Sang Sub Kim

Inha University, Sŏul, Seoul, South Korea

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Publications (141)239.91 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the switching behavior of as-deposited CrOx and post-annealed CrOy films by use of a variety of electrodes (top electrode Ag, Ti; bottom electrode Pt, fluorine tin oxide (FTO)). Resistance switching is highly dependent on electrode material and post-annealing treatment. Among Pt devices, I–V hysteresis was observed for the Ag/CrOx /Pt device only; no resistance switching was observed for Ag/CrOy /Pt, Ti/CrOx /Pt, and Ti/CrOy /Pt devices. Among FTO devices, I–V hysteresis was observed for the Ag/CrOx /FTO device whereas I–V hysteresis with the opposite switching direction was observed for Ag/CrOy /FTO, Ti/CrOx /FTO, and Ti/CrOy /FTO devices. The direction of switching depends not only on electrode material but also on post-annealing treatment, which affects the density of grain boundaries. Thus, the density of grain boundaries determines the type of charge carrier involved in the switching process. For as-deposited CrOx films with a high density of grain boundaries Ag filament paths mediated by electrochemical redox reaction were observed, irrespective of bottom electrode material (Pt or FTO). Post-annealed CrOy films with a low density of grain boundaries suppressed electrochemical redox reaction in the Ag/CrOy /Pt device but promoted short-range movement of O2− ions through the bottom interface, resulting in resistance switching in the Ag/CrOy /FTO device. Electrochemical redox reaction-controlled resistance switching occurred solely in oxides with a high density of grain boundaries or dislocations.
    Journal of Electronic Materials 07/2014; 43(7). · 1.64 Impact Factor
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    ABSTRACT: We report a dual functional sensing mechanism for ultrasensitive chemoresistive sensors based on SnO2-ZnO core-shell nanowires (C-S NWs) for detection of trace amounts of reducing gases. C-S NWs were synthesized by a two-step process, in which core SnO2 nanowires were first prepared by vapor-liquid-solid growth and ZnO shell layers were subsequently deposited by atomic layer deposition. The radial modulation of the electron-depleted shell layer was accomplished by controlling its thickness. The sensing capabilities of C-S NWs were investigated in terms of CO, which is a typical reducing gas. At an optimized shell thickness, C-S NWs showed the best CO-sensing capabilities, which were much superior to those of pure SnO2 nanowires without a shell. The dual functional sensing mechanism is proposed as the sensing mechanism in these nanowires, and is based on the combination of the radial modulation effect of the electron-depleted shell and the electric-field smearing effect.
    ACS Applied Materials & Interfaces 05/2014; · 5.01 Impact Factor
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    ABSTRACT: We have devised a sensor system comprising p-CuO/n-ZnO core-shell nanofibers (CS nanofibers) for the detection of reducing gases with a very low concentration. The CS nanofibers were prepared by a two-step process as follows: (1) synthesis of core CuO nanofibers by electrospinning, and (2) subsequent deposition of uniform ZnO shell layers by atomic layer deposition. We have estimated the sensing capabilities of CS nanofibers with respect to CO gas, revealing that the thickness of the shell layer needs to be optimized to obtain the best sensing properties. It is found that the p-CuO/n-ZnO CS structures are suitable for detecting reducing gases at extremely low concentrations. The associated sensing mechanism is proposed on the basis of the radial modulation of an electron-depleted region in the shell layer.
    Nanotechnology 04/2014; 25(17):175501. · 3.84 Impact Factor
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    ABSTRACT: Hydrothermally grown ZnO nanorods were used for enzyme immobilization in glucose sensors. In particular, the surface area of the ZnO nanorods was tailored by the use of a seed layer and/or by changing the concentration of the precursors. The glucose sensing capability was found to be strongly associated with the surface area of the nanorods. The results clearly demonstrated that hydrothermally grown ZnO nanorods be successfully applied to the electrode system for the detection of glucose. In addition, the growth conditions also need to be carefully optimized in order to grow ZnO nanorods that are as slim and long as possible in order to maximize the surface area.
