Ki Won Kim

Catholic University of Korea, Sŏul, Seoul, South Korea

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Publications (23)31.18 Total impact

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    ABSTRACT: We propose polarization-independent and dual-broadband metamaterial absorbers at microwave frequencies. This is a periodic meta-atom array consisting of metal-dielectric-multilayer truncated cones. We demonstrate not only one broadband absorption from the fundamental magnetic resonances but additional broadband absorption in high-frequency range using the third-harmonic resonance, by both simulation and experiment. In simulation, the absorption was over 90% in 3.93–6.05 GHz, and 11.64–14.55 GHz. The corresponding experimental absorption bands over 90% were 3.88–6.08 GHz, 9.95–10.46 GHz and 11.86–13.84 GHz, respectively. The origin of absorption bands was elucidated. Furthermore, it is independent of polarization angle owing to the multilayered circular structures. The design is scalable to smaller size for the infrared and the visible ranges.
    Optics Express 02/2015; 23(4). DOI:10.1364/OE.23.003861 · 3.49 Impact Factor
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    ABSTRACT: A small-size metamaterial perfect absorber operating at low frequency is proposed. Due to the special design, the unit-cell dimension with respect to wavelength is very small, a/λ ~ 1/17, at the absorption frequency of 377 MHz. The absorption frequency is strongly dependent on the length of zigzag wire. In addition, the absorption is more than 94% in a wide range of incident angle of electromagnetic wave up to 50°. The results show that the proposed absorber is promising to be applied into devices in radio region.
    11/2014; 5(4):045008. DOI:10.1088/2043-6262/5/4/045008
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    ABSTRACT: We propose a dual-band metamaterial perfect absorber at microwave frequencies. Using a planar metamaterial, which consists of periodic metallic donut-shape meta-atoms at the front separated from the metallic plane at the back by a dielectric layer, we demonstrate the multi-plasmonic high-frequency perfect absorptions induced by the third-harmonic as well as the fundamental magnetic resonances. The origin of the induced multi-plasmonic perfect absorption was elucidated. It was also found that the perfect absorptions at dual peaks are persistent with varying polarization.
    Optics Express 12/2013; 21(26):32484-90. DOI:10.1364/OE.21.032484 · 3.49 Impact Factor
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    ABSTRACT: The classical electromagnetically-induced transparency (EIT)-like switching in metamaterials was experimentally demonstrated in the microwave-frequency region. The metameterial unit cell consists of two identical split-ring resonators, which are arranged on both sides of a dielectric substrate with 90°-rotation asymmetry. In our scheme, the classical EIT-like switching can be achieved by changing the polarization of the incident electromagnetic wave.
    Journal of Nonlinear Optical Physics & Materials 05/2013; 22(01). DOI:10.1142/S0218863513500045 · 0.48 Impact Factor
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    ABSTRACT: We propose multi-band metamaterial absorbers at microwave frequencies. The design, the analysis, the fabrication, and the measurement of the absorbers working in multiple bands are presented. The numerical simulations and the experiments in the microwave anechoic chamber were performed. The metamaterial absorbers consist of an delicate arrangement of donut-shape resonators with different sizes and a metallic background plane, separated by a dielectric. The near-perfect absorptions of dual, triple and quad peaks are persistent with polarization independence, and the effect of angle of incidence for both TE and TM modes was also elucidated. It was also found that the multiple-reflection theory was not suitable for explaining the absorption mechanism of our investigated structures. The results of this study are promising for the practical applications.
