Seung Hee Lee

Pohang University of Science and Technology, Geijitsu, Gyeongsangbuk-do, South Korea

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Publications (365)695.52 Total impact

  • Journal of Physics D Applied Physics 11/2015; 48(46):465506. DOI:10.1088/0022-3727/48/46/465506 · 2.72 Impact Factor
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    Hyunah Kwon · Seung Hee Lee · Jong Kyu Kim ·
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    ABSTRACT: Three-dimensional (3D) nanostructured thin films have attracted great attention due to their novel physical, optical, and chemical properties, providing tremendous possibilities for future multifunctional systems and for exploring new physical phenomena. Among various techniques to fabricate 3D nanostructures, oblique angle deposition (OAD) is a very promising method for producing arrays of a variety of 3D nanostructures with excellent controllability, reproducibility, low cost, and compatibility with modern micro-electronic processes. This article presents a comprehensive overview of the principle of OAD, and unique structural and optical properties of OAD-fabricated thin films including excellent crystallinity, accurate tunability of refractive indices, and strong light scattering effect which can be utilized to remarkably enhance performances of various systems such as antireflection coatings, optical filters, photoelectrodes for solar-energy-harvesting cells, and sensing layers for various sensors.
    Nanoscale Research Letters 09/2015; 10(1):369. DOI:10.1186/s11671-015-1057-2 · 2.78 Impact Factor
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    ABSTRACT: Multiwalled carbon nanotubes (MWCNTs) exhibited distinct electrical stretching behavior in nematic liquid crystals (NLC) depending on nanotube surface state. We found that two different samples prepared by chemical functionalization (f-CNT) and physical grinding (g-CNT) revealed distinct field dependence from each other. The threshold stretching field was lower in the f-CNT aggregates than in g-CNT aggregates. This was attributed to polar functionality induced weakened van der Waals interaction in f-CNTs, which was confirmed in infrared (IR) and Raman spectroscopy. Dynamic reorientation of f-CNTs was observed under polarized optical microscopy where f-CNTs were found to follow orientation of NLC director. Uniformly aligned f-CNTs also exhibited selective light absorption in sufficiently long transient field off-state which could find potential applications in memory and modulator devices as well as the versatile functional composites.
  • Source
    Namhee Kim · Seung Hee Lee · Jongyoun Yi · Chulhun L Chang ·
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    ABSTRACT: Peptide nucleic acid (PNA) probes are artificial DNA analogues with a hydrophobic nature that can penetrate the mycobacterial cell wall. We evaluated a FISH method for simultaneous detection and identification of Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacteria (NTM) in clinical respiratory specimens using differentially labeled PNA probes. PNA probes targeting the mycobacterial 16S ribosomal RNA were synthesized. The cross-reactivity of MTB- and NTM-specific probes was examined with reference strains and 10 other frequently isolated bacterial species. A total of 140 sputum specimens were analyzed, comprising 100 MTB-positive specimens, 21 NTM-positive specimens, and 19 MTB/NTM-negative specimens; all of them were previously confirmed by PCR and culture. The PNA FISH test results were graded by using the United States Centers for Disease Control and Prevention-recommended scale and compared with the results from the fluorochrome acid-fast bacterial stain. The MTB- and NTM-specific PNA probes showed no cross-reactivity with other tested bacterial species. The test results demonstrated 82.9% agreement with the culture results with diagnostic sensitivity of 80.2% and diagnostic specificity of 100.0% (kappa=0.52, 95% confidence interval: 0.370-0.676). Dual-color PNA FISH showed high specificity for detecting and identifying mycobacteria in clinical specimens. However, because of its relatively low sensitivity, this method could be more applicable to culture confirmation. In application to direct specimens, the possibility of false-negative results needs to be considered.