    Sensors and Actuators B Chemical 01/2014; 192:216–220. · 3.54 Impact Factor
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    ABSTRACT: Ostwald ripening is an evolutionary mechanism that results in micro-scale carbon spheres from nano-scale spheres. Vapor-phase carbon elements from small carbon nanoparticles are transported to the surface of submicron-scale carbon spheres, eventually leading to their evolution to micro-scale spheres via well-known growth mechanisms, including the layer-by-layer, island, and mixed growth modes. The results obtained from this work will pave the way to the disclosure of the evolutionary mechanism of micro-scale carbon spheres and open a new avenue for practical applications.
    Scientific Reports 01/2014; 4:3579. · 2.93 Impact Factor
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    ABSTRACT: A new deep acceptor state is identified by density functional theory calculations, and physically activated by an Au ion implantation technique to overcome the high energy barriers. And an acceptor-compensated charge transport mechanism that controls the chemical sensing performance of Au-implanted SnO2 nanowires is established. Subsequently, an equation of electrical resistance is set up as a function of the thermal vibrations, structural defects (Au implantation), surface chemistry (1 ppm NO2), and solute concentration. We show that the electrical resistivity is affected predominantly not by the thermal vibrations, structural defects, or solid solution, but the surface chemistry, which is the source of the improved chemical sensing. The response and recovery time of chemical sensing is respectively interpreted from the transport behaviors of major and minor semiconductor carriers. This acceptor-compensated charge transport mechanism provides novel insights not only for sensor development but also for research in charge and chemical dynamics of nano-semiconductors.
    Scientific Reports 01/2014; 4:4622. · 2.93 Impact Factor
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    ABSTRACT: A novel one-pot synthesis method is used to prepare Au-loaded SnO2 nanofibers. The method combines the sol–gel and the electrospinning techniques in which the reduction process by ultraviolet exposure is included for in situ growth of Au nanoparticles in the electrospinning solution. Chemical gas sensors are fabricated by the use of the synthesized Au-loaded SnO2 nanofibers. According to the sensing measurements, the loading of Au significantly upgrades the sensing ability to CO in terms of response and selectivity. The optimization of content of Au nanoparticles incorporated in SnO2 nanofibers is likely to be a key parameter to maximize the sensing ability.
    Sensors and Actuators B Chemical 01/2014; 202:38–45. · 3.54 Impact Factor
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    ABSTRACT: We first report the mechanism of gas sensing improvement of reduced graphene oxides (RGOs) by electron-beam irradiation. We have irradiated the RGO samples by the electron beam with doses of 100 and 500 kGy. Raman spectra indicated that electron-beam irradiation generates defects. X-ray diffraction and X-ray photoelectron spectroscopy and initial resistance data consistently suggest that oxygen functional groups were increased by the electron-beam irradiation, with them being decreased by increasing the dose from 100 to 500 kGy. By the sensing test with respect to NO2 gas, we revealed that the NO2 response was increased not only by the electron-beam irradiation but also by increasing the electron dose. We revealed that the mechanism of the electron-beam-induced improvement of gas sensing behavior was dependent on the amount of electron dose. While the oxygen functional groups are likely to play a key role in enhancing the adsorption behavior of NO2 molecules in case of 100-kGy irradiation, further sensing enhancement at 500-kGy irradiation originates from the non-oxygen defects. The results suggest that the electron-beam irradiation can be a useful tool to turn the RGOs into more favorable sensing materials.
    Sensors and Actuators B Chemical 01/2014; 203:143–149. · 3.54 Impact Factor
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    ABSTRACT: Room temperature gas sensing ability for low concentrations of benzene was successfully realized with Pt nanoparticle-decorated networked ZnO nanowire sensors. For decoration of Pt nanoparticles, gamma-ray radiolysis was used. The Pt decoration greatly enhanced benzene sensing performances. Importantly, even at room temperature, ppm level benzene was clearly detected, which is likely to be due to the combined effect of electronic and chemical sensitizations by Pt nanoparticles.
