Sang Sub Kim

Inha University, Chemulpo, Incheon, South Korea

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Publications (183)447.53 Total impact

  • Zain Ul Abideen · Hyoun Woo Kim · Sang Sub Kim
    Chemical Communications 08/2015; DOI:10.1039/C5CC05370F · 6.83 Impact Factor
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    ABSTRACT: We have fabricated sensors with reduced graphene oxide (RGO) nanosheets (NSs)-loaded ZnO nanofibers (NFs) via an electrospinning method. The RGO NSs-loaded ZnO NFs were comprised of nanograins with an average diameter of 20 nm. Transmission electron microscopy and X-ray diffraction both revealed the presence of RGO NSs in the ZnO NFs. The sensing properties of RGO NSs-loaded ZnO NFs were examined after exposure to various gases, including O2, SO2, NO2, CO, C6H6, and C2H5OH. The sensor responses showed a bell-shaped behavior with respect to the weight ratio of RGO NSs. It is remarkable that our sensors exhibited significantly higher responses than pure ZnO NFs. We propose a novel hybrid sensing mechanism for the drastic improvement in the sensing behavior that is caused by loading RGO NSs into ZnO NFs. This hybrid sensing mechanism combines the resistance modulation of ZnO/ZnO homointerfaces and RGO-NSs/ZnO heterointerfaces in addition to the radial modulation of the surface depletion layer of ZnO NFs. In the heterointerfaces, the creation of local heterojunctions plays a significant role in raising the sensitivity of RGO-loaded ZnO NFs.
    Sensors and Actuators B Chemical 08/2015; DOI:10.1016/j.snb.2015.07.120 · 4.29 Impact Factor
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    ABSTRACT: The evolution of low symmetric phases was investigated in epitaxial (Ba0.5, Sr0.5)TiO3 (BST) thin films grown on Si with yttria stabilized zirconia (YSZ). Paraelectric cubic BST thin films, when exposed to tensile strain primarily due to Si, present low symmetric phases, tetragonal c and monoclinic r phases, depending on the thickness of the BST thin films. When BST films are thin (80 nm), BST thin layers are in a mixed state of r and c phases. As the thickness of the BST layers further increases, the c phase rapidly disappears, and the monoclinic r phase becomes predominant. These strained BST thin films exhibit non-zero polarization and manifest themselves by non-volatility in a metal-ferroelectric-insulator structure on Si, which is attributed to the non-cubic phases developed by strained BST thin films.
    Science of Advanced Materials 08/2015; 7(8). DOI:10.1166/sam.2015.2366 · 2.91 Impact Factor
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    ABSTRACT: ZnO–CuO composite nanofibers were used for the detection of H2S. Various nanograin sizes were obtained by changing the heat treatment duration. The nanograin size greatly influenced the H2S-sensing performance of the resulting composites. Composite nanofibers consisting of smaller nanograins showed superior sensing properties compared to the composite nanofibers of larger ones. The mechanism is based on the known transition process from the p-CuO-n-ZnO junction to the metallic-CuS-n-ZnO junction in the presence of H2S. This study suggests that the nanograin size needs to be as small as possible to obtain the maximum H2S-sensing properties in CuO-n-type oxide (ZnO or SnO2) composite nanofibers by controlling the heat treatment condition, such as the duration and temperature.
    Sensors and Actuators B Chemical 07/2015; 214. DOI:10.1016/j.snb.2015.03.012 · 4.29 Impact Factor
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    Jae-Hun Kim · Akash Katoch · Soo-Hyun Kim · Sang Sub Kim
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    Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: In this paper, we report the exceptional toluene-sensing properties of SnO2-ZnO core-shell nanowires (C-S NWs) functionalized with Pt nanoparticles (NPs). A response of 279 was obtained for 100 ppb of toluene, and to the best of our knowledge, this is the highest toluene response to be reported in the literature. The SnO2-ZnO C-S NWs were synthesized via a two-step process: first, a networked core of SnO2 nanowires was prepared via vapor-liquid-solid growth on the patterned electrode layer. Second, the ZnO shell layers were created with atomic layer deposition. The electron-depleted region of the shell layer was further expanded by attaching Pt NPs, which were synthesized using g-ray radiolysis, to the shell layer. In addition to the expansion of the electron-depleted region, the catalytic effect of Pt on toluene greatly improved the toluene-sensing performance of the C-S NWs. The extraordinary toluene-sensing ability of the Pt-functionalized C-S NWs means they have great potential as the sensing platform in exhaled breath sensors used to diagnose lung cancer.
