Ho Suk Lee

Kyungpook National University, Daikyū, Daegu, South Korea

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Publications (15)23.78 Total impact

  • Seok Cheol Choi · Ho Suk Lee · Sang Ho Sohn
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    ABSTRACT: The surface of light scattering TiO2 particles in the dye-sensitized solar cell (DSSC) was dual-coated with Al2O3 and SiO2 nanoparticles. The surface modification of the light scattering TiO2 particles was performed by a modified sol–gel method using the colloidal alumina and the colloidal silica as surface coating precursors. It was revealed that the dual-coated light scattering TiO2 particles leads to an increase in short-circuit photocurrent of DSSC device, resulting in an increase in energy conversion efficiency. This seems to be due to the increase of the light scattering by a combination of the light scattering TiO2 particles and the oxide nanoparticles such as Al2O3 and SiO2.
    No preview · Article · Nov 2012 · Advanced Powder Technology
  • Ho Suk Lee · Seok Cheol Choi · Sang Ho Sohn
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    ABSTRACT: A light scattering TiO2 layer was investigated in dye-sensitized solar cells. To enhance the efficiency by light scattering layer in DSSCs, surfaces of the light scattering TiO2 particles were modified by thin oxide layer such as Al2O3. The surface of the TiO2 powder was coated with Al2O3 nanoparticles using simple methods, which was a kind of the modified sol-gel method. The Al2O3-coated TiO2 powder was characterized by SEM and XRF. The overall conversion efficiency of the DSSCs with the Al2O3-coated TiO2 light scattering layer increased from 5.07% to 6.46% compared to the DSSCs with the non-coated one.
    No preview · Article · Oct 2012 · Molecular Crystals and Liquid Crystals
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    ABSTRACT: Multi-layered light scattering layer has been designed to improve the energy conversion efficiency of dye-sensitized solar cells (DSSCs) by scattering of the incident light. To enhance the light scattering properties, the surface of light scattering TiO2 particle was dual-coated with nano-sized Al2O3 and SiO2 particles by using a modified sol-gel method. Four kinds of the TiO2 electrodes with different thicknesses were fabricated and their photovoltaic effects on DSSCs were investigated. By increasing the thickness of light scattering layer, the total reflectance of working electrodes increased to 37%, resulting in an increase in the energy conversion efficiency up to 6.76%.
    No preview · Article · Oct 2012 · Molecular Crystals and Liquid Crystals
  • Seok Cheol Cho · Ho Suk Lee · Sang Ho Sohn
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    ABSTRACT: In this study, we prepared ZnO nanorods by a sonochemical method using a zinc acetate dihydrate as a new precursor. Well-aligned high-quality ZnO nanorods were synthesized on FTO glass by the sonochemical decomposition of zinc acetate dihydrate using a ZnO thin-film as the catalytic layer. The ZnO thin-films were deposited on the FTO glass by a sputtering method. To investigate their catalytic effects on the ZnO nanorods, catalytic ZnO thin-films of 20 nm, 40 nm, and 60 nm thickness were prepared by adjusting the sputtering time. The ZnO nanorods grown on catalytic layers with different thicknesses were characterized by SEM, XRD, and PL. The ZnO nanorods grown on the catalytic layer of 40 nm thickness show the best crystal and spatial orientation and as a result display the best optical properties. It was found that a catalytic ZnO thin-film of 40 nm in thickness yields well-aligned high-quality ZnO nanorods, due to its small surface roughness and structural strain.
    No preview · Article · Jul 2012 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: Laparoscopic resection for colorectal cancer has become popular. However, no previous studies have compared the laparoscopic and open approaches for colorectal cancer adherent to adjacent organs. This study analyzed the short- and long-term survival outcomes after laparoscopic multivisceral resection of the locally advanced primary colorectal cancer compared with open procedure in an effort to address appropriate patient selection. From a prospectively collected database, 54 patients with locally advanced primary colorectal cancer who had undergone multivisceral resection from March 2001 to September 2009 were identified. Laparoscopic and open surgeries were selectively performed for 38 and 16 patients, respectively. The two groups had similar demographics, with no differences in age, sex, and comorbidity. However, five emergency or urgency operations were included in the open group. No differences existed between the two groups in terms of tumor node metastasis (TNM) staging, histologic tumor infiltration rates, or curative resection rates. Three patients (7.9%) in the laparoscopic group required conversion to open procedure. In the laparoscopic group, the operation time was longer (330 vs. 257 min; p = 0.018), the volume of blood loss was less (269 vs. 638 ml; p = 0.000), and the time until return of bowel movement was shorter (3.7 vs. 4.7 days; p = 0.029) than in the open group. The perioperative morbidity rates were similar in the two groups (21.1% vs. 43.7%; p = 0.107), and no perioperative mortality occurred in either group. The mean follow-up period after curative resection was 40 months in the laparoscopic group and 35 months in the open group. The two groups showed similar rates for local recurrence (7.7% vs. 27.3%; p = 0.144) and distant metastasis (15.4% vs. 45.5%; p = 0.091). The overall 5-year survival rate was 60.5% for the laparoscopic group and 47.7% for the open group (p = 0.044, log-rank test). In terms of TNM stages, the overall 5-year survival rate for pathologic stage 3 disease was 58.3% for the laparoscopic group and 25% for the open group (p = 0.022, log rank test), but no difference was noted for the stage 2 patients (p = 0.384). No adverse long-term oncologic outcomes of laparoscopic resection were observed in this study. Although inherent limitations exist in this nonrandomized study, laparoscopic multivisceral resection seems to be a feasible and effective treatment option for colorectal cancer for carefully selected patients. Patients with colon cancer should be much more carefully selected for laparoscopic multivisceral resection than patients with rectal cancer because anatomic uncertainty can make oncologic en bloc resection incomplete.