    Optics Express 04/2013; 21(8):9691-702. DOI:10.1364/OE.21.009691 · 3.49 Impact Factor
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    ABSTRACT: LiCoO2 thin films were fabricated by direct current magnetron sputtering method on STS304 and Ti substrates. The effects of substrate and annealing on their structural and electrochemical properties of LiCoO2 thin film cathode were studied. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction and field emission scanning electron microscopy. The as-deposited films on both substrates have amorphous structure. The (104) oriented perfect crystallization was obtained by annealing over 600 degrees C in STS304 substrate. The LiCoO2 thin film deposited on Ti substrate shows the (003) texture after annealing at 700 degrees C. The electrochemical properties were investigated by the cyclic voltammetry and charge-discharge measurement. The 600 degrees C-annealed LiCoO2 film deposited on STS304 substrate exhibits the inithial discharge capacity of 22 uAh/cm2 and the 96% capacity retention rate at 50th cycles. The electrochemical measurement on annealed films over 600 degrees C was impossible due to the formed TiO2 insulator layer using Ti substrate. As a result, it was found that the STS304 substrate seems to be more suitable material than the Ti substrate in fabricating LiCoO2 thin film cathode.
    Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5937-41. DOI:10.1166/jnn.2012.6399 · 1.34 Impact Factor
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    ABSTRACT: We experimentally demonstrated a controllable electromagnetically induced transparency (EIT)-like spectral response at microwave frequencies in a planar metamaterial consisting of two identical split-ring resonators (SRRs) with side-by-side symmetry. In our scheme, phase coupling between the two SRRs (serving as the bright mode), which were excited strongly by the incident wave, was employed, and it was found that the EIT-like spectral response could be controlled by simply adjusting the incident angle. Thus, our scheme may be used for electromagnetic-wave switching. A high group index for slow-light application and a high quality factor could be obtained by simply controlling the incident angle.
    Journal of Applied Physics 04/2012; 111(7). DOI:10.1063/1.3699197 · 2.19 Impact Factor
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    ABSTRACT: Using a planar metamaterial, which consists of two silver strips, we theoretically demonstrate the plasmonic electromagnetically-induced transparency (EIT)-like spectral response at optical frequencies. The two silver strips serve as the bright modes, and are excited strongly by the incident wave. Based on the weak hybridization between the two bright modes, a highly-dispersive plasmonic EIT-like spectral response appears in our scheme. Moreover, the group index is higher than that of another scheme which utilizes the strong coupling between the bright and dark modes.
    Optics Express 10/2011; 19(22):21652-7. DOI:10.1364/OE.19.021652 · 3.49 Impact Factor
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    ABSTRACT: We propose that the plasmonic electromagnetically-induced transparency (EIT) is accessible based on the second-order magnetic plasmon resonance (MPR) in the stacked optical metamaterial with a symmetric structure. In order to clarify the role of high-order MPR, we systematically analyze the propagation and the distribution of electromagnetic waves of the plasmonic EIT in both the symmetric and the asymmetric structures. This not only sharpens our understanding of the existing concept, but also provides a profound insight into the plasmonic coherent interference in the near-field zone.
    Optics Communications 08/2011; 284(4):4766-4768. DOI:10.1016/j.optcom.2011.05.052 · 1.54 Impact Factor
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    ABSTRACT: Carbon nanotubes (CNTs) were purified using acid solution, and CNT-sulfur composite powder was prepared via precipitation, using the purified CNTs. In addition, the effect of the purified CNTs (PUCNTs) on the electrochemical performance of the Li/S cell was investigated. After the purification, almost all the impurities in the as-synthesized CNTs (ASCNTs) were removed, and the dispersibility of the CNTs was improved. On the other hand, the concentration of the structural defects and of the disordered structures in the PUCNTs was increased due to the surface oxidation of the tubes during acid treatment. In the case of the PUCNT-S composite powder, the outer wall of the tubes was well covered with sulfur, as opposed to the tubes in the ASCNT-S composite powder. The Li/S cell containing ASCNT-S composite cathode showed a large voltage decrease and a 680 mAh/g capacity during the first discharge process. The Li/S cell with PUCNT-S composite cathode, however, showed a higher discharge capacity and better cycle performance than the cell with ASCNT-S composite cathode. The electrochemical performance of the Li/S cell was improved for the PUCNT-S composite cathode using the CNTs purified by acid treatment.
    Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5800-5. DOI:10.1166/jnn.2011.4331 · 1.34 Impact Factor
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    ABSTRACT: Total knee arthroplasty (TKA) using a cemented technique has been recommended in patients with rheumatoid arthritis owing to the initial stability of the fixation and long-term durability of the components; however, similar long-term follow-up results have been reported in patients who have undergone cementless TKA. The purpose of this study was to evaluate the radiologic and clinical outcomes of cementless TKA in patients with rheumatoid arthritis. We enrolled patients undergoing cementless TKA from March 1990 to February 2000. Clinical and radiologic evaluations were performed using the Knee Society clinical rating system and radiographic evaluation and scoring system. We included the cases of 112 patients who underwent 179 cementless TKA procedures in our analysis. Their mean age was 62.3 years, and the mean follow-up period was 10.1 years. The final survival rate was 0.968 at the 15.5-year follow-up. Regarding radiologic results after surgery, the mean total valgus angle was 6.7°, the mean femoral flexion angle was 97.5° and the mean tibial angle was 89.2° on the anteroposterior radiographs. On the lateral films, the mean femoral flexion angle was 1.6° and the mean tibial angle was 89.2°. At the last follow-up, the mean total valgus angle was 6.5°, the mean femoral flexion angle was 97.4° and the mean tibial angle was 89.1°, as seen on the anteroposterior view. On the lateral views, the mean femoral flexion angle was 1.4° and the mean tibial angle was 89.0°. Regarding the clinical outcome, the mean knee score and function score on the Knee Society clinical rating system were also enhanced from 47.5 and 43.6, respectively, before the operation to 91.2 and 82.3, respectively, at the last follow-up. On radiologic and clinical follow-up of cementless TKA for patients with rheumatoid arthritis, there were no serious complications, and the results of the operation were satisfactory with improvement in range of motion and clinical symptoms.
    Canadian journal of surgery. Journal canadien de chirurgie 06/2011; 54(3):179-84. DOI:10.1503/cjs.000910 · 1.27 Impact Factor
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    ABSTRACT: Various kinds of β-Ga2O3 nanomaterials such as nanowires, nanorods, nanobelts, nanosheets and nanocolumns have been successfully synthesized by simple evaporation of gallium powder with no assisted catalyst in a flow of argon gas. The as-synthesized materials were pure, structurally uniform, single crystalline with monoclinic β-Ga2O3 structure (space group: C2 m−1) and free from defects. The synthesized nanomaterials were deposited with a growth order of nanocolumn/nanorod, nanowire/nanobelt and nanosheet with synthesis time. The nucleation site was looked over in detail. We present evidence that the surface, edge and tip of previously grown β-Ga2O3 nanomaterials again provide a nucleation site of new β-Ga2O3 nanomaterials. Because no metal catalysts were introduced into our growth, a vapor–liquid–solid (VLS) growth is not the likely process in this work, indicating that the observed nanomaterials were grown via a vapor–solid (VS) mechanism.
    Physica Scripta 05/2010; 2010(T139):014079. DOI:10.1088/0031-8949/2010/T139/014079 · 1.30 Impact Factor
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    ABSTRACT: Fe2O3 thin films are important for the fabrication of rechargeable lithium microbatteries. Thin films of Fe2O3 were prepared by the electrostatic spray deposition (ESD) technique by using iron chloride as the precursor. The thin film electrodes, without inert additives such as polymer binder and conducting material, can deliver a first discharge capacity of 912 mA h g−1 and retain a discharge capacity of 537 mA h g−1 at a current density of 200 mA g−1 to the 100th cycle. The coulombic efficiency of the Fe2O3 thin-film electrode was over 96% after several cycles.