    Annals of Laboratory Medicine 09/2015; 35(5):500-5. DOI:10.3343/alm.2015.35.5.500 · 1.48 Impact Factor
  • Seung Hee Lee · Jong Won Park · Koo Young Yoon ·

    08/2015; 18(3):207-215. DOI:10.7846/JKOSMEE.2015.18.3.207
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    Chunfei Zhang · Tapas Kuila · Nam Hoon Kim · Seung Hee Lee · Joong Hee Lee ·
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    ABSTRACT: High quality flower-like NiCo2O4 has been fabricated on three-dimensional (3D) graphene foam (GF) and used as an electrode for supercapacitors. The 3D GFs are prepared through chemical vapor deposition (CVD) followed by the electro-deposition of flower-like NiCo2O4. The NiCo2O4/3D GF nanohybrids are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. The lack of defects in the 3D GF ensures the formation high quality graphene sheets by CVD method. The supercapacitor performances of the electrode materials are evaluated through cyclic voltammetry, charge-discharge analysis and electrochemical impedance spectroscopy. A maximum specific capacitance of 1402 F g−1 is achieved at a current density of 1 A g−1. The NiCo2O4/3D GF nanohybrid-based supercapacitors exhibit long-cycle stability with a 76.6% retention in specific capacitance after 5000 cycles at a current density of 5 A g−1. The high electrochemical performance is attributed to the synergistic effects of the high electrical conductivity and large surface area of 3D GF along with the catalytic activity of the flower-like NiCo2O4.
    Carbon 08/2015; 89:328-339. DOI:10.1016/j.carbon.2015.03.051 · 6.20 Impact Factor
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    ABSTRACT: Electrically tunable focusing microlens arrays based on polarization independent optical phase of nano liquid crystal droplets dispersed in polymer matrix are demonstrated. Such an optical medium is optically isotropic which is so-called an optically isotropic liquid crystals (OILC). We not only discuss the optical theory of OILC, but also demonstrate polarization independent optical phase modulation based on the OILC. The experimental results and analytical discussion show that the optical phase of OILC microlens arrays results from mainly orientational birefringence which is much larger than the electric-field-induced birefringence (or Kerr effect). The response time of OILC microlens arrays is fast~5.3ms and the tunable focal length ranges from 3.4 mm to 3.8 mm. The potential applications are light field imaging systems, 3D integrating imaging systems and devices for augment reality.
    Optics Express 06/2015; 23(13):17337-17344. DOI:10.1364/OE.23.017337 · 3.49 Impact Factor
  • Dhruv Pratap Singh · Seung Hee Lee · Il Yong Choi · Jong Kyu Kim ·
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    ABSTRACT: A simple single-step method to fabricate spatially graded TiO<sub>2</sub>-SiO<sub>2</sub> Bragg stack with rainbow colored photonic band gap is presented. The gradation in thickness of the Bragg stack was accomplished with a modified glancing angle deposition (GLAD) technique with dynamic shadow enabled by a block attached to one edge of the rotating substrate. A linear gradation in thickness over a distance of about 17 mm resulted in a brilliant colorful rainbow pattern. Interestingly, the photonic band gap position can be changed across the whole visible wavelength range by linearly translating the graded Bragg stack over a large area substrate. The spatially graded Bragg stack may find potential applications in the tunable optical devices, such as optical filters, reflection gratings, and lasers.
    Optics Express 06/2015; 23(13):17568-17575. DOI:10.1364/OE.23.017568 · 3.49 Impact Factor
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    ABSTRACT: Uniformly oriented macroscopic monodomain of cholesteric blue phase liquid crystal has been realised by the influence of surface anchoring. Orientation of the lattice planes in surface-treated (ST) and non-surface-treated (NST) cell were analysed and compared by Kossel diagram technique. NST cell has revealed the green and blue domains corresponding to reflection from oriented (110) and (112) planes of the body-centred cubic lattice. However, in the ST cell only the lattice plane (110) oriented uniformly and tailored the macroscopic monodomain. Electric field driven reorientation of the (110) lattice plane was noticed in NST cell whereas for ST cell such reorientation was absent. Two distinct electric field-induced capacitive responses have been observed in the two different cells. In NST cell anomalous electrostriction was observed, whereas for ST cell normal electrostriction was observed. Interestingly, the capacitance has decreased with an increasing electric field for anomalous electrostriction in NST cell, whereas for normal electrostriction in ST cell it was increased with increasing the field. Such a capacitive change behaviour is explained by dielectric anisotropic change followed by the electric field induced elongation and contraction of the cubic unit cell along and perpendicular to the electric field.
