Seung Hee Lee

Kangbuk Samsung Hospital, Sŏul, Seoul, South Korea

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Publications (300)542.54 Total impact

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    ABSTRACT: A nitrogen-doped carbon layer coated thermally exfoliated graphene (NC-TEG) is prepared by in-situ polymerization of p-phenylene diamine (PD) with thermally exfoliated graphene (TEG) and subsequent high temperature pyrolysis (600 °C for 1 h in argon gas environment). Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy confirm the formation of poly-(p-phenylene diamine) layers on the TEG surfaces with a nitrogen doping level of ~6.1%. Physisorption analysis indicates that NC-TEG not only has the enlarged surface area, but also forms hierarchical three dimensional structures with several micro and meso-pores compared to pristine TEG. Due to the synergic effect of nitrogen atoms in the carbon structures and augmented surface area, the capacitance measured from cyclic voltammetry and galvanic charge–discharge increases to 282.5 F g−1 from the 95.1 F g−1 of TEG. Moreover, the PD monomer acts as a reversible faradaic agent. The capacitive performance of the NC-TEG electrode is investigated in different mixed electrolytes. The specific capacitance is significantly increased to 635.6 F g−1 in a mixed electrolyte of 0.025 M PD and 2 M KOH. After 10,000 cycles, the capacitive retention shows remarkable stability as high as 87.4%.
    Carbon 04/2015; 85. · 6.16 Impact Factor
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    ABSTRACT: An array of three-dimensional TiO2 nanohelixes infiltrated with TiO2 nanoparticles as a multifunctional photoanode for dye-sensitized solar cells is presented. The unique geometry and the near-single crystallinity of TiO2 nanohelixes result simultaneously in strong light scattering and enhanced carrier transport, while maintaining a large surface area by the TiO2 nanoparticles.
    Solar Energy Materials and Solar Cells 01/2015; 132:47–55. · 5.03 Impact Factor
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    ABSTRACT: An efficient approach for the preparation of 9-anthracene carboxylic acid (ACA) modified reduced graphene oxide (rGO) was demonstrated in this study. ACA was used as a surface-modifying agent and underwent a reversible redox reaction. The benzene ring of the ACA anion was attached to the rGO surface via π-π interactions, and the carboxylate anions helped to disperse the hybrid materials in water due to hydrogen bonding. Therefore, water-dispersible, ACA-modified rGO (ACA-rGO) improved the wettability and capacitance performance in aqueous electrolyte solutions. The morphology of the ACA-rGO was studied using transmission electron microscopy and atomic force microscopy image analysis. The dispersion characteristics of the exfoliated materials were investigated using UV-vis spectroscopy analysis. The chemical states and natures of the samples were investigated using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). The appearance of a new peak at 288.7 eV in the XPS of ACA-rGO confirmed the successful surface modification of rGO using ACA. Raman spectra were studied to compare the electronic structure and defect concentrations in the ACA-rGO with respect to GO. The low intensity and shifted D- and G-bands indicated non-covalent functionalization of rGO with ACA anions. Electrochemical performances of ACA-rGO, rGO,and GO were evaluated in 1 M aqueous Na2SO4 electrolyte. The capacitance performance was investigated through galvanometric charge-discharge with ACA-rGO, rGO, and GO in an operating voltage of -1 to 1V. The range of specific capacitance in the three-electrode system was 610 to 115 F g-1 at a current density range of 0.8 to 20 A g-1. In addition, the capacitance performance of ACA-rGO was studied in 1 M Na2SO4 electrolyte using two-electrode systems. The cell capacitance, energy density, and power density at a current density of 0.2 A g-1 of the asymmetric assembly with multiwall carbon nanotubes were 77 F g-1, 41.3 Wh kg-1, and 200 W kg-1, respectively
    RSC Advances 12/2014; · 3.71 Impact Factor
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    ABSTRACT: Seamless stitching of graphene domains on polished copper (111) is proved clearly not only at atomic scale by scanning tunnelling microscopy (STM) and transmission electron micoscopy (TEM), but also at the macroscale by optical microscopy after UV-treatment. Using this concept of seamless stitching, we are able to synthesis 6 cm × 3 cm monocrystalline graphene without grain boundaries on polished copper (111) foil, which is only limited by the chamber size. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 12/2014; · 15.41 Impact Factor