    Physica Scripta 05/2010; DOI:10.1088/0031-8949/2010/T139/014066 · 1.30 Impact Factor
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    ABSTRACT: Polycrystalline Cu-doped ZnO films have been successfully fabricated, and room-temperature ferromagnetism (RTFM) has been achieved. Sputtering of a Cu-chip-embedded ZnO target enabled a low-doping concentration of Cu. RTFM was obtained for the entire substrate temperature range from RT to 300 • C. However, the best result was obtained at a substrate temperature of 100 • C, and the magnetic properties of the Cu-doped ZnO films turned out to be very sensitive to the crystalline structure.
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    ABSTRACT: β-Ga2O3 nanowires with different diameters were successfully synthesized by adjusting the size of catalyst via a simple thermal evaporation of elemental gallium powder in argon ambient. The size of catalyst was controlled by adjusting the sputtering time. The critical size of catalyst, which can be provided as a seed of nanowires, was investigated in detail. In this work, we have found that the growth mechanism of nanowires can be changed on the basis of catalyst size. The Ga2O3 nanowires synthesized by the vapor–liquid–solid (VLS) mechanism were successfully grown on the catalyst with a diameter not exceeding 65nm. The HRTEM results indicate that the growth direction of nanowires synthesized by the VLS mechanism strongly depends upon the crystal direction of the catalyst.
    Journal of Crystal Growth 02/2009; 311(4):1195-1200. DOI:10.1016/j.jcrysgro.2008.11.054 · 1.69 Impact Factor
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    ABSTRACT: Carbon nanotubes (CNTs) have been synthesized through chemical vapor deposition in argon gas atmosphere using Fe–2.5%Mo alloyed nanoparticles as a catalyst and H2/CH4 gas mixture as a reaction gas. Fe–2.5 wt.%Mo alloyed nanoparticles with average diameter of 7, 20, 45 and 85 nm are prepared by the chemical vapor condensation process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and molybdenum hexacarbonyl (Mo(CO)6). The morphologies of the CNTs are controlled by adjusting the nanoparticle size, reaction gas ratio and reaction temperature. With decreasing nanoparticle size under the same experimental conditions, the degree of crystalline perfection increases gradually and the morphologies of the carbon nanotubes vary from multi wall carbon nanotubes to single wall carbon nanotubes. Also, the ratio of reaction gas has an effect on the morphology and the degree of crystallinity of CNTs. In this work, it is suggested that morphology, diameter and degree of crystallinity of CNTs could be controlled by adjusting the reaction gas ratio, reaction temperature and catalyst size.
    Physica Scripta 11/2007; 2007(T129):17. DOI:10.1088/0031-8949/2007/T129/004 · 1.30 Impact Factor
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    ABSTRACT: Polymer electrolyte (PE) based on poly(ethylene oxide)-lithium bis(trifluoromethane sulfonyl)imide (PEO-LiTFSI) was blended with three room temperature ionic liquids (RTILs), namely 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (BMITFSI), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMICF3SO3) with a view to enhance the room temperature ionic conductivity to acceptable levels for use in lithium batteries. The incorporation of 80 parts by weight (pbw) of the RTILs in 100 pbw of PEO-LiTFSI resulted in enhanced ionic conductivity, the effect being more pronounced at lower temperatures. Evaluation of electrochemical properties showed that PEs with RTILs exhibit an electrochemical stability window between −1.0 V and 4.5 V vs Li/Li+ and good reversibility of redox reactions on cycling. The optimum results were obtained with the incorporation of BMITFSI in the PE, which exhibited a low and stable interfacial resistance on lithium metal.
    Macromolecular Symposia 04/2007; 249-250(1):183 - 189. DOI:10.1002/masy.200750330
  • Solid State Phenomena 01/2007; 124-126:1493-1496. DOI:10.4028/www.scientific.net/SSP.124-126.1493
  • Solid State Phenomena 01/2007; 124-126:1007-1010. DOI:10.4028/www.scientific.net/SSP.124-126.1007
  • Solid State Phenomena 01/2007; 124-126:971-974. DOI:10.4028/www.scientific.net/SSP.124-126.971