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Bae H.-S.,Kyungpook National University | Haider A.,Kyungpook National University | Selim K.M.K.,Kyungpook National University | Kang D.-Y.,Kyungpook National University | And 2 more authors.
Journal of Polymer Research | Year: 2013

Highly porous polymethyl methacrylate (PMMA) fibers were fabricated via an electrospinning technique using a binary solvent system (8:2 dichloromethane:dimethylformamide) and controlled humidity. The electrospinning process was carried out in a closed hood under humid conditions (varying the humidity from 15 to 70 %). The effects of the concentration, electrospinning parameters, and humidity on the morphology of the PMMA fibers were assessed by field emission scanning electron microscopy (FE-SEM). The surface area, porosity, and mean interfiber pore size of membranes made from the fibers were measured with the Brunauer-Emmett-Teller (BET) method, and the diameter of the fibers was measured using an image analyzer. Nonporous and porous electrospun PMMA fibers exhibited concentration-dependent variations in their morphologies. No effect of the electrospinning parameters, such as the voltage and flow rate, was observed. The porosity of the PMMA fibers increased when the humidity was changed from 15 to 70 %. The porous PMMA fibers had a large surface area (139.0 m2/g) and a small interfiber pore size (34.8 Å), along with an average fiber diameter of 2 μm. The capacities of the porous and nonporous fibrous membranes to adsorb iodine and phenol were tested. The large surface areas of the membranes led to excellent adsorption capacity of the porous PMMA fiber membrane (iodine: 203 mg/g; phenol: 3.73 mg/g), in contrast to the adsorption capacities of the nonporous PMMA fiber membrane (iodine:117 mg/g; phenol: 1.8 mg/g). A facile, easily accessible approach for fabricating porous fiber membranes is presented in this work, and it is believed that the product may find potential application - as a possible substitute for conventional material - in the removal of organic and inorganic pollutants from water. © 2013 Springer Science+Business Media Dordrecht.

Chung D.Y.,Korea Basic Science Institute | Chung D.Y.,Seoul National University | Park S.-K.,Korea Advanced Institute of Science and Technology | Chung Y.-H.,Korea Institute of Science and Technology | And 11 more authors.
Nanoscale | Year: 2014

Edge-exposed MoS2 nano-assembled structures are designed for high hydrogen evolution reaction activity and long term stability. The number of sulfur edge sites of nano-assembled spheres and sheets is confirmed by Raman spectroscopy and EXAFS analysis. By controlling the MoS2 morphology with the formation of nano-assembled spheres with the assembly of small-size fragments of MoS2, the resulting assembled spheres have high electrocatalytic HER activity and high thermodynamic stability. © 2014 The Royal Society of Chemistry.

Chang I.,Seoul National University | Lee M.H.,University of California at Merced | Lee J.-H.,Seoul National University | Kim Y.-S.,Seoul National University | And 2 more authors.
International Journal of Precision Engineering and Manufacturing | Year: 2013

The paper examines a fabrication method of flexible fuel cells (FCs), and its feasibility through a set of electrical measurements both in the as-prepared and the bended condition. The flexible FC consists of three parts: membrane electrode assembly (MEA), anode and cathode endplates with current collectors. The endplate material for anode and cathode used in this study is Polydimethylsiloxane (PDMS), and metallic films are sputtered on a patterned PDMS to use the resulting structure as current collector. The power density of bended cell with the curvature of ~1.8 m-1 decreased by ~30% compared to the as-prepared (non-bended) cell. © 2013 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.

Lee K.-H.,Gwangju Institute of Science and Technology | Kim S.-M.,Korea Photonics Technology Institute KOPTI | Jeong H.,Gwangju Institute of Science and Technology | Pak Y.,Gwangju Institute of Science and Technology | And 10 more authors.
Advanced Materials | Year: 2013

All-solution-processed transparent thin film transistors (TTFTs) are demonstrated with silver grid source/drain electrodes, which are fabricated by printing and subsequent silver nanoparticles solution coating, which allows continuous processing without using high vacuum systems. The silver grid electrode shows a reasonable transmittance in visible range, moderate electrical conductance and mechanical strength. The TTFTs are employed to drive liquid crystal cells and demonstrate a successful switching operation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim B.,Seoul National University | Fujioka S.,RIKEN | Kwon M.,Seoul National University | Jeon J.,Seoul National University | And 2 more authors.
Plant Cell Reports | Year: 2013