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    ABSTRACT: We report a HC(NH2)2PbI3 perovskite solar cell based on TiO2 nanohelices. Well-aligned helical TiO2 arrays with different pitch (p) and radius (r), helix-1 (p/2 = 118 nm, r = 42 nm), helix-2 (p/2 = 353 nm, r = 88 nm) and helix-3 (p/2 = 468 nm, r = 122 nm), were grown on FTO glass by oblique-angle electron beam evaporation. HC(NH2)2PbI3 perovskite was deposited on the TiO2 nanohelices by two-step dipping method. Helix-1 showed higher short-circuit current density (JSC), while helix-3 exhibited slightly higher open-circuit voltage (VOC). HC(NH2)2PbI3 perovskite combined with helix-1 demonstrated average power conversion efficiency of 12.03±0.07% due to higher JSC compared to helix-2 and helix-3. High JSC from helix-1 was attributed to enhanced light scattering efficiency and higher absorbed photon-to-current conversion efficiency. Moreover, helix-1 showed fast electron diffusion despite longest pathway structure, which was attributed to higher charge injection efficiency due to larger contact area between perovskite and TiO2. We propose here that fine tuning of interface between perovskite and electron injecting oxide is one of crucial factors for achieving high performance perovskite solar cell.
    J. Mater. Chem. A. 11/2014;
  • Synthetic Metals 10/2014; 196:33–37. · 2.22 Impact Factor
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    ABSTRACT: We propose a film patterned retarder (FPR) for stereoscopic three-dimensional display with polarization glasses using ink-jet printing method. Conventional FPR process requires coating of photo-alignment and then UV exposure using wire-grid mask, which is very expensive and difficult. The proposed novel fabrication method utilizes a plastic substrate made of polyether sulfone and an alignment layer, poly (4, 4’ - (9, 9 -fluorenyl) diphenylene cyclobutanyltetracarboximide) (9FDA/CBDA) in which the former and the latter aligns reactive mesogen along and perpendicular to the rubbing direction, respectively. The ink-jet printing of 9FDA/CBDA line by line allows fabricating the cost effective FPR which can be widely applied for 3D display applications.
    Optics Express 09/2014; 22(19). · 3.53 Impact Factor
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    ABSTRACT: We demonstrate distinct entanglement of single-walled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) clusters in nematic liquid crystal medium using scanning electron microscopy technique and the entanglement influence on electric field-induced stretching phenomena of the said clusters in the same medium under optical microscopy investigation. The observed stretching threshold field for MWCNT clusters is found to be higher than the SWCNT counterpart caused by the interplay between attractive field-induced dipolar interaction of intercarbon nanotube (CNT) bundles and the distinct degree of entanglement of neighboring CNT bundles. Subsequently observed different tensile elasticity modulus results for different CNT kinds also confirm different CNT bundle entanglement and attractive dipolar interaction between adjacent CNT bundles in CNT clusters are responsible for distinct stretching threshold field behavior.
    Physical Review E 07/2014; 90(1-1):012508. · 2.33 Impact Factor
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    ABSTRACT: Conventional film patterned retarder (FPR) production requires a photo-alignment layer and a UV exposure process through a patterned wire-grid photo-mask, increasing the cost as well as limiting the resolution of FPR. We proposed a novel method for the fabrication of FPR without using the alignment layer and the photo-mask. Reactive mesogen (RM) was coated on a base film, and then the substrate with 2-domain interdigitated electrodes was contacted over the RM layer. The in-plane electric field reoriented the randomly orientated RM molecules to the field direction, generating the slow axes in each domain. Then, the UV light was exposed to the film, fixing the slow axes of the polymerized RM with orthogonal orientation between neighboring domains. Finally, an incident linearly polarized light gave rise to giving oppositely handed circular polarizations of light after passing the film.
