Soyeon An

Inha University, Sŏul, Seoul, South Korea

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Publications (34)47.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The NO2 gas sensing properties of ZnGa2O4–TiO2 heterostructure nanorods was examined. ZnGa2O4-core/TiO2-shell nanorods were fabricated by the thermal evaporation of a mixture of Zn and GaN powders and the sputter deposition of TiO2. Multiple networked ZnGa2O4-core/TiO2-shell nanorod sensors showed the response of 876% at 10 ppm NO2 at 300°C. This response value at 10 ppm NO2 is approximately 4 times larger than that of bare ZnGa2O4 nanorod sensors. The response values obtained by the ZnGa2O4-core/TiO2-shell nanorods in this study are more than 13 times higher than those obtained previously by the SnO2-core/ZnO-shell nanofibers at 5% NO2. The significant enhancement in the response of ZnGa2O4 nanorods to NO2 gas by coating them with TiO2 can be explained based on the space-charge model.
    Journal of Nanoscience and Nanotechnology 01/2015; 15(1). · 1.15 Impact Factor
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    ABSTRACT: TeO2 nanorods functionalized with Co3O4 nanoparticles were fabricated using thermal evaporation and hydrothermal methods. X-ray diffraction and transmission electron microscopy showed that the cores and shells were single crystal TeO2 and polycrystalline Co3O4, respectively. The multiple networked TeO2/Co3O4 composite nanorod sensor showed responses of 333–1,276%, response times (75–110 sec), and recovery times (20–40 sec) ethanol (C2H5OH) concentrations of 50–250 ppm at 300°C. The response values are 3–10 times higher and the response and recovery times are also far shorter than those of the pristine TeO2 nanorod sensor over the same C2H5OH concentration range. The origin of the enhanced ethanol sensing properties of the composite nanorod sensor is discussed.
    Journal of Nanoscience and Nanotechnology 01/2015; 15(1). · 1.15 Impact Factor
  • 02/2014;
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    ABSTRACT: Au-functionalized ZnO nanorods were synthesized by carbothermal evaporation of a mixture of ZnO and graphite powders at 900 °C followed by gold (Au) sputter-deposition and thermal annealing. The ZnO nanorods had a rod-like morphology with relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 100 nm and 3–4 μm, respectively. The diameters of the Au particles on the nanorods ranged from 5 to 40 nm. The dependence of the photoluminescent properties of Au-functionalized ZnO nanorods on the postannealing atmosphere was examined. Annealing resulted in an increase and decrease in the near-band edge (NBE) and deep level (DL) emission intensities of Au-coated ZnO nanorods, respectively, whereas both the NBE and DL emission intensities of uncoated ZnO nanorods were increased by annealing. The intensity ratio of NBE emission to DL emission of the Au-capped ZnO nanorods was increased ~25 fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Au-capped ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Au.
    Journal of Luminescence 01/2014; 147:5–8. · 2.14 Impact Factor
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    ABSTRACT: WO3 nanotubes were synthesized using TeO2 nanowire templates. Transmission electron microscopy revealed the nanotubes to have tube diameters, lengths, and wall thicknesses ranging from 100–200 nm, 3–4 μm, and 20–30 nm, respectively. The multiple networked WO3 nanotube sensors showed responses of 144–677% in the NO2 concentration range of 1–5 ppm at 300 °C. These responses were approximately double those observed for the WO3 nanorod sensors over the same NO2 concentration range. A model describing the gas sensing mechanism of WO3 NTs is also proposed.
    Ceramics International 01/2014; 40(1):1423–1429. · 1.79 Impact Factor
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    ABSTRACT: Au-functionalized ZnSe nanorods were synthesized by the thermal evaporation of ZnSe powder followed by Au sputter-deposition and thermal annealing. Photoluminescence (PL) showed that the intensity of near-band edge (NBE) emission of ZnSe nanorods was enhanced remarkably by Au-coating and annealing in a H2 atmosphere. The intensity ratio of NBE emission to the deep level emission, INBE/IDL of Au-coated ZnSe nanorods after annealing in a H2 atmosphere was ∼68 times higher than that of the pristine (unannealed, uncoated) ZnSe nanorods. The increase in INBE/IDL might be due to a combination of carrier transfer from the defect level to the Fermi level of Au nanoparticles, surface plasmon resonance in Au nanoparticles and hydrogen passivated deep level defects.
