S. H. Kim

Pohang University of Science and Technology, Andong, North Gyeongsang, South Korea

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Publications (57)98.03 Total impact

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    ABSTRACT: High quality Zn1−xFexO thin films were deposited on α-sapphire substrates by RF magnetron sputtering. X-ray absorption fine structure measurements showed that the chemical valence of Fe ions in the films was a mixture of 2+ and 3+ states, and Fe ions substituted mainly for the Zn sites in the films. DC-magnetization measurements revealed ferromagnetic properties from 5 to 300 K. The photoluminescence measurements at 15 K showed a sharp main transition peak at 3.35 eV along with a broad impurity peak at 2.45 eV. The structural and magnetization analyses of the Zn1−xFexO films strongly suggested that the ferromagnetism was the intrinsic properties of the films.
    Journal of Crystal Growth 07/2010; 312(14):2093-2097. · 1.69 Impact Factor
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    ABSTRACT: Vertically-well-aligned ZnO nanorods were synthesized on Ti buffer layers by a metal-organic chemical-vapor deposition process. Structural analyses demonstrated that the ZnO nanorods were well-aligned in the c-axis and ab-plane. Transmission electron microscopy (TEM) showed that the Ti buffer layer was amorphous and interdiffused into the ZnO nanorods. Energy-dispersive spectroscopy (EDS) analysis revealed the Ti buffer layers to be slightly oxide. Extended x-ray absorption fine structure confirmed the TEM and EDS results. The I-V characteristic measurements showed a 20-fold increase in current density with the Ti buffer layer, suggesting excellent electrical contact between the Ti buffer layer and ZnO nanorods.
    Applied Physics Letters 02/2010; 96(5):051908-051908-3. · 3.52 Impact Factor
  • DN Kang, KI Jung, SH Kim, SH Jeon
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    ABSTRACT: Neurogenesis in Drosophila melanogaster is initiated by an ordered appearance of neuroblasts arranged in three columns (medial, intermediate, and lateral) in the neuroectoderm. In each column, specific homeodomain-containing genes are expressed. The ventral nervous system defective (vnd) regulates the fate of the cells in the medial domain of the neuroectoderm. In the present study, we identified Vnd-regulated genes through computational screening. Through further screening, we selected eight genes that were downregulated in the vnd loss-of function mutation. These included zfh1, uzip, CG7687, SytIV, stau, ase, scrt, and dpn genes. Ectopic expression of vnd, using the GAL4/UAS system, caused abnormal expression of all eight genes. Further, eight genes were coexpressed with that of vnd. Reverse-transcriptase polymerase chain reaction (RT-PCR) experiments showed an enhanced expression of uzip, CG7687, SytIV, and ase. Although the other four genes did not show an enhanced expression through RT-PCR, cytochemical and genetic evidence showed that these genes were regulated by Vnd. Taken together, the results obtained from this study indicate that expression of at least four genes, uzip, CG7687, SytIV, and ase, are regulated by Vnd.
    Journal of neurogenetics 05/2009; · 0.73 Impact Factor
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    ABSTRACT: This study reports the structural and the magnetic properties of Zn1xFexO (ZnFeO) lms with Fe composition ratios of 0.03 { 0.07. High-quality Zn1xFexO thin lms with a mean thickness of 500 nm were fabricated on -sapphire (0001) substrates by RF magnetron sputtering. The structures of the ZnFeO thin lms were examined using various techniques. X-ray diraction revealed the lms to have a well-ordered wurtzite structure without any extra phases. However, the ZnO (0002) diraction peak shifted gradually from 2 = 34.378 to 34.142 with increasing Fe concentration from 0.03 to 0.07. This corresponds to a lattice constant increase of 0.035 A. X-ray photoelectron spectroscopy (XPS) measurements were employed to characterize the valence state of the Fe ions in the lms. The XPS revealed the coexistence of Fe 3+ and Fe 2+ ions in the lms. The DC-magnetization measurements demonstrated that the ZnFeO lms were ferromagnetic at 5 K.
    Journal- Korean Physical Society 04/2008; 52. · 0.43 Impact Factor
  • Advanced Materials 12/2006; 19(1):73 - 76. · 15.41 Impact Factor
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    ABSTRACT: Acute renal failure (ARF) with severe loin pain induced by anaerobic exercise is a rare condition that is accompanied by wedge-shaped contrast enhancement seen on computerized tomographic (CT) scan without evidence of rhabdomyolysis. An 18-year-old Korean male was transferred to our hospital for evaluation of mild azotemia, that developed after anaerobic exercise. The laboratory tests revealed that the serum creatinine was 2.1 mg/dl and the serum uric acid level was 1.6 mg/dl without any elevation of the serum myoglobin or creatine phosphokinase. Under the impression of exercise-induced ARF, we tried to determine the relationship between the occurrence of clinical symptoms, renal dysfunction and the characteristic CT findings by observing those changes prospectively before and after anaerobic exercise. After obtaining a written consent, the patient underwent a strenuous period of anaerobic exercise to induce the clinical symptoms. Before exercise, he was completely asymptomatic; his serum creatinine level was 0.9 mg/dl and CT scan of the kidneys showed no abnormalities. Loin pain developed 2 hours after exercise, and the serum creatinine level increased to 1.2 mg/dl 18 hours after the exercise. CT scan 18 hours after exercise showed multiple perfusion defects, and a 24-hour delayed CT scan showed multiple areas of wedge-shaped enhancement on both kidneys. These changes were completely resolved on the follow-up CT scan obtained 13 days after exercise with the return of a normal serum creatinine level. We conclude that reversible renal vasoconstriction is probably the main pathophysiologic mechanism of acute renal failure induced by anaerobic exercise.