    Optics Express 06/2014; 22(12):15315-15319. · 3.53 Impact Factor
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    ABSTRACT: We propose a novel approach to achieve a homogeneous alignment of nematic liquid crystal (LC). Two bare substrates are rubbed in antiparallel direction and a mixture of LC and reactive mesogen (RM) is filled into the cell using capillary injection, and then UV is exposed after confirming the clear homogenous alignment. The cell shows an excellent dark state and stable electro-optic on/off switching in the IPS cell, which proves polymerized RM on surfaces plays role of alignment layer. Proposed fabrication method has several advantages such as simple process and low cost for IPS cell because alignment layer as well as the coating process is not required.
    SID Symposium Digest of Technical Papers. 06/2014; 45(1).
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    ABSTRACT: In this paper, we investigated effects of stabilizing blue phase liquid crystal using only reactive chiral dopant, without any other monomers and photoinitiators. First, photo-inactive chiral dopants with high helical twist power (~166μm−1) synthesized by us are doped into host nematic LC to induce blue phase and then, the photo-reactive chiral dopant is added to stabilize double twist cylinder. After UV irradiation, BP temperature range is clearly extended compared with pure BP mixture and hysteresis in V-T curve is also dramatically decreased.
    SID Symposium Digest of Technical Papers. 06/2014; 45(1).
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    ABSTRACT: In this paper, we propose a color transparent liquid crystal (LC) mode that can control the properties of the color gamut and transparency in a single panel. To achieve high transmittance in the transparent LC mode, a reactive mesogen (RM) with embedded color dichroic dyes was applied instead of a color filter. Basically, the LC mode applied a 3-terminal electrode structure to switch between the transparent LC mode and the conventional color LC mode. Depending on the direction of the applied voltage, we can operate both the color mode and the transparent mode in a single panel, and modulate the transparency and color purity of the cell through appropriate voltage control. In the experiments, we confirmed that the transmittance and the color gamut of the cell were 39.4% and 2% in the transparent LC mode and 14.9% and 34% in the color LC mode, respectively. Modulation of the color gamut and transparency between each LC mode are also demonstrated in the paper.
    Optics Express 05/2014; 22(10):12505-12512. · 3.53 Impact Factor
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    ABSTRACT: The fringe-field switching-liquid crystal display (FFS-LCD) mode recently became a major component of LCDs for high resolution, high-image quality, low power consumption, and touch screen suitability. This review paper discusses how the FFS technology was developed, how it evolved to its present status, and also about the future advances of the FFS mode in terms of performance and technologies.
    Journal of Information Display. 05/2014; 15(2).
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    ABSTRACT: A multi-electrode driving Fresnel liquid crystal lenticular lens (MeD-Fresnel type LC lens) for switchable 2D/3D liquid crystal displays has been studied. The demonstrated lens which has fine-patterned electrodes only on one substrate, minimizing lens error by mis-assembly between top and bottom substrate, and uses a discontinuous non-uniform electric field with local control of surface pretilt angle by polymer stabilization technique, exhibits excellent lens profile compared with conventional lens without local control of pretilt angle.
    Japanese Journal of Applied Physics 05/2014; 53(6):068003. · 1.06 Impact Factor
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    ABSTRACT: Photo-electrodes with tailored three-dimensional nanostructures offer a large enhancement in light harvesting capability for various optoelectronic devices enabled by strong light scattering in the nanostructures as well as improved charge transport. Here we present an array of three-dimensional titanium dioxide (TiO<sub>2</sub>) nanohelixes fabricated by the oblique angle deposition method as a multifunctional photoanode for CdSe quantum dot sensitized solar cells (QDSSCs). The CdSe QDSSC with a TiO<sub>2</sub> nanohelix photoanode shows a 100% higher power conversion efficiency despite less light being absorbed in CdSe QDs when compared with a conventional TiO<sub>2</sub> nanoparticle photoanode. We attribute the higher power conversion efficiency to strong light scattering by the TiO<sub>2</sub> nanohelixes and much enhanced transport and collection of photo-generated carriers enabled by the unique geometry and near-single crystallinity of the TiO<sub>2</sub> nanohelix structure.