    Materials Chemistry and Physics 01/2014; 143(2):735–739. · 2.07 Impact Factor
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    ABSTRACT: TeO2-core/TiO2-shell nanowires were fabricated by thermal evaporation of Te powders and MOCVD of TiO2. The as-synthesized TeO2 nanowires showed a weak broad violet band centered at approximately 430 nm. The emission peak was shifted to a bluish violet region (˜455 nm) by the encapsulation of the nanowires with a TiO2 thin film. The intensity of the major emission from the core-shell nanowires showed strong dependence on the shell layer thickness. The strongest emission was obtained for the shell layer thickness of ˜15 nm and its intensity was approximately 80 times higher than that of the violet emission from the as-synthesized TeO2 nanowires. This enhancement in emission intensity is attributed to the subwavelength optical resonant cavity formation in the shell layer. The major emission intensity was enhanced further and blue-shifted by annealing, which might be attributed to the increase in the Ti interstitial and O vacancy concentrations in the TeO2 cores during annealing.
    Physica E Low-dimensional Systems and Nanostructures 12/2013; · 1.86 Impact Factor
  • Thin Solid Films 11/2013; · 1.87 Impact Factor
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    ABSTRACT: Zinc sulfide (ZnS) nanostructures with different morphologies and microstructures were synthesized using a single thermal evaporation process. The microstructure and photoluminescence properties of the ZnS nanowires produced in four different temperature zones were examined. Scanning electron microscopy showed that as the substrate temperature decreased, the morphology of the ZnS nanowires changed from a longer curved morphology to a shorter earthworm-like morphology. X-ray diffraction (XRD) shows that all samples were mixtures of a zincblende-structured ZnS phase and a wurtzite-structured ZnS phase and that dominance of the zincblende phase tends to increase with decreasing substrate temperature. The zincblende phase appeared to be dominant regardless of the substrate temperature. A closer comparison of the XRD patterns of the products in the different temperature zones showed that dominance of the zincblende phase tends to increase with decreasing substrate temperature. Photoluminescence spectroscopy revealed a decrease in emission intensity with decreasing substrate temperature. ZnS nanostructures synthesized in temperature zones 2, 3 and 4 (∼ 900, ∼ 800 and ∼ 700 °C, respectively) showed green emission, whereas those synthesized in temperature zone 5 (∼ 600 °C) showed yellow emission. The origins of the emissions are also discussed.
    Physica Scripta Volume T. 11/2013;
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    ABSTRACT: TiO2-core/ZnO-shell nanorods were synthesized using a two-step process: the synthesis of TiO2 nanorods using a hydrothermal method followed by atomic layer deposition of ZnO. The mean diameter and length of the nanorods were ˜300 nm and ˜2.3 μm, respectively. The cores and shells of the nanorods were monoclinic-structured single-crystal TiO2 and wurtzite-structured single-crystal ZnO, respectively. The multiple networked TiO2-core/ZnO-shell nanorod sensors showed responses of 132-1054 % at ethanol (C2H5OH) concentrations ranging from 5 to 25 ppm at 150 ∘C. These responses were 1-5 times higher than those of the pristine TiO2 nanorod sensors at the same C2H5OH concentration range. The substantial improvement in the response of the pristine TiO2 nanorods to C2H5OH gas by their encapsulation with ZnO may be attributed to the enhanced absorption and dehydrogenation of ethanol. In addition, the enhanced sensor response of the core-shell nanorods can be attributed partly to changes in resistance due to both the surface depletion layer of each core-shell nanorod and the potential barriers built in the junctions caused by a combination of homointerfaces and heterointerfaces.
