Present work investigates the crossover from paramagnetism to superparamagnetism as a function of crystallite size in zinc ferrite nanoparticles using near edge X-ray absorption spectroscopy. Synthesized paramagnetic and superparamagnetic nanoparticles exhibit presence of Fe2+ and Fe3+ ions with dominant concentration of Fe3+ ions. Fe L- and O K-edges spectra of paramagnetic nanoparticles consist of more intense spectral features compared to that of superparamagnetic nanoparticles. This reflects enhanced t2g and eg symmetry states of Fe-O hybridized states in paramagnetic nanoparticles induced by increased degree of crystallization. © 2015 Elsevier Ltd.

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