    Optics Express 04/2014; 22(S3). · 3.53 Impact Factor
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    ABSTRACT: Polymer network in vertical alignment liquid crystal cell driven by in-plane field (VA-IPS) is formed in three dimensions to achieve fast response time and to keep the liquid crystal alignment even when an external pressure is applied to the cell. The network formed by UV irradiation to vertically aligned liquid crystal cell with reactive mesogen does not disturb a dark state while exhibiting very fast decaying response time less than 2ms in all grey scales and almost zero pooling mura. The proposed device has a strong potential to be applicable to field sequential display owing to super-fast response time and flexible display owing to polymer network in bulk which supports a gap between two substrates.
    Optics Express 04/2014; 22(9). · 3.53 Impact Factor
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    ABSTRACT: A previous study demonstrated that disaccharides, antioxidants, and caspase inhibitors can be used in freezing solutions to reduce the concentration of Me2SO from the current standard of 10% (v/v) to 5% (v/v) or 2.5% and to eliminate fetal bovine serum (FBS) for the cryopreservation of human amniotic fluid-derived stem cells (AFSCs). Hence, this study investigated whether an irreversible inhibitor of caspase enzymes, benzyloxycarbonyl-Val-Ala-DL-Asp-fluoromethylketone (zVAD-fmk), could be used in post-thaw culture media to increase the survival rate of AFSCs. Our results showed that AFSCs cryopreserved in freezing solution containing trehalose, catalase, and 5% (v/v) Me2SO and then supplemented with zVAD-fmk in the post-thaw culture media showed similar post-thawing viability, proliferation, and apoptosis than cells cryopreserved in the control solution (10% (v/v) Me2SO and 20% FBS). The caspase-3 activity in all the cryopreservation solutions tested was similar to that of the control. Caspase-3, caspase-8, caspase-9, and PARP expression was not found in the cryopreserved cells. In addition, no difference was found in the survival rate and apoptosis between short-term (3 weeks) and long-term (1 year) storage of AFSCs cryopreserved in the solutions used in this study. The results of the present study demonstrate that recovery of cryopreserved cells was enhanced by using a caspase inhibitor in the post-thaw culture media.
    Cryobiology 04/2014; · 1.64 Impact Factor
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    ABSTRACT: For liquid crystal (LC) alignment, polyhedral oligomeric silsesquioxanes (POSS) can be considered as one of the promising candidates for the formation of vertical alignment (VA) of LC. However, because of their poor compatibility and weak interaction with LC hosts, the pristine POSS are highly aggregate themselves in the LC media and create the macroscopic particles, resulting in severe light scatterings. To overcome this barrier, we proposed and successfully synthesized the cyanobiphenyl monosubstituted POSS giant molecule (abbreviated as POSS-CBP1), which showed an excellent dispersion in nematic (N) LC media and formed the perfect VA of LC without using conventional polymer-based VA layers. On the basis of the systematic experiments and careful analysis, we realized that the cyanobiphenyl moiety chemically attached to the pristine POSS with an alkyl chain can significantly improve the initial solubility and interaction with LC media but finely tune POSS-CBP1 to gradually diffuse onto the substrate of LC cell for the formation of VA layer without forming the macroscopic aggregations. Therefore, the newly developed POSS-CBP1 VA layer can allow us to significantly cut the manufacturing cost as well as to open the new doors for electro-optical applications.