    Applied Physics A 09/2013; · 1.69 Impact Factor
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    ABSTRACT: In2O3 nanotubes were synthesized as gas sensors using TeO2 nanowires as a template. Scanning and transmission electron microscopy revealed the tubes to have diameters of a few hundred nanometers, wall thickness of ∼25 nm and lengths up to a few millimeters. Multiple networked Au-doped In2O3 nanotube sensors showed responses of 187–1219% to 50–250 ppm C2H5OH at 300 °C. These responses are far superior to those obtained by undoped In2O3 nanotubes and stronger than those obtained by pure In2O3 nanowires at 370 °C. In addition, the ethanol sensing mechanism of the Au-doped In2O3 nanotube sensors is discussed.
    Journal of Physics and Chemistry of Solids 07/2013; 74(7):979–984. · 1.53 Impact Factor
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    ABSTRACT: CuO/In2O3 core–shell nanorods were fabricated using thermal evaporation and radio frequency magnetron sputtering. X-ray diffraction and transmission electron microscopy showed that both the cores and shells were crystalline. The multiple networked CuO/In2O3 core–shell nanorod sensors showed responses of 382–804%, response times of 36–54 s and recovery times of 144–154 s at ethanol (C2H5OH) concentrations ranging from 50 to 250 ppm at 300 °C. These responses were 2.3–2.8 times higher than those of the pristine CuO nanorod sensor over the same C2H5OH concentration range. The origin of the enhanced ethanol sensing properties of the core–shell nanorod sensor is discussed.
    Ceramics International. 07/2013; 39(5):5255–5262.
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    ABSTRACT: TeO2/In2O3 core–shell nanorods were fabricated using thermal evaporation and sputtering methods. The multiple networked TeO2/In2O3 core–shell nanorod sensor showed responses of 227–632%, response times of 50–160 s, and recovery times of 190–220 s at ethanol (C2H5OH) concentrations of 50–250 ppm at 300 °C. The response values are 1.6–2.9 times higher and the response and recovery times are also considerably shorter than those of the pristine TeO2 nanorod sensor over the same C2H5OH concentration range. The origin of the enhanced ethanol sensing properties of the core–shell nanorod sensor is discussed.
    Current Applied Physics 07/2013; 13(5):919–924. · 2.03 Impact Factor
  • Current Applied Physics 07/2013; · 2.03 Impact Factor
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    ABSTRACT: Zn2SnO4-core/ZnO-shell nanorods were synthesized using a two-step process: synthesis of Zn2SnO4 nanorods the thermal evaporation of a mixture of ZnO, SnO2, and graphite powders, followed by atomic layer deposition (ALD) of ZnO. The nanorods were 50–250 nm in diameter and a few to a few tens of micrometers in length. The cores and shells of the nanorods were face-centered cubic-structured single crystal Zn2SnO4 and wurtzite-structured single crystal ZnO, respectively. The multiple networked Zn2SnO4-core/ZnO-shell nanorod sensors showed a response of 173–498% to NO2 concentrations of 1–5 ppm at 300 °C. These response values are 2–5 times higher than those of the Zn2SnO4 nanorod sensor over the same NO2 concentration range. The NO2 sensing mechanism of the Zn2SnO4core/ZnO-shell nanorods is discussed.
    Ceramics International. 05/2013; 39(4):3539–3545.
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    ABSTRACT: Gas sensors based on Ag–TeO2 composite nanorods were fabricated using thermal evaporation and sputtering techniques. The morphology, structure and phase composition of the as-prepared nanofibers were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD), respectively. TEM and XRD showed that the nanorods and nanoparticles on them were tetragonal-structured single crystal TeO2 and a mainly amorphous phase, respectively. The multiple-networked bare TeO2 nanorod sensors exhibited a response of ∼219% at 25 ppm C2H5OH at 300 °C, whereas the Ag-functionalized TeO2 nanorod sensors showed a response of ∼808% under the same conditions. The mechanism by which the sensing properties of the TeO2 nanorods were enhanced by functionalization with Ag is also discussed.
