Daejeon, South Korea
Daejeon, South Korea

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Ok J.M.,Korea Advanced Institute of Science and Technology | Kim Y.H.,Korea Research Institute of Chemical Technology | Jeong H.S.,Materials Randnter | Yoo H.-W.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Soft Matter | Year: 2013

In this study, we introduce a simple multi-directional rubbing method to generate various periodic patterns of toric focal conic domains (TFCDs), a typical smectic (Sm) LC defect by using the commonly used Sm LC materials, 4′-n-octyl-4-cyano-biphenyl (8CB). We have successfully obtained a variety of spatially arranged TFCD arrays such as parallelogrammic, hexagonal and square arrays by changing the rubbing angle (Ω) between two different rubbing directions. Our experimental results demonstrate that frustration and distortion of nematic LC molecules at the intersections act as effective seeds to help positioning of TFCDs. Furthermore, the existence of nematic-Smectic A (SmA) phase transition is quite important in controlling the arrangement of TFCDs as the alignment of the nematic director strongly influences the arrangement of TFCDs formed in the SmA phase. © 2013 The Royal Society of Chemistry.

Wan Z.,Pusan National University | Kwack W.-S.,Materials Randnter | Lee W.-J.,Pusan National University | Jang S.-I.,Pusan National University | And 9 more authors.
Materials Research Bulletin | Year: 2014

Titanium doped zinc oxide (Ti doped ZnO) films were prepared by atomic layer deposition methods at a deposition temperature of 200 °C. The Ti content in Ti doped ZnO films was varied from 5.08 at.% to 15.02 at.%. X-ray diffraction results indicated that the crystallinity of the Ti doped ZnO films had degraded with increasing Ti content. Transmission electron microscopy was used to investigate the microstructural evolution of the Ti doped ZnO films, showing that both the grain size and crystallinity reduced with increasing Ti content. The electrical resistivity of the Ti doped ZnO films showed a minimum value of 1.6 × 10-3 Ω cm with the Ti content of 6.20 at.%. Furthermore, the Ti doped ZnO films exhibited excellent transmittance. © 2014 Elsevier Ltd.

Lee J.H.,Korea Advanced Institute of Science and Technology | Shin W.H.,Korea Advanced Institute of Science and Technology | Ryou M.-H.,Korea Advanced Institute of Science and Technology | Ryou M.-H.,Korea Basic Science Institute | And 4 more authors.
ChemSusChem | Year: 2012

Lithium ion capacitors (LICs) have recently drawn considerable attention because they utilize the advantages of supercapacitors (high power) and lithium ion batteries (high energy). However, the energy densities of conventional LICs, which consist of a pair of graphite and activated carbon electrodes, are limited by the small capacities of the activated carbon cathodes. To overcome this limitation, we have engaged urea-reduced graphene oxide. The amide functional groups generated during the urea reduction facilitate the enolization processes for reversible Li binding, which improves the specific capacity by 37 % compared to those of conventional systems such as activated carbon and hydrazine-reduced graphene oxide. Utilizing the increased Li binding capability, when evaluated based on the mass of the active materials on both sides, the LICs based on urea-reduced graphene oxide deliver a specific energy density of approximately 106 Wh kgtotal -1 and a specific power density of approximately 4200 W kgtotal -1 with perfect capacity retention up to 1000 cycles. These values are far superior to those of previously reported LICs and supercapacitors, which suggests that appropriately treated graphene can be a promising electrode material for LICs. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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