    The Journal of Physical Chemistry C 03/2014; 118(12):6300–6306. · 4.84 Impact Factor
  • Jin Hwan Ahn, Yong Seuk Lee, Seung Hee Lee
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    ABSTRACT: We established a method for creation of an anatomic femoral tunnel with minimal damage to the remnant bundle in remnant-preserving anterior cruciate ligament (ACL) reconstruction. The goals of this surgical technique were to preserve the remnant bundle as much as possible, especially at the femoral insertion, and to make the tunnel at the anatomic position. The critical points are that the posterior side of the femoral footprint of the ACL is observed through the posterolateral portal using a 70° arthroscope and a femoral tunnel is made by use of an outside-in technique with remnant preservation. This technique allows for easy viewing of the posterior side of the ACL and enables performance of an anatomic ACL reconstruction.
    Arthroscopy techniques. 02/2014; 3(1):e175-9.
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    ABSTRACT: In general, light propagating an inhomogeneous liquid crystal (LC) cell can be modeled as ‘bundle rays’ because the LC cell consists of many birefringence layers. In order to calculate the optical path of the propagating light in the inhomogeneous LC cell, we multidimensionally calculated the wavevector, k , and the Poynting vector, S , of an ordinary and an extraordinary ray at LC grid interfaces, which are isotropic to a uniaxial medium and a uniaxial-to-uniaxial medium, by using the phase matching method. Furthermore, we also investigated the transmission coefficients and transmittance of the ordinary and the extraordinary rays as a function of difference of the optical axes of the facing birefringence medium at the interface to obtain the significant rays in the LC cell. Finally, we could calculate the exact path of the significant rays in the inhomogeneous LC cell, and compared the ray path in an electrically controlled birefringence (ECB) mode and a twisted nematic (TN) LC mode.
    Journal of Modern Optics 01/2014; 61(3). · 1.17 Impact Factor

Publication Stats

1k Citations
542.54 Total Impact Points

Institutions

  • 2014
    • Kangbuk Samsung Hospital
      Sŏul, Seoul, South Korea
    • Kyungpook National University Hospital
      Sŏul, Seoul, South Korea
  • 2002–2014
    • Chonbuk National University
      • • Department of Polymer Nano Science & Technology
      • • Division of Advanced Materials Engineering
      Tsiuentcheou, North Jeolla, South Korea
  • 2013
    • Southern Illinois University Carbondale
      Illinois, United States
    • Pusan National University
      Tsau-liang-hai, Busan, South Korea
  • 2011
    • Ewha Womans University
      Sŏul, Seoul, South Korea
    • Seoul National University Hospital
      • Department of Radiation Oncology
      Sŏul, Seoul, South Korea
    • Chungbuk National University
      • School of Electrical & Computer Engineering
      Tyundyu, North Chungcheong, South Korea
  • 2008–2011
    • University of Texas at Austin
      • School of Nursing
      Texas City, TX, United States
  • 2005–2011
    • Gwangju Institute of Science and Technology
      • Department of Life Sciences
      Gwangju, Gwangju, South Korea
  • 2010
    • Catholic Sangji College
      Antō, North Gyeongsang, South Korea
    • Sungkyunkwan University
      • Department of Physics
      Seoul, Seoul, South Korea
  • 2008–2010
    • University of Central Florida
      • College of Optics & Photonics
      Orlando, FL, United States
    • Dong-A University
      • Department of Electronics Engineering
      Pusan, Busan, South Korea
  • 2009
    • Catholic University of Daegu
      • Department of Ophthalmology
      Hayang, North Gyeongsang, South Korea
    • Inha University Hospital
      Sinhyeon, South Gyeongsang, South Korea
  • 2005–2009
    • Seoul National University
      • • College of Veterinary Medicine
      • • Department of Agricultural Biotechnology
      Sŏul, Seoul, South Korea
  • 2007–2008
    • Korea Photonics Technology Institute
      Sŏul, Seoul, South Korea
  • 2000–2005
    • Hongik University
      • • Department of Chemical Engineering
      • • Department Electronic and Electrical Engineering
      Sŏul, Seoul, South Korea
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 2004
    • CHA University
      • College of Medicine
      Sŏul, Seoul, South Korea
  • 2000–2001
    • Hong-ik university
      United States
  • 1996
    • Kent State University
      • Liquid Crystal Institute
      Kent, OH, United States