Soyeon An

Inha University, Sŏul, Seoul, South Korea

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Publications (37)78.72 Total impact

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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). DOI:10.1166/jnn.2015.8334 · 1.34 Impact Factor
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    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). DOI:10.1166/jnn.2015.8333 · 1.34 Impact Factor
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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 03/2014; 147:5–8. DOI:10.1016/j.jlumin.2013.10.044 · 2.37 Impact Factor
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    ABSTRACT: Pd-functionalized ZnS nanorods were prepared for use as gas sensors. Scanning electron microscopy revealed the diameters and lengths of the nanorods ranging from 30 to 80 nm and from 2 to 5 mu m, respectively. The diameter of Pd nanoparticles ranged from 2 to 5 nm. Transmission electron microscopy revealed that ZnS nanorods and Pd nanoparticles were monocrystalline and amorphous, respectively. The responses of multiple networked ZnS nanorods sensors to 1-5 ppm NO2 were increased substantially by a combination of Pd functionalization and UV irradiation. Pristine ZnS nanorod sensors at room temperature in the dark showed a response (similar to 100%) almost independent of NO2 concentration in a NO2 concentration range of 1-5 ppm. Pristine ZnS nanorod sensors showed enhanced responses of 214-603% to 1-5 ppm NO2 at room temperature under UV illumination. Pd-functionalized ZnS nanorods sensors showed further enhanced responses of 355-1511% to 1-5 ppm NO2 at room temperature under UV illumination. The NO2 gas sensing mechanism of the Pd-functionalized ZnS nanorods sensors under UV illumination is discussed in depth.
    Current Applied Physics 02/2014; 14. DOI:10.1016/j.cap.2013.11.041 · 2.03 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. DOI:10.1016/j.matchemphys.2013.10.007 · 2.13 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. DOI:10.1016/j.ceramint.2013.07.025 · 2.09 Impact Factor
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    ABSTRACT: Ag-decorated ZnO nanorods were synthesized by thermal evaporation of a mixture of ZnO and graphite powders at 900 °C followed by wet Ag coating and thermal annealing. The ZnO nanorods had a rod-like morphology with a relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 300 nm and up to a few hundred micrometers, respectively. The diameters of the Ag particles on the nanorods ranged from 10 to 100 nm. The dependence of the photoluminescence properties of Ag-decorated 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 Ag-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 Ag-coated ZnO nanorods was increased ~15-fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Ag-coated ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Ag.
    Journal of Materials Science Materials in Electronics 12/2013; 24(12). DOI:10.1007/s10854-013-1496-4 · 1.97 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; 54:5-8. DOI:10.1016/j.physe.2013.05.023 · 1.86 Impact Factor
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    ABSTRACT: ZnGa2O4 nanowires were synthesized on Si substrates by using the thermal evaporation of a mixture of Zn and GaN powders. Scanning electron microscopy showed that the diameters and the lengths of the nanowires ranged from a few tens to a few hundreds of nanometers and up to a few hundreds of micrometers, respectively. The ZnGa2O4 nanowires were found to have a face-centered cubic-structured monocrystalline phase. The photoluminescence properties of the ZnGa2O4 nanowires appeared to depend strongly on the annealing atmosphere. The ZnGa2O4 nanowires annealed in a hydrogen atmosphere showed a relatively weak broad visible emission band, ranging from 500 to 700 nm. In contrast, the ZnGa2O4 nanowires annealed in an oxygen atmosphere showed a relatively strong near-ultraviolet emission band centered at approximately 380 nm. On the other hand, the ZnGa2O4 nanowires annealed in an argon atmosphere showed a sharp, taller ultraviolet emission peak centered at approximately 380 nm, as well as a broad green emission band centered at approximately 510 nm. The origins of the enhanced luminescence in ZnGa2O4 nanowires due to annealing in different atmospheres are discussed.
    Journal- Korean Physical Society 12/2013; 63(12). DOI:10.3938/jkps.63.2367 · 0.43 Impact Factor
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    ABSTRACT: This paper reports the synthesis of ZnTe nanostructures with a range of morphologies and sizes using a novel, simple thermal evaporation technique and their luminescence properties. Photoluminescence measurements showed that pure ZnTe nanostructures synthesized at 600 degrees C by the thermal evaporation of ZnTe nanopowders had an intense emission band centered at similar to 810 nm, whereas those of the ZnTe nanostructures obtained at similar to 500 and similar to 700 degrees C showed weak emission bands centered at similar to 820 and similar to 880 nm, respectively. Energy-dispersive X-ray spectroscopy revealed that the intense near-infrared emission was attributed to localized states associated with zinc vacancies.
    Journal of Alloys and Compounds 12/2013; 580:316-320. DOI:10.1016/j.jallcom.2013.06.107 · 2.73 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.