    Clinical nephrology 11/2006; 66(4):297-301. · 1.23 Impact Factor
  • Journal of Materials Science 08/2006; 41(18):6081-6086. · 2.31 Impact Factor
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    ABSTRACT: The possibility of synthesis of quasicrystalline and associated approximant phases during mechanical alloying and subsequent heat treatment of Al65Cu20Fe10Si5 alloy powders has been investigated. It is shown that, in addition to the stable ordered quasicrystal and 1/1 cubic approximant, two more phases having orthorhombic symmetry coexist. The a and c parameters of both these phases are similar to the lattice parameters of the cubic approximant, whereas their b parameters are, respectively, three and four times larger than the c parameters. It is suggested that these phases evolve on account of local symmetry breaking of the cubic approximant phase, possibly due to ordering.
    Philosophical Magazine Letters 07/2006; 86(7):425-433. · 1.27 Impact Factor
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    ABSTRACT: The mechanism for ion-induced uniaxial magnetic anisotropy of ferromagnetic CoPt thin films is investigated using x-ray diffraction and soft x-ray emission spectroscopy. When Co/Pt multilayers 64 nm thick are irradiated with 80 keV Ar+ ions in an externally applied magnetic field, the magnetization of the ion-irradiated area shows a significant anisotropic angular dispersion in its hysteresis. Analysis of x-ray diffraction patterns and Co L3 emission spectra reveals that the formation of partially ordered (face-centered-tetragonal) CoPt phase and nonequivalent electronic hybridization between easy and hard axes causes the induction of a uniaxial magnetic anisotropy.
    Applied Physics Letters 02/2006; 88:092504. · 3.52 Impact Factor
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    ABSTRACT: We present the structural and optical properties of Zn1−xMgxO thin films studied using x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS), and photoluminescence (PL) measurements. The Zn1−xMgxO films on sapphire [0001] substrates were fabricated with metal organic chemical vapor deposition (MOCVD). The XRD measurements showed that the Zn1−xMgxO films (x≤0.05) had a wurtzite structure without any MgO phase and were epitaxially grown along the c-axis of the Al2O3 substrate. The lattice constant of the Zn0.95Mg0.05O film shrank by 0.023 Å, compared with that of ZnO crystals. From the EXAFS measurements on the Zn1−xMgxO films at Zn K-edge, we found a substantial amount of distortion in the bond length of Zn-Zn pairs with a small amount of Mg substitution on the Zn site. The PL measurements showed a gradual increment of the main exciton transitions from 3.36 eV (x=0.0) to 3.57 eV (x=0.05) at 10 K. We also observed a strong deep-level emission near 2.3 eV from the specimen with x=0.05.
    Journal of Electronic Materials 01/2006; 35(8):1680-1684. · 1.68 Impact Factor
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    ABSTRACT: We investigated resistance switching in top-electrode/ Ni O / Pt structures where the top electrode was Au, Pt, Ti, or Al. For Pt / Ni O / Pt and Au / Ni O / Pt structures with ohmic contacts, the effective electric field inside the film was high enough to induce trapping or detrapping at defect states and thus resistance switching. For a Ti / Ni O / Pt structure with well-defined Schottky contact at Ti / Ni O interface accompanied by an appreciable voltage drop, the effective electric field inside the NiO film was not enough to induce resistance switching. For an Al / Ni O / Pt structure with a low Schottky barrier at the Al / Ni O interface, resistance switching could be induced at a higher voltage since the voltage drop at the Al / Ni O interface was not negligible but small.
    Applied Physics Letters 01/2006; · 3.52 Impact Factor
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    ABSTRACT: We demonstrate room-temperature low-threshold-current lasing action from electrically driven wavelength-scale high-quality photonic crystal lasers having large spontaneous emission factors by solving the theoretical and technical constraints laid upon by the additional requirement of the current injection. The ultrasmall cavity is electrically pulse pumped through a submicron-size semiconductor “wire” at the center of the mode with minimal degradation of the quality factor. In addition, to better utilize the low mobility of the hole, we employ a doping structure that is inverted from the conventional semiconductors. Rich lasing actions and their various characteristics are experimentally measured in the single-cell and three-cell photonic crystal cavities. Several relevant measurements are compared with three-dimensional finite-difference time-domain computations based on the actual fabricated structural parameters. The electrically driven photonic crystal laser, which is a small step toward a “practical” form of the single photon source, represents a meaningful achievement in the field of photonic crystal devices and photonic integrated circuits as well as of great interest to the quantum electrodynamics and quantum information communities.
