PVK와 TNF 사이에 형성된 전하이동 착물에 관한 연구(Ⅱ) : C. I. E 表色系에 의한 純度에 대하여 Purity by J.I.E color system

신영진,鄭吉煥,高錫梵 全北大學校 基礎科學硏究所 1978 基礎科學 Vol.1 No.1

Thin films of solid state were made from solutions of organic polymers of different molar mixtures of poly-N-vinyl carbazole (P.V.K) and 2,4,7 -trinitro-9 - fluorenone(T.N.F). The donor, P.V.K. and the acceptor, T.N.F. molecules form a charge transfer complex. Meassuring the color purity of the thin films by using the C.I.E color system we found that the color purity of these polymers was increasing as the molar ratio varied from 1:0.2 to 1:0.6, 0.2 and 0.6 being TNF. This means that these organic polymers form a charge transfer complex up to the molar ratio 1:0.6. It was also found that this charge transfer complex can be classified as intermediatly interacting one by electrical property of these polymers.

의료용 임플란트 금속의 종류와 특성에 관한 고찰

조정환,고영호 고신대학교 자연과학연구소 2007 고신대학교 자연과학연구소 논문집 Vol.14 No.-

의료용 임플란트 금속은 최근에 의학 및 의공학, 치의학 분야의 발달로 인하여 그 수요가 급격히 증가되고 있으며, 종류도 다양해지고 있다. 본 연구에서는 그동안 사용되어 온 의료용 임플란트 금속의 종류와 특성에 관하여 기존의 발표된 문헌에 근거하여 살펴보고 내용을 정리하였다. 금속의 종류로서 스데인레스 강과 코발트 합금, 타이타늄과 그 합금에 대하여 중점적으로 고찰하였다. Metals for medical implants has been expanded in use due to development of medical sciences and engineering, and dental applications. This study aims to analyse and summarize the literatures about materials for medical implants. The discussion was focused on stainless steels, cobalt alloy, titanium and its alloy.

Design optimization of quantum cascade laser structures at λ ∼ 11-12 µm

Ko, Yeong Hwan,Yu, Jae Su Wiley (John WileySons) 2010 Physica status solidi. PSS. A, Applications and ma Vol.207 No.9

Design of hemi-urchin shaped ZnO nanostructures for broadband and wide-angle antireflection coatings

Ko, Yeong Hwan,Yu, Jae Su The Optical Society 2011 Optics express Vol.19 No.1

<P>We study theoretically and experimentally the hemi-urchin shaped zinc oxide (ZnO) nanostructures for broadband and wide-angle antireflection coatings. The antireflective characteristics of hemi-urchin shaped ZnO nanostructures, which can be formed by integrating one-dimensional (1D) nanostructures (i.e., nanorods) on the periodic 2D structural architecture, are investigated. The optimization process is performed using a rigorous coupled-wave analysis method in terms of the order of taper of Si subwavelength gratings (SWGs) as a 2D structural architecture, the geometry of Si SWGs, and the height/size of ZnO nanorods. To simply test an experimental feasibility, a hemi-urchin shaped ZnO nanostructure is fabricated by hydrothermally growing ZnO nanorods on the periodic Si SWG structure. The angle-dependent reflectance of the hemi-urchin shaped ZnO nanostructures on the Si SWG is compared with that of the vertically aligned ZnO nanorod arrays on the Si substrate. The optimized hemi-urchin shaped ZnO nanostructure can significantly improve the antireflective property by suppressing the surface reflection over a broad spectrum and a wide range of angles of light incidence, indicating a reasonable agreement with the experimental results.</P>

Wire-shaped ultraviolet photodetectors based on a nanostructured NiO/ZnO coaxial p-n heterojunction via thermal oxidation and hydrothermal growth processes

Ko, Yeong Hwan,Nagaraju, Goli,Yu, Jae Su The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.6

<P>We report the facile fabrication of wire-shaped ultraviolet photodetectors (WUPDs) by employing a nanostructured zinc oxide (ZnO)/nickel oxide (NiO) coaxial p-n heterojunction. The WUPD consists of a ZnO/NiO coaxial Ni wire and a twisted gold (Au) wire where the Ni and Au are used as the anode and cathode, respectively. For the coaxial p-n heterojunction, the NiO nanostructures (NSs) and the ZnO nanorods (NRs) are subsequently formed on the surface of Ni wire via thermal oxidation and hydrothermal growth processes. With an applied bias of -3.5 V, the WUPD exhibits good photoresponsivity of 7.37 A W(-1) and an external quantum efficiency of 28.1% at an incident light wavelength of 325 nm. Under the UV illumination at a wavelength of 365 nm, the dark current and photocurrent are -3.97 10(-7) and -8.47 10(-6) A, respectively. For enhancing the photocurrent, the WUPD is threaded through a silver (Ag) coated glass tube which acts as a waveguide to concentrate the UV light of 365 nm on the WUPD. As a result, the photocurrent is significantly improved up to -1.56 10(-5) A (i.e., 1.84 times) at the reverse bias of -3.5 V.</P>

PDMS-based Triboelectric and Transparent Nanogenerators with ZnO Nanorod Arrays

Ko, Yeong Hwan,Nagaraju, Goli,Lee, Soo Hyun,Yu, Jae Su American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.9