    Current Applied Physics 05/2013; 13(3):576–580. · 2.03 Impact Factor
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    ABSTRACT: Zn2SnO4-core/ZnO-shell nanorods were synthesized using a two-step process: synthesis of Zn2SnO4 nanorods the thermal evaporation of a mixture of ZnO, SnO2, and graphite powders, followed by atomic layer deposition (ALD) of ZnO. The nanorods were 50–250 nm in diameter and a few to a few tens of micrometers in length. The cores and shells of the nanorods were face-centered cubic-structured single crystal Zn2SnO4 and wurtzite-structured single crystal ZnO, respectively. The multiple networked Zn2SnO4-core/ZnO-shell nanorod sensors showed a response of 173–498% to NO2 concentrations of 1–5 ppm at 300 °C. These response values are 2–5 times higher than those of the Zn2SnO4 nanorod sensor over the same NO2 concentration range. The NO2 sensing mechanism of the Zn2SnO4core/ZnO-shell nanorods is discussed.
    Ceramics International. 05/2013; 39(4):3539–3545.
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    ABSTRACT: ZnGa2O4 nanowires were synthesized using a thermal evaporation technique. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction revealed that the nanowires were single crystals 30–200 nm in diameter and ranged up to ∼100 μm in length. The sensing properties of multiple networked ZnGa2O4 nanowire sensors functionalized with Au catalyst nanoparticles with diameters of a few nanometers toward NO2 gas at room temperature under UV irradiation were examined. The sensors showed a remarkably enhanced response and far reduced response and recovery times toward NO2 gas at room temperature under 254 nm-ultraviolet (UV) illumination. The response of ZnGa2O4 nanowires to NO2 gas at room temperature increased from ∼100 to ∼861 % with increasing the UV intensity from 0 to 1.2 mW/cm2. The significant improvement in the response of ZnGa2O4 nanowires to NO2 gas by UV irradiation is attributed to the increased change in resistance due to the increase in the number of electrons participating in the reactions with NO2 molecules by photo-generation of electron–hole pairs.
    Applied Physics A 05/2013; · 1.69 Impact Factor
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    ABSTRACT: SnO2-core/ZnO-shell nanowires were synthesized using a two-step process: the synthesis of SnO¬2¬ nanowires by the thermal evaporation of Sn powders followed by the atomic layer deposition of ZnO. The room temperature NO2 gas sensing properties of the nanowires under ultraviolet (UV) irradiation were examined. The cores and shells of the nanowires were primitive tetragonal-structured single crystal SnO2 and wurtzite-structured single crystal ZnO, respectively. The responses of the multiple networked SnO¬2 nanowire sensors were increased 2-3 fold at NO2 concentrations ranging from 1 to 5 ppm by encapsulating the nanowires with ZnO. The SnO2-core/ZnO-shell nanowire sensors showed a remarkably enhanced response under UV illumination. The sensing mechanism of the core-shell nanowires under UV illumination is also discussed.
    ACS Applied Materials & Interfaces 04/2013; · 5.90 Impact Factor
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    ABSTRACT: one-dimensional (1D) nanostructures were synthesized by using a thermal evaporation technique. The morphology, crystal structure, and sensing properties of the nanostructures functionalized with Pt to gas at room temperature under UV irradiation were examined. The diameters of the 1D nanostructures ranged from a few tens to a few hundreds of nanometers and the lengths ranged up to a few hundreds of micrometers. Pt nanoparticles with diameters of a few tens of nanometers were distributed around a nanorod. The responses of the nanorods gas sensors fabricated from multiple networked nanorods were improved 3-4 fold at concentrations ranging from 1 to 5 ppm by Pt functionalization. The Pt-functionalized nanorod gas sensors showed a remarkably enhanced response at room temperature under ultraviolet (UV) light illumination. In addition, the mechanisms via which the gas sensing properties of nanorods are enhanced by Pt functionalization and UV irradiation are discussed.
    Bulletin- Korean Chemical Society 01/2013; 34(6). · 0.84 Impact Factor