    IEEE Journal of Quantum Electronics 10/2005; · 2.11 Impact Factor
  • Journal- Korean Physical Society 09/2005; 47(92):243-. · 0.43 Impact Factor
  • Journal- Korean Physical Society 09/2005; 47(92):247-. · 0.43 Impact Factor
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    ABSTRACT: Wideband mobile radio channel characteristics were measured in various environments in Korea. SKT conducted impulse response measurements at 2.3 GHz with a commercial channel sounder and presents multipath channel models for wireless local and metropolitan area networks. In this paper, we describe the process to analyze the measured data and build tapped delay line channel models. The whole measurements were conducted throughout more than 25 sites around Seoul city and various channel models that represents rural, suburban, suburban alternative, micro-cell hilly, urban high-rise and urban rooftop environments are presented.
    Information Technology and Applications, 2005. ICITA 2005. Third International Conference on; 08/2005
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    ABSTRACT: We present a systematic study of the hydrogen induced anomalous expansion of the top layer spacing, d12, using low-energy electron diffraction and surface x-ray scattering. After exposure of 6 L of hydrogen at 150 K sample temperature, the hydrogen atoms fully occupy the surface hollow sites and a lattice expansion of Δd12=+4.7% is determined in agreement with theoretical predictions (5.2%). Heating the sample above the hydrogen desorption temperature (TD≈340 K), leads to an almost complete relaxation of d12 to the bulk value of 1.945 Å. Similarly, no expansion is observed for clean Pd(001) prepared by rapid cooling after quick thermal treatment to remove hydrogen. Hydrogen re-adsorption from the residual gas atmosphere and possibly hydrogen agglomeration in the near surface region leads to an expansion of d12 in the 2%–3% range as observed in previous experiments. On the basis of our results, surface magnetism as a mechanism to trigger lattice expansion in Pd(001) does not need to be invoked.
    Physical Review B 05/2005; 71(20). · 3.66 Impact Factor
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    ABSTRACT: We experimentally compare the performance of our proposed single pump, Raman/EDFA hybrid amplifiers recycling residual Raman pump in a cascaded EDF located either after or prior to a DCF with that of a Raman assisted EDFA, the concept of which was proposed by Y. Kurosawa et al. (Proc. European Conf. on Optical Comm. ECOC2003, Tu3.2.5, 2003) in terms of gain, NF, nonlinearity, and BER.
    Optical Fiber Communication Conference, 2005. Technical Digest. OFC/NFOEC; 04/2005
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    ABSTRACT: Conductivity switching phenomena controlled by external voltages have been investigated for various NiO films deposited by dc reactive sputtering methods. Pt/NiO/Pt capacitor structures with top electrodes of different diameters have showed increasing off-state current with the diameter of a top electrode and nearly the same on-state current independent of the diameter. Local conductivity switching behaviors have been observed in a series structure consisting of two Pt/NiO/Pt capacitors with different resistance values. By reasoning out conductivity switching mechanisms from the switching characteristics and introducing multilayers consisting of NiO layers with different resistance values, we have reduced the reset current by two orders of magnitude.
    Applied Physics Letters 02/2005; 86(9):093509-093509-3. · 3.52 Impact Factor
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    ABSTRACT: The atomic structures of clean and hydrogen-adsorbed Pd(001) are investigated by low energy electron diffraction (LEED) I/V analysis. Clean Pd(001) shows little surface relaxation in sharp contrast to previous reports. Adsorbing 1 monolayer of hydrogen on Pd(001), we observe sizable expansion of the interlayer spacing of the first two surface layers, $d_{12}$ by 4.7% of the corresponding one of bulk Pd. Both experimental observations are in excellent agreement with the predictions of recent {\it ab initio} calculations. A series of experiments with varying coverages of hydrogen adsorbed on Pd(001), reveals that $d_{12}$ monotonically increases with the increasing coverage. Such an observation strongly supports the contention that the previous observation of expanded $d_{12}$ in clean Pd(001) results from contamination of the surface by residual hydrogen.
    12/2004;
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    ABSTRACT: A flexibly-tunable multi-wavelength Raman fibre laser based on the polarisation maintaining fibre (PMF) Lyot-Sagnac filter after composing fibre Bragg grating cavity is demonstrated experimentally. The number of channels and wavelength spacing of the Raman laser can be controlled readily by Δn · L products of PMF segments in the intracavity PMF Lyot-Sagnac filter.
    Electronics Letters 12/2004; · 1.07 Impact Factor