Key message: Arabidopsis gulliver3 - D/dwarf4 - D displays growth-promoting phenotypes due to activation tagging of a key brassinosteroid biosynthetic gene DWARF4. In gul3-D/dwf4-D, the Jasmonate and Salicylate signaling pathways were relatively activated and suppressed, respectively. Energy allocation between growth and defense is elegantly balanced to achieve optimal development in plants. Brassinosteroids (BRs), steroidal hormones essential for plant growth, are regulated by other plant hormones, including auxin and jasmonates (JA); auxin stimulates the expression of a key brassinosteroid (BR) biosynthetic gene, DWARF4 (DWF4), whereas JA represses it. To better understand the interaction mechanisms between growth and defense, we isolated a fast-growing mutant, gulliver3-D (gul3-D), that resulted from the activation tagging of DWF4, and examined the response of this mutant to defense signals, including JA, Pseudomonas syringae pv. tomato (Pst DC3000) infection, and wounding. The degree of root growth inhibition following MeJA treatment was significantly decreased in gul3-1D/dwf4-5D relative to the wild type, suggesting that JA signaling is partially desensitized in gul3-1D. Quantitative RT-PCR analysis of the genes involved in JA and salicylic acid (SA) responses, including MYC2, PDF1.2, CORI3, PR1, and PR2, revealed that JA signaling was preferentially activated in gul3-1D, whereas SA signaling was suppressed. As a result, gul3-1D was more susceptible to a biotrophic pathogen, Pst DC3000. Based on our results, we propose a model in which BR and JA cooperate to balance energy allocation between growth and defense responses. In ambient conditions, BRs promote plant growth; however, when stresses trigger JA signaling, JA compromises BR signaling by downregulating DWF4 expression. © 2013 Springer-Verlag Berlin Heidelberg.

Kim K.,Korea Advanced Institute of Science and Technology | Lee E.,Korea Advanced Institute of Science and Technology | Kim J.,Korea Advanced Institute of Science and Technology | Park S.Y.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Journal of Materials Chemistry C | Year: 2013

Flexible and transparent thin film transistors (FTTFTs) can lead to next generation displays that involve large area, future-oriented flexible and transparent displays. In order to achieve stable FTTFTs, solution processes of organic and inorganic compounds have received significant attention. Above all, transparent oxide semiconductors such as ZnO have been studied to enhance flexibility with high electrical performance by integration with organic dielectrics. However, interfacial traps between inorganic and organic compounds are derived by interface dipole, which induce a considerable flat band shift. Herein, we have developed a self-assembled inorganic layer (SAIL) via the photo-induced transformation of a mono-poly(dimethylsiloxane) (PDMS) layer as interface engineering. Especially, the shifting of flat band voltage (V FB) was effectively suppressed by the SAIL process, which was analyzed with a single-piece analytical model for ZnO TFTs. In addition, flexible ZnO/SAIL/polymer dielectric TFTs with low process temperature as high as 200 °C exhibited a good field-effect mobility μ = 0.28 cm2 V-1 s-1, more than 106 on-off current ratio and excellent device operational stability and flexibility. © 2013 The Royal Society of Chemistry.

Chung Y.,Seoul National University | Choe S.,Seoul National University | Choe S.,Advanced Institute of Convergence Technology
Critical Reviews in Plant Sciences | Year: 2013

Brassinosteroids (BRs) are steroid hormones that affect virtually every physiological process of plants throughout their life cycle. In contrast to the rapid progress in our understanding of BR signaling pathways, little is known about the regulatory mechanisms underlying BR homeostasis, particularly the upstream signals that regulate BR biosynthesis and inactivation. BR biosynthesis occurs through network pathways and basically is regulated at the transcriptional level of BR biosynthetic genes. When the BR signal is activated, BR-specific transcription factor, BZR1, inhibits transcription of BR biosynthetic genes through feedback downregulation mechanisms. Moreover, BR biosynthesis is also affected by other hormones such as auxin. This review focuses on recent progress in our understanding of the regulation of BR biosynthesis, with an emphasis on the transcriptional mechanisms that regulate this process, the effect of other hormones, exogenous signals, and inactivation of BRs. © 2013 Copyright Taylor and Francis Group, LLC.