    Liquid Crystals 06/2015; 42(8):1-9. DOI:10.1080/02678292.2015.1025874 · 2.49 Impact Factor
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    ABSTRACT: We investigated how the electro-optic characteristics of the fringe-field switching (FFS) liquid crystal (LC) mode are affected by elastic constants of LCs. Unlike conventional liquid crystal (LC) devices, in which mainly the dielectric torque determines reorientation of LC, the field-induced LC reorientation in the fringe-field switching (FFS) mode is controlled first by dielectric torque and then by pure elastic torque between LCs so that the transmittance oscillates along the electrode positions. We find that elastic constants of the LC play an important role on the field-induced dynamics of the LC molecules such that the higher the splay constant is, the higher the light efficiency becomes, which is a unique characteristic of the FFS mode. The results present an important design of physical properties of LC to enhance better transmittance in the FFS mode.
    Liquid Crystals 06/2015; 42(9):1-8. DOI:10.1080/02678292.2015.1033772 · 2.49 Impact Factor
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    ABSTRACT: A reduced graphene oxide (RGO)-NiFe2O4 nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe2O4 nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni3+ and Ni2+, and Fe2+ and Fe3+, respectively. Further, the electrochemical activity of the RGO-NiFe2O4 nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe2O4 modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe2O4 and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe2O4. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe2O4 modified GCE. Therefore, the RGO-NiFe2O4 modified GCE can be used for the electrochemical oxidation of hydrazine.
    Composites Part B Engineering 06/2015; 79:649-659. DOI:10.1016/j.compositesb.2015.05.029 · 2.98 Impact Factor
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    ABSTRACT: We report the H2 and LPG gas sensing behavior of RGO/SnO2 QDs synthesized by surfactant assisted hydrothermal method. The RGO/SnO2 QDs based sensor shows high response ~89.3% to H2 and ~92.4% to LPG for 500 ppm test gas concentration at operating temperatures 200 °C and 250 °C, respectively. Further, the RGO/SnO2 QDs based sensor shows good selectivity to H2 and LPG in the presence of other interfering gases such as ammonia, chloroform, toluene, benzene, acetone, n-butylacetate, acetic acid and formic acid. We observed that the gas response to H2 is 29.8 times higher than that of acetic acid whereas gas response to LPG is 17.8 times higher than that of formic acid. The long-term analyses have also been performed to demonstrate the reproducible nature of RGO/SnO2 QDs based sensor over passing time which shows excellent reproducibility.
    Nanoscale 06/2015; 7(28). DOI:10.1039/C5NR02837J · 7.39 Impact Factor
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    ABSTRACT: The fringe-field switching (FFS) mode that uses liquid crystals (LC) with negative dielectric anisotropy is used in high resolution FFS-LCD owing to its higher transmittance over positive LC. In this paper, the FFS mode with electrode width 1 µm and distances between the electrodes 1.5 µm is proposed. In such an electrode structure, operating voltage (Vop) decreases with decreasing cell gap to 2 µm so that a proper Vop, high LC's light efficiency of 90%, and a fast response time less than 10 ms, can be achieved, which maximizes electro-optic performance of the FFS mode. In addition, the color temperature of a white state becomes higher in the fine patterned FFS cell.
    06/2015; 46(1). DOI:10.1002/sdtp.10100
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    ABSTRACT: Defects in graphene governs electrical and optical properties. Although grain boundaries in graphene inevitably formed during large area synthesis process, which act as scattering centers for charge carriers to degrade mobility, have been studied extensively, point defects have been rarely investigated mainly due to the absence of facile observation tools. Here, we report polarized optical microscopy to observe defect distributions in monolayer graphene. This was realized by aligning liquid crystal s (LC) on graphene where the defect population was modulated by irradiating ultraviolet (UV) light directly on graphene surface under moisture condition. Aromatic rings in LC molecules are oriented with hexagonal rings in graphene to have preferred orientation, providing a way to identify relative orientations of graphene domains and point defects. Our studies show that point defects generated by prolonged UV irradiation time give rise to irregular LC alignment with disclination lines on the graphene surface and a large-size LC domain associated with graphene single domain eventually disappeared. This indicates that defects associated with oxygen-containing functional groups cause to reduce the strong stacking interaction between graphene and LC molecules.
