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Pohang, South Korea

Han J.-H.,Pohang Accelerator Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

As an electron beam injector of X-ray free-electron lasers (FELs), photoinjectors have been developed for the past few decades. Such an injector starting with a photocathode RF gun provides high brightness beams and therefore it is being adopted as an injector of X-ray FELs. In this paper we show how to improve photoinjector performance in terms of emittance and repetition rates by means of injector components optimization, especially with the gun. Transverse emittance at the end of an injector is reduced by optimizing the gun design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the gun. It is discussed that a repetition rate of 1 kHz at a normal-conducting S-band photoinjector is feasible by adopting a coaxial RF coupler and improving cooling-water channels surrounding the gun. © 2014 Elsevier B.V.

Song H.-K.,Ulsan National Institute of Science and Technology | Lee K.T.,Ulsan National Institute of Science and Technology | Kim M.G.,Pohang Accelerator Laboratory | Nazar L.F.,University of Waterloo | Cho J.,Ulsan National Institute of Science and Technology
Advanced Functional Materials | Year: 2010

Diversified and extended applications of lithium-ion batteries demand the development of more enhanced materials that can be achieved by sophisticated synthetic methods. Combination of novel materials with strategic design of their shape on the nanometer scale enables a breakthrough to overcome problems experienced by present technologies. In this feature article, an overview is given of Mn-based and polyanion-based cathode materials with nanoscale features for lithium-ion batteries as materials to replace conventional bulk cathode materials. Various synthetic methods coupled with nanostructuring as well as the benefits obtained from the nanostructure are described. Strategic design of electrode materials in a nanoscale dimension provides breakthroughs in battery technologies. Enhanced cathodic materials drive advances of lithium rechargeable batteries in terms of capacity, rate capability, and cyclability. Various nanostructures such as nanoparticles, nanotubes, nanorods, nanoplates, and even the secondary structure of the primary nano-units enable promising materials for cathodes. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim M.G.,Pohang Accelerator Laboratory | Sim S.,The Interdisciplinary Center | Cho J.,The Interdisciplinary Center
Advanced Materials | Year: 2010

Core-shell type nanoalloys in which the Cu atoms uniformly reside as a shell around a core of Sn nanoparticles are achieved by reacting Cu(acac) 2 with tin nanoparticles. The core-shell Sn@Cu nanoparticles further demonstrate significantly improved rate capability at higher C rates than Sn@C nanoparticles. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Egorova O.A.,Pohang University of Science and Technology | Seo H.,Pohang University of Science and Technology | Kim Y.,Pohang University of Science and Technology | Moon D.,Pohang Accelerator Laboratory | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2011

Hidden nuggets of gold: Mono- and divinylgold complexes (see scheme), key intermediates in the gold-mediated cyclization reaction of N-(propargyl) benzamides, are characterized by NMR and X-ray diffraction analyses. The monovinylgold intermediates undergo proto-deauration in acetonitrile by the substrate. In aqueous media, they produce oxidized products. The divinylgold species undergo reductive elimination to produce the corresponding dimerized products. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim T.K.,Ulsan National Institute of Science and Technology | Lee J.H.,Ulsan National Institute of Science and Technology | Moon D.,Pohang Accelerator Laboratory | Moon H.R.,Ulsan National Institute of Science and Technology
Inorganic Chemistry | Year: 2013

A luminescent lithium metal-organic framework (MOF) is constructed from the solvothermal reaction of Li+ and a well-designed organic ligand, bis(4-carboxyphenyl)-N-methylamine (H2CPMA). A Li-based MOF can detect an explosive aromatic compound containing nitro groups as an explosophore, by showing a dramatic color change with concurrent luminescence quenching in the solid state. The detection sites are proven directly through single-crystal-to-single-crystal transformations, which show strong interactions between the aromatic rings of the electron-rich CPMA2- molecules and the electron-deficient nitrobenzene. © 2012 American Chemical Society.

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