    Journal of Nanoscience and Nanotechnology 10/2013; 13(10):7097-9. · 1.15 Impact Factor
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    ABSTRACT: We fabricated SnO2/Pt core-shell nanowires by means of a two-step process, in which Pt layers were sputtered onto the surface of networked SnO2 nanowires. For Pt-functionalization, we have synthesized the SnO2-Pt core-shell nanowires by depositing Pt layers using a sputtering method on bare SnO2 nanowires, subsequently annealing and thus transforming the continuous Pt shell layers into Pt nanoparticles. The NO2 gas sensing test demonstrated the ability of the Pt functionalization to attain the higher sensitivity and faster response than bare SnO2 nanowires. The possible mechanisms for improvment of the sensing properties by Pt-functionalization were discussed.
    Journal of Nanoscience and Nanotechnology 09/2013; 13(9):6216-21. · 1.15 Impact Factor
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    ABSTRACT: ZnO–SnO2 branch–stem nanostructures were realized on a basis of a two-step process. In step 1, SnO2-stem nanowires were synthesized. In step 2, ZnO-branch nanowires were successfully grown on the SnO2-stem nanowires through a simple evaporation technique. We have pre-deposited thin Au layers on the surface of SnO2 nanowire stems and subsequently evaporated Zn powders on the nanowires. The ZnO branches, which sprouted from the SnO2 stems, had diameters in a range of 30–35 nm. As-synthesized branches were of single crystalline hexagonal ZnO structures. Since the branch tips were comprised of Au-containing nanoparticles, the Au-catalyzed vapor–liquid–solid growth mechanism was more likely to control the growth process of the ZnO branches. To test a potential use of ZnO–SnO2 branch–stem nanostructures in chemical gas sensors, their sensing performances with respect to NO2 gas were investigated, showing the promising potential in chemical gas sensors.
    Current Applied Physics 05/2013; 13(3):526–532. · 1.81 Impact Factor
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    ABSTRACT: We have coated zinc-oxide (ZnO)-branched tin oxide (SnO2) nanowires with a Pd shell layer via a sputtering method and subsequently investigated the effects of thermal annealing. By the thermal annealing, the Pd shell layers were agglomerated to form the nanoparticles, being comprised of the cubic Pd phase. Sensing measurement in terms of NO2 gas revealed that the morphology of the Pd nanoparticles affected the sensing capability, in that the abundant and dense Pd nanoparticles obtained at certain temperatures enhanced the sensitivity to NO2 gas. We suggest that the spillover effect of Pd nanoparticles played a significant role in enhancing the response.
    Microelectronic Engineering 05/2013; 105:1–7. · 1.22 Impact Factor
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    ABSTRACT: Highly sensitive and selective NO2 sensing performances were realized with the networked SnO2 microrods functionalized with Ag nanoparticles by applying γ-ray radiolysis. The Ag nanoparticles were transformed into nanoparticles of the Ag/Ag2O phase by thermal heating. The NO2 sensing characteristics of the Ag-functionalized SnO2 microrods were compared with those of bare SnO2 microrods. The cross-sensibility of the Ag-functionalized SnO2 microrods to other gases was tested for O2, SO2, CO, C6H6 and C7H8. The sensing results demonstrated not only that γ-ray radiolysis was an effective means of functionalizing the surface of oxide microrods with catalytic Ag nanoparticles, but also that the Ag functionalization greatly enhanced the SnO2 microrods' capability of detecting NO2 in light of response and selectivity. The special energy band structure built on the surface of SnO2 microrods associated with Ag nanoparticles leads to a superior response to oxidizing gases than reducing gases. Being combined with this, easy dissociation of NO2 into more active chemical species by the unique catalytic role of Ag is likely to be responsible for the selective, sensitive NO2 sensing performances of the Ag-functionalized SnO2 microrods.
    J. Mater. Chem. C. 03/2013; 1(16):2834-2841.
  • Jae Young Park, Ju-Jin Kim, Sang Sub Kim
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    ABSTRACT: ZnO nanofibers were synthesized by the electrospinning method. Their electrical transport properties were investigated by fabricating field effect transistors based on single ZnO nanofiber. The electron concentration (n) and the field-effect mobility (μe) in the ZnO nanofibers are not so sensitive to the calcination atmosphere; O2 and N2. Importantly, n (μe) in the ZnO nanofibers is bigger (much smaller) than those in single-crystalline ZnO nanowires. The existence of nanosized gains in the ZnO nanofibers is likely to be responsible for such big differences in n and μe. Huge grain boundaries created by nanograins seem to play the role of a source providing electrons and a barrier for electrons to flow as well. To enhance the μe, the calcination condition to obtain ZnO nanofibers with larger grains needs to be applied.