    11/2013; T157:4043-. DOI:10.1088/0031-8949/2013/T157/014043
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    ABSTRACT: Au-functionalized ZnS nanowires were prepared for use as gas sensors. Scanning electron microscopy revealed the diameters and lengths of the nanowires ranging from 20 to 100 nm and from a few tens to a few hundreds of micrometers, respectively. X-ray diffraction and transmission electron microscopy revealed that ZnS nanowires and Au nanoparticles were monocrystalline and polycrystalline, respectively. The responses of multiple networked ZnS nanowire sensors to 1-5 ppm NO2 were increased 1.6- to 1.9-fold and 2.8- to 5.4-fold by Au functionalization and a combination of Au functionalization and UV irradiation, respectively. Au-functionalized ZnS nanowire sensors showed responses of 168-313% to 1-5 ppm NO2 at 300 degrees C in the dark. These values are comparable or superior to most semiconductor oxide one-dimensional nanostructures-based sensors reported in the literature. Furthermore, Au-functionalized ZnS nanowire sensors showed far higher responses (291-884%) to 1-5 ppm NO2 at 300 degrees C under UV illumination. The NO2 gas sensing mechanism of the Au-functionalized ZnS nanowire sensors under UV illumination is discussed.
    Sensors and Actuators B Chemical 11/2013; 188:1270-1276. DOI:10.1016/j.snb.2013.07.076 · 3.84 Impact Factor
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    ABSTRACT: Branched ZnO nanowires were synthesized using a three-step process: 1) synthesis of ZnO nanowires by the thermal evaporation of a mixture of ZnO and graphite powders on Au-coated C-plane sapphire substrates for 1 h, 2) deposition of Au on the as-synthesized ZnO nanowires, and 3) resumption of the thermal evaporation process for 10 min. The multiple-networked branched ZnO nanowire sensors exhibited far superior NO2 gas sensing properties than the unbranched nanowires. The origin of the enhanced NO2 gas sensing properties is also discussed.
    Thin Solid Films 11/2013; DOI:10.1016/j.tsf.2013.02.021 · 1.87 Impact Factor
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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; 115(4):558-. DOI:10.1007/s00339-013-7964-0 · 1.69 Impact Factor
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    ABSTRACT: Al2O3/ZnO coaxial nanowires were synthesized on (1 0 0) Si substrates by the thermal evaporation of a mixture of Al and TiO2 powders followed by atomic layer deposition of ZnO. Scanning electron microscopy revealed the Al2O3/ZnO coaxial nanowires to have a meandering shape with diameters of a few hundreds of nanometers, lengths of a few tens of micrometers and a ZnO shell layer thicknesses of 8-11 nm. Transmission electron microscopy and X-ray diffraction indicated that the cores and shells of the coaxial nanowires were single crystal rhombohedral-structured alpha-Al2O3 and polycrystalline wurtzite-structured ZnO, respectively. Al, Zn and O were detected in the energy dispersive X-ray spectrum, indicating that the coaxial nanowires contained almost no contaminants. The photoluminescence measurements showed that the Al2O3 nanowires had two weak emission bands centered at similar to 710 nm in the red region similar to 340 nm in the near-ultraviolet region. In contrast, Al2O3/ZnO coaxial nanowires had two emission bands: an emission band centered at approximately 570 nm in the yellow region and a weak emission band at approximately 340 nm in the near-ultraviolet region. The yellow emission might have originated from the ZnO shells in the Al2O3/ZnO coaxial nanowires, whereas the weak near-ultraviolet emission might be from the Al2O3 cores in the core-shell nanowires. (c) 2013 Elsevier B.V. All rights reserved.
    Optical Materials 08/2013; 35(10):1824-1828. DOI:10.1016/j.optmat.2013.03.023 · 2.08 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. DOI:10.1016/j.ceramint.2012.12.026 · 2.09 Impact Factor
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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. DOI:10.1016/j.cap.2013.01.020 · 2.03 Impact Factor
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    ABSTRACT: This study examined the influence of ZnO coating and annealing on the photoluminescence properties of the Ga2S3 nanostructures. Scanning electron microscopy showed that the Ga2S3/ZnO core-shell nanostructures synthesized using a two-step process consisting of thermal evaporation of Ga metal and S powders and atomic layer-deposition of ZnO had larva-like morphologies. The larva-like Ga2S3 nanostructures synthesized at 700 degrees C showed strong orange emission. The emission might be due to the localized states associated with S interstitials, Ga vacancies, stacking defects and surface states. The emission peak of the GaS nanostructures was blue-shifted by ZnO coating. The ZnO shell layer thickness corresponding to the ALD cycle of 100 led to the highest emission intensity, which is more than three times higher than that of the uncoated Ga2S3 nanostructures. The emission intensity was further enhanced by annealing in a reducing atmosphere. The origins of the photoluminescence enhancements by ZnO coating and annealing are discussed.
    Current Applied Physics 07/2013; DOI:10.1016/j.cap.2012.12.017 · 2.03 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. DOI:10.1016/j.jpcs.2013.02.016 · 1.59 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 06/2013; 34(6). DOI:10.5012/bkcs.2013.34.6.1632 · 0.84 Impact Factor