Sang Sub Kim

Inha University, Sŏul, Seoul, South Korea

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Publications (152)294.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Networked ZnO nanowires were fabricated via a vapor-phase selective growth method. Pt nanoparticles were functionalized on the networked ZnO nanowires. In this study, for the functioanlization, γ-ray radiolysis was applied. By the method, Pt nanoparticles of ∼10 nm in diameter were uniformly anchored on the surface of each ZnO nanowire. The sensing properties of the Pt-functionalized, networked ZnO nanowires were investigated in terms of NO2, CO and benzene at 100 °C. The sensing capability of the Pt-functionalized ZnO nanowires at that temperature supports their potential use in chemical gas sensors.
    Journal of Nanoscience and Nanotechnology 01/2015; 15(1). · 1.15 Impact Factor
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    ABSTRACT: This paper proposes a method for improving the reducing or oxidizing gas-sensing abilities of p-type oxide nanowires (NWs) by locally modifying the hole-accumulation channel through the attachment of p-type nanoparticles (NPs) with different upper valence band levels. In this study, the sensing behaviors of p-CuO NWs functionalized with either p-NiO or p-Co3O4 NPs were investigated as a model materials system. The attachment of p-NiO NPs greatly improved the reducing gas-sensing performance of p-CuO NWs. In contrast, the p-Co3O4 NPs improved the oxidizing gas-sensing properties of p-CuO NWs. These results are associated with the local suppression/expansion of the hole-accumulation channel of p-CuO NWs along the radial direction due to hole flow between the NWs and NPs. The approach proposed in this study provides a guideline for fabricating sensitive chemical sensors based on p-CuO NWs.
    ACS Applied Materials & Interfaces 12/2014; · 5.90 Impact Factor
  • Akash Katoch, Jae-Hun Kim, Sang Sub Kim
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    ABSTRACT: TiO2/ZnO double-layer hollow fibers (DLHFs) are proposed as a superior sensor material in comparison to regular single-layer hollow fibers (HFs) for the detection of reducing gases. DLHFs were synthesized on sacrificial polymer fibers via atomic layer deposition of a first layer of TiO2 followed by a second layer of ZnO and by a final thermal treatment. The inner TiO2 receives electrons from the ZnO outer layer, which becomes more resistive due to the significant loss of electrons. This highly resistive ZnO layer partially regains its original resistivity when exposed to reducing gases such as CO, thus enabling more resistance variation in DLHFs. DLHFs are a novel material compared to HFs and can be successfully employed to fabricate chemical sensors for the accurate detection of reducing gases.
    ACS Applied Materials & Interfaces 11/2014; · 5.90 Impact Factor
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    ABSTRACT: A novel one-pot synthesis method for Pt-loaded SnO2 nanofibers is reported on the basis of the sol–gel and electrospinning-combined process. The ultraviolet illumination was used for in-situ growth of Pt nanoparticles in the electrospinning solution. The sensing capability of pure SnO2 nanofibers was significantly improved by loading Pt nanoparticles. The Pt-loaded SnO2 nanofibers showed a good selectivity to toluene gas. The optimization of Pt amount in SnO2 nanofibers was essential to obtain best sensing performances. The one-pot synthesis method developed in this work may extend the use of oxide nanofibers in chemical gas sensors.
    Journal of Nanoscience and Nanotechnology 11/2014; 14(11). · 1.15 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 11/2014; 203:143–149. · 3.84 Impact Factor
  • Akash Katoch, Sun-Woo Choi, Sang Sub Kim
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    ABSTRACT: ZnO hollow fibers (HFs) with a range of wall thicknesses were synthesized by electrospinning and atomic layer deposition. The effects of the wall thickness of the HFs on their sensing properties were examined using CO as a representative reducing gas. The thin-walled HFs showed improved sensor responses to CO compared to thick-walled HFs. Most importantly, despite the polycrystalline nature of HFs, their sensing abilities were determined mainly by the wall thickness, not by the size of the nanograins or crystalline quality. In particular, the resistance modulation was attributed mainly to radial suppression/broadening of the underlying conducting channel during adsorption/desorption of gas species on both the inner and outer surface.
    Nanotechnology 10/2014; 25(45):455504. · 3.84 Impact Factor
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    ABSTRACT: A novel approach to improving the reducing gas-sensing properties of n-type nanowires (NWs), by locally creating p-n heterojunctions with p-type nanoparticles (NPs), is proposed. As a model system, this work investigates the sensing behaviors of n-SnO2 NWs functionalized with p-Cr2O3 NPs. Herein, n-SnO2 NWs demonstrate greatly improved reducing gas-sensing performance when functionalized with p-Cr2O3 NPs. Conversely, such functionalization deteriorates the oxidizing gas-sensing properties of n-SnO2 NWs. These phenomena are closely related to the local suppression of the conduction channel of n-type NWs, in the radial direction, beneath the p-n heterojunction by the flow of charge carriers. The approach used in this work can be used to fabricate sensitive reducing-gas sensors based on n-type NWs.