    ACS Applied Materials & Interfaces 07/2015; DOI:10.1021/acsami.5b04066 · 6.72 Impact Factor
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    Jae-Hun Kim · Akash Katoch · Sun-Woo Choi · Sang Sub Kim
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    ABSTRACT: Networked p-CuO nanowires were grown on patterned-electrode pads by the thermal oxidation of Cu layers. Vertically aligned CuO nanowires grown on adjacent round-shape electrode pads were entangled, eventually forming nanowire–nanowire junctions. The sensing properties of the networked CuO nanowires were examined for a range of oxidizing gases, such as NO2, SO2 and O2, and reducing gases, such as CO, C6H6, C7H8, and H2, and compared with those of networked n-SnO2 nanowires. The gas responses of the networked CuO nanowires to the tested oxidizing gases were inferior to those of networked n-SnO2 nanowires. In contrast, for reducing gases, the networked CuO nanowires showed comparable gas responses to the networked n-SnO2 nanowires. The results suggest that the networked CuO nanowires are more promising for the detection of reducing gases rather than oxidizing gases.
    Sensors and Actuators B Chemical 06/2015; 212. DOI:10.1016/j.snb.2014.12.081 · 4.29 Impact Factor
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    Jae-Hun Kim · Akash Katoch · Soo-Hyun Kim · Sang Sub Kim
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    ABSTRACT: We report the synthesis of SnO2?Cu2O n?p core?shell nanowires (C?S NWs) and their use as chemiresistive sensors for detecting trace amounts of gas. The n?p C?S NWs were synthesized by a two-step process, in which the core SnO2 nanowires were prepared by the vapor growth technique and subsequently the Cu2O shell layers were deposited by atomic layer deposition. A systematic investigation of the sensing capabilities of the n?p C?S NWs, particularly as a function of shell thickness, revealed the underlying sensing mechanism. The radial modulation of the hole-accumulation layer is intensified under shells thinner than the Debye length. On the other hand, the contribution of volume fraction to resistance modulation is weakened. By the combination of these two effects, an optimal sensing performance for reducing gases is obtained for a critical p-shell thickness. In contrast, the formation of p-shell layers deteriorates the NO2-sensing performance by blocking the expansion of the hole-accumulation layer due to the presence of p?n heterointerface.
    ACS Applied Materials & Interfaces 06/2015; DOI:10.1021/acsami.5b03224 · 6.72 Impact Factor
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    ABSTRACT: Bandgap engineering of atomically thin 2D crystals is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here, we report a simple but rather unexpected approach for bandgap engineering of muscovite-type mica nanosheets (KAl3Si3O10(OH)2) via controlled molecular thickness. Through density functional calculations, we analyze electronic structures in 2D mica nanosheets and develop a general picture for tunable bandgap narrowing induced by controlled molecular thickness. From conducting atomic force microscopy, we observe an abnormal bandgap narrowing in 2D mica nanosheets, contrary to well-known quantum size effects. In mica nanosheets, decreasing the number of layers results in reduced bandgap energy from 7 to 2.5 eV, and the bilayer case exhibits a semiconducting nature with ∼2.5 eV. Structural modeling by transmission electron microscopy and density functional calculations reveal that this bandgap narrowing can be defined as a consequence of lattice relaxations as well as surface doping effects. These bandgap engineered 2D mica nanosheets open up an exciting opportunity for new physical properties in 2D materials and may find diverse applications in 2D electronic/optoelectronic devices.
    Chemistry of Materials 06/2015; 27(12):150610090301009. DOI:10.1021/cm504802j · 8.54 Impact Factor
  • Sang Sub Kim · Han Gil Na · Hyoun Woo Kim · Vadym Kulish · Ping Wu
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    ABSTRACT: We have realized a p-type-like conduction in initially n-type SnO2 nanowires grown using a vapor-liquid-solid method. The transition was achieved by irradiating n-type SnO2 nanowires with a high-energy electron beam, without intentional chemical doping. The nanowires were irradiated at doses of 50 and 150 kGy, and were then used to fabricate NO2 gas sensors, which exhibited n-type and p-type conductivities, respectively. The tuneability of the conduction behavior is assumed to be governed by the formation of tin vacancies (under high-energy electron beam irradiation), because it is the only possible acceptor, excluding all possible defects via density functional theory (DFT) calculations. The effect of external electric fields on the defect stability was studied using DFT calculations. The measured NO2 sensing dynamics, including response and recovery times, were well represented by the electron-hole compensation mechanism from standard electron-hole gas equilibrium statistics. This study elucidates the charge-transport characteristics of bipolar semiconductors that underlie surface chemical reactions. The principles derived will guide the development of future SnO2-based electronic and electrochemical devices.