    Microelectronic Engineering 01/2013; 101:8–11. · 1.22 Impact Factor
  • Eun-Kyeong Kim, Ji Yeong Kim, Sang Sub Kim
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    ABSTRACT: We describe the preparation of superhydrophobic SiO2 layers through a combination of surface roughness and fluorination. Electrospraying SiO2 precursor solutions that were prepared by a sol–gel route and included trichloro(1H,1H,2H,2H-perfluorooctyl)silane as a fluorination source produced highly rough, fluorinated SiO2 layers. In sharp contrast to the fluorinated flat SiO2 layer, the fluorinated rough SiO2 layer showed much enhanced repellency toward liquid droplets of different surface tensions. The surface fraction and the work of adhesion of the superhydrophobic SiO2 layers were determined, respectively, based on Cassie–Baxter and Young–Dupre equations. The satisfactory long-term stability for 30 days, the ultraviolet resistance and the thermal stability up to 400 oC of the superhydrophobic SiO2 layers prepared in this work confirm a promising practical application.
    Journal of Solid State Chemistry 01/2013; 197:23–28. · 2.04 Impact Factor
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    ABSTRACT: Amorphous SiO2 films were deposited by means of an electrospray technique. The relation between the water contact angle (WCA) of the deposited SiO2 films and the surface morphology is investigated. The feeding rate of the electrospray process greatly affects the morphology of the synthesized SiO2 films. There is also a significant change in the WCA on the surface of the films: the rougher the surface, the greater the WCA. A model based on the Cassie–Baxter formulation is used to explain the change observed in the WCA on the SiO2 films. Copyright © 2012 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 01/2013; 45(2). · 1.22 Impact Factor
  • So Yeon Jo, Ji Yeong Kim, Sang Sub Kim
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    ABSTRACT: In the present work, ZnO nanofibers were applied to electrode materials for the detection of cholesterol. ZnO nanofibers were synthesized using the electrospinning technique with zinc acetate as a precursor. Electrospinning-synthesized ZnO nanofibers were uniformly distributed by properly controlling the electrospinning parameters. After the calcination treatment, nanofibers of pure ZnO phase were synthesized. Then, these fibers were successfully placed on Au-coated glass substrates by dispersion of ZnO nanofibers in ethanol, dropping, and drying, in sequence. Cholesterol oxidase was then immobilized onto the surface of the ZnO nanofibers. To enhance the immobilization, Nafion was additionally applied. The sensing performances of the fabricated ZnO nanofibers-based sensors were analyzed by cyclic voltammetry in terms of cholesterol concentration ranging from 100 to 400 mg/dl. In the I-V curves, measured by cyclic voltammetry, the ZnO nanofiber-based sensor showed a proportional current behavior with cholesterol concentrations in phosphate buffered saline solution. The sensitivity was measured and found to be , which is comparable to the values reported in the literature. After not only optimizing the shape of the ZnO nanofibers but also improving the adhesion nature between the ZnO nanofibers and the Au conducting layer, these fibers can be a good candidate for electrode materials in devices used to detect low concentrations of cholesterol in blood.
    Korean Journal of Materials Research 01/2013; 23(5).