    ACS Applied Materials & Interfaces 10/2014; · 5.90 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 10/2014; 202:38–45. · 3.84 Impact Factor
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    ABSTRACT: The attachment of n-TiO2 nanoparticles (NPs) onto networked p-CuO nanowires (NWs) greatly improves the sensing abilities of the NWs for oxidizing gases. However, the attachment is harmful to the detection of reducing gases. In contrast to the case of pristine p-CuO NWs in which the hole-accumulation layer is equally modulated in the radial direction in NWs during adsorption and desorption of oxidizing and reducing gases, the attachment of n-TiO2 NPs induces less modulation for reducing gases but more modulation for oxidizing gases. This is because a biased modulation of the hole-accumulation layer is established by the charge carrier transfer between NWs and NPs. The approach in this study provides an insight into designing p-type NW sensors for sensitive detection of oxidizing gases.
    J. Mater. Chem. C. 09/2014;
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    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; · 5.90 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: 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 04/2014; 4:4622. · 5.08 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 03/2014; 192:216–220. · 3.84 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. · 5.08 Impact Factor
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    ABSTRACT: Based on the radial modulation of electron-depleted shell layers in SnO2–ZnO core–shell nanofibers (CSNs), a novel approach is proposed for the detection of very low concentrations of reducing gases. In this work, SnO2–ZnO CSNs were synthesized by a two-step process: core SnO2 nanofibers were first prepared by electrospinning, followed by the preparation of ZnO shell layers by atomic layer deposition. The radial modulation of electron depletion in the CSN shells was accomplished by controlling the shell thickness. The sensing capabilities of CSNs were investigated with respect to CO and NO2 that represent typical reducing and oxidizing gases, respectively. In the case of CO at a critical shell thickness, the CSN-based sensors showed greatly improved sensing capabilities compared with those fabricated on the basis of either pure SnO2 or pure ZnO nanofibers. In sharp contrast, CSN sensors revealed inferior sensing capabilities for NO2. The results can be explained by a model based on the radial modulation of the electron-depleted CSN shells. The model suggests that CSNs comprising dissimilar materials having different energy-band structures represent an effective sensing platform for the detection of low concentrations of reducing gases when the shell thickness is equivalent to the Debye length.
    J. Mater. Chem. A. 10/2013; 1(43).
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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: In this study, a bi-functional mechanism is proposed and validated, which may be used to explain all of the reported experimental observations and to predict new sensing control parameters. Fast response and recovery in H2S sensing was then realized by using bi-functional SnO2 nanowires which have been radially modulated with CuO. Firstly, Cu metal nanoparticles were synthesized by applying γ-ray radiolysis. The Cu nanoparticles (attached to the surface of the SnO2 nanowires) were oxidized to the CuO phase by a thermal treatment at 500 °C in air. The H2S sensing characteristics of the CuO-functionalized SnO2 nanowires were compared with those of bare SnO2 nanowires. The results demonstrated that γ-ray radiolysis is an effective means of functionalizing the surface of oxide nanowires with CuO nanoparticles, and CuO functionalization greatly enhanced the ability of the SnO2 nanowires to detect H2S in terms of the response and recovery times. In addition, two control parameters, a 0.5 CuO to SnO2 surface ratio and a sensing temperature range of 80–220 °C, are predicted. The radially modulated nanostructures achieve two functions: (1) the formation and break-away of p–n (CuO–SnO2) junctions, and (2) the formation and dissolution of CuS using CuO–SnO2 solid solutions.
    J. Mater. Chem. C. 08/2013; 1(35).
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    ABSTRACT: Bimetallic Pd/Pt nanoparticles were used to functionalize networked SnO2 nanowires in order to realize a fast response and recovery ability in their NO2-sensing performance. Pd and Pt nanoparticles with diameters of 10–40 nm were uniformly decorated on networked SnO2 nanowires via a sequential γ-ray radiolysis. The NO2-sensing performance in terms of response and recovery times of the bimetallic Pd/Pt-functionalized SnO2 nanowire sensor was compared to the ones based on bare SnO2 nanowires, or functionalized by either Pd or Pt nanoparticles, respectively. The bimetallic functionalized SnO2 nanowire sensor revealed faster response (13 s) and recovery (9 s) times due to the synergic effect of individual Pd and Pt nanoparticles. The results indicate that the approach of a functionalization by bimetallic nanoparticles has a promising potential to enhance the sensing performances of oxide nanowires.
    Sensors and Actuators B Chemical 05/2013; 181:446–453. · 3.84 Impact Factor

Publication Stats

766 Citations
294.96 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
  • 1999–2004
    • Sunchon National University
      • Department of Materials Science and Metallurgical Engineering
      Junten, South Jeolla, South Korea