    Optics Express 06/2015; 23(11):14162. DOI:10.1364/OE.23.014162 · 3.49 Impact Factor
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    ABSTRACT: Polymer dispersed nano-sized liquid crystal (LC) composite which is an optically isotropic liquid crystal (OILC) has been investigated looking for its application to flexible liquid crystal displays (LCDs). In the device, nematic LC droplets with its diameter of 242nm are dispersed in polymer matrix so that the LCD has many advantages such as free touch mura, high contrast ratio, rubbing free, wide viewing angle and its phase stability with least hysteresis. However, it needs to overcome high operating voltage and low transmittance. Optimization of LC mixture and controlling ratio of LC and Polymer in the mixture to overcome such barriers are required.
    06/2015; 46(1). DOI:10.1002/sdtp.10038
  • Libo Weng · Seung Hee Lee · Liang‐Chy Chien ·
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    ABSTRACT: A liquid crystal device which shows the capacity to perform as an electrical switchable diffraction grating is demonstrated. Periodical modulation in field-induced refractive index was realized in the in-plane switching liquid crystal device with vertical alignment, which resulted in distinct voltage-dependent diffraction patterns.
    06/2015; 46(1). DOI:10.1002/sdtp.10091
  • Min Su Kim · Hyeun-Seok Choi · Seung Hee Lee · Chanjoong Kim ·
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    ABSTRACT: We study the optical characteristics of a home-built line-laser surface light scattering system that detects sub-micron scale irregularities on a large area in high speeds. The sensitivity of the detection system, i.e. signal to noise (STN) ratio, is found to depend strongly on the detection angle. We find optimal detection angle at 30°, at which (STN) ratio is maximized for 2500 nm silica particles on wafer surface. Experimental results of scattering intensity measurements from a smooth surface and from surfaces with spherical irregularities are in excellent agreement with corresponding theoretical model calculations. The line scan speed can be as high as ∼17 mm/s, while identifying the presence of a particle as small as 700 nm in a pixel area (∼15 μm × ∼17 μm). The presence of irregularities found by the line scan system is confirmed by confocal laser-scanning microscopy imaging. Due to unique advantages such as non-disruptiveness, high-speed over large area, and high sensitivity, this line scan system may be used as a surface inspection system that meets the requirement of recent flat panel display manufacturing environments.
    Current Applied Physics 05/2015; 15(8). DOI:10.1016/j.cap.2015.04.042 · 2.21 Impact Factor
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    Yinan Yan · Tapas Kuila · Nam Hoon Kim · Seung Hee Lee · Joong Hee Lee ·
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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. DOI:10.1016/j.carbon.2014.12.069 · 6.20 Impact Factor
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    ABSTRACT: Adsorption and desorption of ions at interface between liquid crystal and alignment layer in liquid crystal displays play a crucial role in residual direct current voltage associated with image sticking. In this article, the dependency of such adsorption and desorption of ions on resistivity of alignment layer and sign of liquid crystal dielectric anisotropy in the fringe-field liquid crystal cell has been investigated. Our studies show that the time constant of ions during adsorption and desorption depends upon resistivity and dielectric constant of liquid crystal and alignment layer, and most strongly influenced by the resistivity of alignment layer such that the one with lower resistivity in two orders shows much faster adsorption and desorption at the interface than that of the one with higher resistivity.