Publication Stats

1k Citations
98.03 Total Impact Points

Institutions

  • 2006–2010
    • Pohang University of Science and Technology
      • Department of Materials Science and Engineering
      Andong, North Gyeongsang, South Korea
    • Incheon St. Mary’s Hospital, Catholic Medical Center
      Bucheon, Gyeonggi Province, South Korea
    • Kumoh National Institute of Technology
      Sŏul, Seoul, South Korea
  • 2004–2006
    • Konkuk University
      • School of Physics
      Sŏul, Seoul, South Korea
    • Max Planck Institute of Physics
      München, Bavaria, Germany
  • 1999–2006
    • Yonsei University
      • • Department of Physics
      • • Center for Noncrystalline Materials
      Seoul, Seoul, South Korea
  • 2005
    • Max Planck Institute of Microstructure Physics
      Halle-on-the-Saale, Saxony-Anhalt, Germany
  • 1999–2004
    • Chonnam National University
      • Department of Computer Science
      Gwangju, Gwangju, South Korea
  • 2001
    • Sungkyunkwan University
      • Department of Physics
      Seoul, Seoul, South Korea
    • Concordia University Montreal
      • Centre for Pattern Recognition and Machine Intelligence
      Montréal, Quebec, Canada
  • 1997
    • Hong-ik university
      United States