    No preview · Article · Feb 2012 · Surgical Endoscopy
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    ABSTRACT: The effect of light scattering TiO2 particles surface-modified by Al2O3 coating on the characteristics of a dye-sensitized solar cell (DSSC) has been studied in this paper. The surface of the light scattering TiO2 particles was coated with Al2O3 by a modified sol–gel method as a function of the pH and the concentration of colloidal Al2O3. It was revealed that the uniform distribution of Al2O3 nanoparticles leads to an increase in short-circuit photocurrent of the DSSC device, resulting in an increase in energy conversion efficiency. This seems to be due to the increase in light scattering by the combination of the light scattering TiO2 particles and Al2O3 nanoparticles.
    Preview · Article · Feb 2012 · Physica Scripta
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    ABSTRACT: Spectroscopic ellipsometry was applied to study electro-optic effect in lead zirconate titanate^ (PZT) thin films grown epitaxially on Nb-doped SrTiO3(001) substrates by^ RF magnetron sputtering. Multilayer model analysis was applied^ to extract the ordinary and extraordinary refractive indices of the PZT thin film with electric^ field applied along the (001) direction. The effective linear and^ quadratic coefficients at a wavelength of 632.8 nm were estimated to be -134.6x10-12 m/V and 8.5x10-18 m^2/V^2, respectively, while the individual linear electro-optic^ coefficients r33 and r13 were -157.1 and 22 pm/V, respectively. We attributed existence of the linear electro-optic effect in unpoled PZT^ films to the presence of a built-in polarization^ and simultaneous poling during ellipsometric measurements.
    No preview · Article · Mar 2009
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    ABSTRACT: Using spectroscopic ellipsometry electro-optic effect was studied in lead zirconate titanate (PZT) thin films grown epitaxially on Nb-doped SrTiO <sub>3</sub>(001) substrates by RF magnetron sputtering. A uniaxial multilayer model analysis was applied to extract the linear and quadratic electro-optic coefficients from the shifts in the ordinary and extraordinary refractive indices with electric field applied along the (001) direction. The effective linear and quadratic coefficients were measured as -134.6×10<sup>-12</sup> m / V and 8.5×10<sup>-18</sup> m <sup>2</sup>/ V <sup>2</sup> , respectively, at a wavelength of 632.8 nm, while the individual linear electro-optic coefficients r<sub>33</sub> and r<sub>13</sub> were -157.1 and 22 pm/V, respectively. The existence of the linear electro-optic effect in unpoled PZT films was attributed to the presence of a built-in polarization and simultaneous poling during measurements.
    No preview · Article · Dec 2008 · Journal of Applied Physics
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    ABSTRACT: Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga/In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.
    No preview · Article · Aug 2007 · Applied Physics Letters
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    ABSTRACT: The purpose of this work is to investigate the effect of corona poling on the optical functions of the nonlinear-optical (NLO) polymers. We measured the complex refractive indices of NLO polymers deposited on glasses before and after corona poling using spectroscopic ellipsometry at room temperature at various incidence angles. In addition, we observed the absorption spectral change using ultraviolet-visible spectroscopy after corona poling, which is attributed to the chromophore orientation. In order to make NLO polymers, we attached a NLO active dye and photocrosslinkable moieties as side chains of poly(4-hydroxystyrene), deposited the polymer thin films on glass substrates by spin-coating, and corona-poled it along the surface-normal direction to align the dipoles of the chromophores along the electric field direction. In detail, PSDR1-25 designates a poly(4-hydroxystyrene) where 25% of hydroxyl groups in the side chain are substituted by disperse red 1 (DR1) and PSDR1-50 means the same except for 50% substitution. PSDR1 has the second-order NLO property, which is expected to show an acentric ordering by poling electric field. We used a parametric optical constant model to estimate the complex refractive index of the polymers. We found that the poling induced the uniaxial property of the complex refractive index of the polymers by aligning the chromophores along the poling direction. With increased poling voltage, we found that the oscillator strength of the major peak near the 2.4 eV (designated as E<sub>a</sub> ) peak decreases in the surface-parallel direction (x) , whereas that of the surface-normal direction (z) increases. Moreover, a detailed analysis of the dielectric functions using the standard critical point model showed that the poling induced a new peak E<sub>c</sub> (∼2.6 eV ) between dom- inant E<sub>a</sub> (∼2.3 eV ) and weak E<sub>b</sub> (∼2.9 eV ) peaks for PSDR1-50 polymers. With increased poling voltage, the E<sub>c</sub> peak strength increased compared to those of E<sub>a</sub> and E<sub>b</sub> peaks. We tentatively attribute E<sub>c</sub> to lower symmetry, possibly Stark effect, induced in the chromophores by the corona poling.
    No preview · Article · Aug 2007 · Journal of Applied Physics
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    ABSTRACT: The purpose of this study is to evaluate the risk factors for clinical anastomotic leakage after laparoscopic resection for rectal cancer.
    Preview · Article · Apr 2007 · Journal of the Korean Society of Coloproctology
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    ABSTRACT: We grow Zn1−xMnxO/Al2O3 (0 ⩽ x ⩽ 0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5 eV. Using the model of Holden et al. [ T. Holden et al., Phys. Rev. B 56, 4037 (1997) ], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3 eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3 eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization.
    No preview · Article · Jun 2006 · Journal of Applied Physics
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    ABSTRACT: We grow Zn1-xMnxO/Al2O3 (0
    No preview · Article · Jan 2006 · Journal of Applied Physics