<P>Vertically-grown ZnO nanorod arrays (NRAs) on indium tin oxide (ITO)-coated polyethylene terephthalate (PET), as a top electrode of nanogenerators, were investigated for the antireflective property as well as an efficient contact surface in bare polydimethysiloxane (PDMS)-based triboelectric nanogenerators. Compared to conventional ITO-coated PET (i.e., ITO/PET), the ZnO NRAs considerably suppressed the reflectance from 20 to 9.7% at wavelengths of 300–1100 nm, creating a highly transparent top electrode, as demonstrated by theoretical analysis. Also, the interval time between the peaks of generated output voltage under external pushing forces was significantly decreased from 1.84 to 0.19 s because the reduced contact area of the PDMS by discrete surfaces of the ZnO NRAs on ITO/PET causes a rapid sequence for triboelectric charge generation process including rubbing and separating. Therefore, the use of this top electrode enabled to operate the transparent PDMS-based triboelectric nanogenerator at high frequency of external pushing force. Under different external forces of 0.3–10 kgf, the output voltage and current were also characterized.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-9/am5018072/production/images/medium/am-2014-018072_0005.gif'></P>

Electrochemical synthesis of ZnO branched submicrorods on carbon fibers and their feasibility for environmental applications

Ko, Yeong Hwan,Ramana, Dandu Kamakshigari Venkata,Yu, Jae Su Springer 2013 Nanoscale research letters Vol.8 No.1

<P>We investigated the structural and optical properties of the hierarchically integrated zinc oxide (ZnO) branched submicrorods on carbon fibers (ZOCF) by scanning/transmission electron microscopy, X-ray diffraction, and photoluminescence (PL) measurements. The ZnO submicrorods were facilely synthesized by an electrochemical deposition method on polyacrylonitrile-based carbon fiber sheets used as a substrate. After coating the ZnO seed layer on the surface of the carbon fibers, ZnO submicrorods were densely grown on the nuclei sites of the seed layer. The prepared ZOCF samples exhibited high crystallinity and good PL properties. A feasibility for environmental application in Pb(II) removal from aqueous solutions was also studied. The ZOCF adsorbent exhibited an excellent maximum adsorption capacity of 245.07 mg g<SUP>−1</SUP>, which could be practically used in Pb(II) removal from water. These fabricated ZOCFs are potentially useful for multifunctional and environmental devices.</P>

Controllable synthesis of periodic flower-like ZnO nanostructures on Si subwavelength grating structures

Ko, Yeong Hwan,Leem, Jung Woo,Yu, Jae Su IOP Pub 2011 Nanotechnology Vol.22 No.20

<P>We report on the periodic well-defined flower-like zinc oxide (ZnO) nanostructures (NSs) self-assembled through a simple hydrothermal method using silicon (Si) subwavelength grating (SWG) structures. The Si SWGs serve as building blocks for constructing a two-dimensional (2D) periodic architecture to integrate the one-dimensional (1D) ZnO NSs. Various controlled morphologies of ZnO NSs with high crystallinity are obtained by changing the growth conditions. For 1D ZnO NSs integrated on periodic hexagonal Si SWG structures, the reflection characteristics are investigated in comparison with the conventional ZnO nanorod (NR) arrays. For a three-dimensional (3D) flower-like ZnO NS on Si SWGs, a relatively low total reflectance of < 8% at wavelengths of 300–1050 nm is achieved compared to the ZnO NRs on Si substrate. </P>

Fabrication and Optimization of Vertically Aligned ZnO Nanorod Array-Based UV Photodetectors via Selective Hydrothermal Synthesis

Ko, Yeong Hwan,Nagaraju, Goli,Yu, Jae Su Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1

<P>Vertically aligned ZnO nanorod array (NRA)-based ultraviolet (UV) photodetectors (PDs) were successfully fabricated and optimized via a facile hydrothermal process. Using a shadow mask technique, the thin ZnO seed layer was deposited between the patterned Au/Ti electrodes to bridge the electrodes. Thus, both the Au electrodes could be connected by the ZnO seed layer. As the sample was immersed into growth solution and heated at 90 °C, the ZnO NRAs were crystallized and vertically grown on the ZnO seed layer, thus creating a metal-semiconductor-metal PD structure. To investigate the size effect of ZnO NRAs on photocurrent, the PDs were readily prepared with different concentrations of growth solution. For the ZnO NRAs grown at 25 mM of concentration, the PD with 10 μm of channel width (i.e., gap distance between two electrodes) exhibited a high photocurrent of 1.91 × 10<SUP>−4</SUP> A at an applied bias of 10 V under 365 nm of UV light illumination. The PD was optimized by adjusting the channel width. For 15 μm of channel width, a relatively high photocurrent on-off ratio of 37.4 and good current transient characteristics were observed at the same applied bias. These results are expected to be useful for cost-effective and practical UV PD applications.</P>

Luminescence properties of europium ions-doped yttrium silicate (Y2SiO5:Eu3+) nanocrystalline phosphors: effect of Eu3+ ion concentration and thermal annealing.

Ko, Yeong Hwan,Lee, Soo Hyun,Yu, Jae Su American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5

<P>The trivalent europium ions-doped yttrium silicate (Y2SiO5:Eu3+) nanocrystalline phosphors were synthesized via a sol-gel method, followed by post thermal annealing. The effects of thermal annealing temperature and doping concentration on the structural and luminescent properties of Y2SiO5:Eu3+ nanocrystalline phosphors were systematically investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence measurements. The nanocrystalline phosphors with a high crystallinity were obtained at an annealing temperature of 1300 degrees C. The luminescent spectra were affected strongly by the Eu3+ ion concentration and annealing temperature. The Eu3+ ion concentration was optimized at 5 mol%, exhibiting excellent red emission (-612 nm) corresponding to the 5D0 --> 7F2 transition of Eu3+ ions at the excitation wavelengths of 262 and 396 nm. For the optimized Y2SiO5:Eu3+ nanocrystalline phosphors, the lifetimes were also estimated from the decay curves under the ultraviolet excitations.</P>