  • Ji Yeong Kim, Eun-Kyeong Kim, Sang Sub Kim
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    ABSTRACT: Superhydrophobic layers with a micro-nano hierarchical surface structure were prepared. layers deposited via an electrospray method combined with a sol-gel chemical route were rough on the microscale. Au particles were decorated on the surface of the microscale-rough layers by use of the photo-reduction process with different intensities () and illumination times (60-240 sec) of ultraviolet light. With the aid of nanoscale Au nanoparticles, this consequently resulted in a micro-nano hierarchical surface structure. Subsequent fluorination treatment with a solution containing trichloro(1H,2H,2H,2H-perfluorooctyl)silane fluorinated the hierarchical layers. The change in surface roughness factor was in good agreement with that observed for the water contact angle, where the surface roughness factor developed as a measure needed to evaluate the degree of surface roughness. The resulting layers revealed excellent repellency toward various liquid droplets with different surface tensions ranging from 46 to 72.3 mN/m. Especially, the micro-nano hierarchical surface created at an illumination intensity of and illumination time of 60 sec showed the largest water contact angle of . Based on the Cassie-Baxter and Young-Dupre equations, the surface fraction and work of adhesion for the micronano hierarchical layers were evaluated. The work of adhesion was estimated to be less than for all the liquid droplets. This exceptionally small work of adhesion is likely to be responsible for the strong repellency of the liquids to the micro-nano hierarchical layers.
    Korean Journal of Materials Research 01/2013; 23(1).
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    ABSTRACT: Networked SnO(2) nanowire sensors were achieved using the selective growth of SnO(2) nanowires and their tangling ability, particularly on on-chip V-groove structures, in an effort to overcome the disadvantages imposed on the conventional trench-structured SnO(2) nanowire sensors. The sensing performance of the V-groove-structured SnO(2) nanowire sensors was highly dependent on the geometrical dimension of the groove, being superior to those of their conventional trench-structured counterparts. Pt nanoparticles were decorated on the surface of the networked SnO(2) nanowires via γ-ray radiolysis to enhance the sensing performances of the V-groove sensors whose V-groove widths had been optimized. The V-groove-structured Pt-nanoparticle-decorated SnO(2) nanowire sensors exhibited outstanding and reliable sensing capabilities towards toluene and nitrogen dioxide gases, indicating their potential for use as a platform for chemical gas sensors.
    Nanotechnology 12/2012; 24(2):025504. · 3.84 Impact Factor
  • Ji-Yeong Kim, Eun-Kyeong Kim, Sang Sub Kim
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    ABSTRACT: This paper reports the preparation of superhydrophobic SiO(2) layers with a micro-nano hierarchical surface structure. SiO(2) layers, which were rough on the microscale, were prepared using an electrospraying method combined with a sol-gel chemical route. To create a nanoscale structure, the surface of the SiO(2) layers was coated with Au nanoparticles using an ultraviolet-enhanced chemical reduction process, resulting in a micro-nano hierarchical surface structure. A subsequent fluorination treatment with a solution containing trichloro(1H,1H,2H,2H-perfluorooctyl)silane resulted in fluorination of the micro-nano hierarchical SiO(2) layers. The resulting SiO(2) layers showed outstanding repellency toward a range of liquid droplets, for example, a water-repellency of 170°. The surface fraction and work of adhesion of the fluorinated, micro-nano hierarchical SiO(2) layers were estimated using the Cassie-Baxter and Young-Dupre equations, respectively. The long-term durability and ultraviolet resistance of the superhydrophobic SiO(2) layers prepared in this study highlight their potential in a range of practical applications.
    Journal of Colloid and Interface Science 10/2012; · 3.17 Impact Factor

Publication Stats

650 Citations
239.91 Total Impact Points

Institutions

  • 2007–2014
    • Inha University
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
  • 2013
    • Hanyang University
      • Division of Materials Science and Engineering (MSE)
      Sŏul, Seoul, South Korea
  • 2011
    • Kookmin University
      Sŏul, Seoul, South Korea
  • 2010
    • Inter University Accelerator Centre
      New Dilli, NCT, India
  • 2002–2007
    • Chonnam National University
      • Department of Material Science and Engineering
      Gwangju, Gwangju, South Korea
  • 2004
    • Korea Photonics Technology Institute
      Sŏul, Seoul, South Korea
  • 2003–2004
    • Pohang University of Science and Technology
      • Department of Materials Science and Engineering
      Andong, North Gyeongsang, South Korea
  • 1999–2002
    • Sunchon National University
      • Department of Materials Science and Metallurgical Engineering
      South Korea