Kwon S.-H.,Korea Advanced Institute of Science and Technology | Kwon S.-H.,Korea Electronics Technology Institute | Park J.,Korea Advanced Institute of Science and Technology | Kim W.K.,Korea Electronics Technology Institute | And 7 more authors.
Energy and Environmental Science | Year: 2014

We demonstrated a new water motion active transducer (WMAT) without any external bias-voltage sources or additional processes, which critically limit the use of conventional passive capacitive transducers that convert mechanical motion into electric energy. From a simple structure, we successfully turned on an LED using various kinds of natural water motion. The WMAT, which has wide applicability, has good potential to be a candidate for generating sustainable electric energy. © The Royal Society of Chemistry 2014.

Lee E.,Korea Advanced Institute of Science and Technology | Ko J.,Korea Advanced Institute of Science and Technology | Lim K.-H.,Korea Advanced Institute of Science and Technology | Kim K.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Advanced Functional Materials | Year: 2014

Solution-processed oxide semiconductors (OSs) used as channel layer have been presented as a solution to the demand for flexible, cheap, and transparent thin-film transistors (TFTs). In order to produce high-performance and long-sustainable portable devices with the solution-processed OS TFTs, the low-operational voltage driving current is a key issue. Experimentally, increasing the gate-insulator capacitances by high-k dielectrics in the OS TFTs has significantly improved the field-effect mobility of the OS TFTs. But, methodical examinations of how the field-effect mobility depends on gate capacitance have not been presented yet. Here, a systematic analysis of the field-effect mobility on the gate capacitances in the solution-processed OS TFTs is presented, where the multiple-trapping-and-release and hopping percolation mechanism are used to describe the electrical conductivity of the nanocrystalline and amorphous OSs, respectively. An intuitive single-piece expression showing how the field-effect mobility depends on gate capacitance is developed based on the aforementioned mechanisms. The field-effect mobility, depending on the gate capacitances, of the fabricated ZnO and ZnSnO TFTs clearly follows the theoretical prediction. In addition, the way in which the gate insulator properties (e.g., gate capacitance or dielectric constant) affect the field-effect mobility maximum in the nanocrystalline ZnO and amorphous ZnSnO TFTs are investigated. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ko J.,Korea Advanced Institute of Science and Technology | Kim J.,Korea Advanced Institute of Science and Technology | Park S.Y.,Korea Advanced Institute of Science and Technology | Lee E.,Korea Advanced Institute of Science and Technology | And 4 more authors.
Journal of Materials Chemistry C | Year: 2014

Solution-processed high-K dielectrics for oxide thin-film transistors (TFTs) have been widely studied with the objective of achieving high performance and low-cost TFTs for next-generation displays. In this study, we introduce an amorphous hafnium-lanthanum oxide (HfLaOx) gate insulator with high electrical permittivity which was fabricated by the simple spin-coating method. In particular, the solution-processed HfLaOx dielectric layer, which was achieved by a mixture of two Hf and La metal hydroxide precursors, showed amorphous properties, a low leakage current and a high dielectric constant. The solution-processed HfLaOx dielectric layers showed a breakdown voltage as high as 5 MV cm-1 in strength and a dielectric constant above 22. Based on their implementation as a gate insulator, the solution-processed ZnO/HfLaOx TFTs showed good and stable performances during operation at a low voltage. A mobility of μ = 1.6 cm 2 V-1 s-1, an on/off current ratio of 10 6, and a threshold voltage of 0.0015 V were obtained under a 5 V gate bias. Our results show the possibility of the solution-processed amorphous HfLaOx dielectric layer as a gate insulator for oxide TFTs. We believe that this amorphous HfLaOx dielectric has good potential for next-generation high-performance TFT devices. © 2013 The Royal Society of Chemistry.

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