  • No preview · Article · Jan 2006
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    ABSTRACT: We measured the pseudo-dielectric functions of several nonlinear optical (NLO) polymeric systems using spectroscopic ellipsometry in the spectral range between 0.8 and 4.7 eV . We fabricated the thin films after doping the nonlinear optical active chromophores into amorphous polycarbonate to show good optical transparency. We measured the ultraviolet-visible absorption spectra of the NLO chromophores in the film state. In order to determine the dielectric functions, we employed the Bruggeman effective medium approximation, assuming a mixture of two phases: host and guest. We used the Cauchy model for the dielectric function of the host polymer and a parametric optical constant model for that of the guest chromophore. We discussed the variation of the dielectric functions and the transition energies for various host-guest systems. In the gradient donor structural chromophores, we observed a decrease of the highest occupied molecular orbital (HOMO) lowest-unoccupied-molecular-orbital (LUMO) transition energy, and found a transition at about 3 eV . The decrease of HOMO—LUMO transition energy is attributed to the increase of electron donability and conjugative effect. We could fit the volume fractions of host and guest using spectroscopic ellipsometry, and compared them with the values estimated from the chemical structures of the molecules.
    No preview · Article · May 2005 · Journal of Applied Physics

Publication Stats

76 Citations
23.78 Total Impact Points

Institutions

  • 2012
    • Kyungpook National University
      • Department of Physics
      Daikyū, Daegu, South Korea
  • 2007-2012
    • Seoul Veterans Hospital
      Sŏul, Seoul, South Korea
  • 2005-2008
    • Kyung Hee University
      • Department of Physics
      Sŏul, Seoul, South Korea