    Liquid Crystals 04/2015; 42(4):486-491. DOI:10.1080/02678292.2014.1000407 · 2.49 Impact Factor
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    ABSTRACT: Optically isotropic liquid crystal (OILC) mixtures utilising polymerisation-induced phase separation in mixtures of prepolymers and liquid crystals (LCs) have been made and their overall electro-optic performances have been tested by applying an in-plane electric field for flexible display application. Excellent transparent films with a LC to prepolymer weight ratio of 42:58 are achieved and confirmed by SEM images. The average LC droplet size inside the polymer matrix is 215 nm. Consequently, an in-plane driven LC device with a crossed polariser shows a very high contrast ratio over 1000 comparable to the conventional nematic in-plane switching cell, wide viewing angle, a low threshold voltage of 8.2 V, hysteresis free and fast response time. The proposed LC device is free from an alignment layer and the rubbing process and its dark state is not disturbed by mechanical pressure, which can open its application to flexible liquid crystal displays.
    Liquid Crystals 04/2015; 42(4):530-536. DOI:10.1080/02678292.2015.1006698 · 2.49 Impact Factor

Publication Stats

3k Citations
695.52 Total Impact Points


  • 2014-2015
    • Pohang University of Science and Technology
      • Department of Materials Science and Engineering
      Geijitsu, Gyeongsangbuk-do, South Korea
    • Yale University
      • Section of Cardiovascular Medicine
      New Haven, Connecticut, United States
    • Kangbuk Samsung Hospital
      Sŏul, Seoul, South Korea
    • Kyungpook National University Hospital
      Sŏul, Seoul, South Korea
  • 2002-2015
    • Chonbuk National University
      • • Department of Polymer Nano Science & Technology
      • • Division of Advanced Materials Engineering
      Tsiuentcheou, Jeollabuk-do, South Korea
  • 2013-2014
    • University of Ulsan
      • Department of Nursing
      Ulsan, Ulsan, South Korea
    • University of Akron
      • College of Polymer Science and Polymer Engineering
      Akron, Ohio, United States
    • Southern Illinois University Carbondale
      Illinois, United States
  • 2001-2014
    • Pusan National University
      • • Department of Laboratory Medicine
      • • Division of Electrical and Electronics Engineering
      Busan, Busan, South Korea
  • 2006-2013
    • Sungkyunkwan University
      • • Institute of Basic Science
      • • Department of Physics
      Sŏul, Seoul, South Korea
  • 2003-2012
    • Hongik University
      • Department of Chemical Engineering
      Sŏul, Seoul, South Korea
  • 2011
    • Ewha Womans University
      Sŏul, Seoul, South Korea
  • 2009-2011
    • Catholic University of Daegu
      • Department of Ophthalmology
      Kayō, Gyeongsangbuk-do, South Korea
  • 2008-2011
    • University of Texas at Austin
      • School of Nursing
      Austin, Texas, United States
    • Korea Photonics Technology Institute
      Sŏul, Seoul, South Korea
    • Inha University Hospital
      Sinhyeon, Gyeongsangnam-do, South Korea
  • 2005-2011
    • Gwangju Institute of Science and Technology
      • Department of Life Sciences
      Gwangju, Gwangju, South Korea
    • Seoul National University Hospital
      • • Department of Radiation Oncology
      • • Department of Thoracic and Cardiovascular Surgery
      Sŏul, Seoul, South Korea
  • 2010
    • Catholic Sangji College
      Antō, North Gyeongsang, South Korea
  • 2005-2009
    • Seoul National University
      • • College of Veterinary Medicine
      • • Department of Agricultural Biotechnology
      Sŏul, Seoul, South Korea
    • Inha University
      • College of Medicine
      Chemulpo, Incheon, South Korea
  • 2007
    • National Institutes of Health
      Maryland, United States
  • 2004
    • CHA University
      • College of Medicine
      Sŏul, Seoul, South Korea
  • 2000-2001
    • Hong-ik university
      United States
  • 1998
    • Samsung Advanced Institute of Technology
      Usan-ri, Gyeonggi Province, South Korea
  • 1996
    • Kent State University
      • Liquid Crystal Institute
      Kent, OH, United States
  • 1989
    • Jeonju National University of Education
      Tsiuentcheou, North Jeolla, South Korea