    Scientific Reports 06/2015; 5:10723. DOI:10.1038/srep10723 · 5.58 Impact Factor
  • Zain Ul Abideen · Sang Sub Kim
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    ABSTRACT: In this study, n-ZnO nanofibers (NFs) were electronically sensitized by optimal loading of reduced graphene oxide nanosheets (RGO NSs). The RGO NSs-loaded ZnO NFs were comprised of nanograins with an average diameter of 20 nm. The sensing characteristics of RGO NSs-loaded ZnO NFs were examined with respect to various oxidizing and reducing gases, (O2, SO2, NO2, CO, C6H6, and C2H5OH). The sensor responses exhibited a bell-shaped behavior as a function of the weight ratio of RGO NSs. It is remarkable that gas-sensing characteristics were significantly improved and responses were higher than pure n-ZnO NFs. We propose a novel hybrid sensing mechanism for the drastic improvement of sensing behavior by loading RGO NSs into n-ZnO NFs. This hybrid sensing mechanism combines the resistance modulation of both the ZnO-ZnO homointerfaces and that of p-RGO NSs-n-ZnO heterointerfaces in addition to the radial modulation of the surface depletion layer of ZnO NFs.
    The spring meeting of Materials Research Society of Korea, GumiCo (Gumi Convention and Exhibition Center); 05/2015
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    ABSTRACT: SnO2-ZnO composite nanofibers fabricated using an electrospinning method exhibited exceptional hydrogen (H2) sensing behavior. The existence of tetragonal SnO2 and hexagonal ZnO nanograins was confirmed by an analysis of the crystalline phase of the composite nanofibers. A bifunctional sensing mechanism of the composite nanofibers was proposed in which the combined effects of SnO2-SnO2 homointerfaces and ZnO-SnO2 heterointerfaces contributed to an improvement in the H2 sensing characteristics. The sensing process with respect to SnO2-ZnO heterojunctions is associated not only with the high barrier at the junctions, but also the semiconductor-to-metallic transition on the surface of the ZnO nanograins upon the introduction of H2 gas.
    ACS Applied Materials & Interfaces 05/2015; 7(21). DOI:10.1021/acsami.5b01817 · 6.72 Impact Factor
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    ABSTRACT: In this paper we investigate O2 sensing dynamics in BiFeO3 (BFO) nanofibers at various concentrations and temperatures, by using a combined experiment and computer simulation approach. Samples of pristine BFO, Ni-doped BFO, and Pb-doped BFO nanofibers were prepared. By incorporating Ni and Pb, additional acceptor states are introduced in BFO. Density functional theory calculations show that Ni prefers to substitute Fe site while Pb substitutes Bi site, resulting in a new deep donor originating from Ni interstitial defects, along with oxygen vacancies (Vo). We find that both the sensing response and recovery time are shorter in samples made of pristine BFO nanofibers than in Ni- and Pb-doped nanofiber samples. We interpret the observed sensing dynamics through charge transport theory of the major (acceptors) and minor (donors) carriers, and found that the minor carrier compensation plays a significant role in determining the response and recovery time of the sensor device. This minor carrier compensation charge transport mechanism will provide new insights into more robust sensor development strategies, and into the research of ion-electron coupling in chemical dynamics of semiconductors.
    Nanotechnology 05/2015; 26(17):175501. DOI:10.1088/0957-4484/26/17/175501 · 3.67 Impact Factor
  • Akash Katoch · Sun-Woo Choi · Hyoun Woo Kim · Sang Sub Kim
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    ABSTRACT: We report, and propose a mechanism for, the exceptional hydrogen gas (H2) sensing ability of ZnO nanofibers. In comparison to SnO2 nanofibers, ZnO nanofibers show outstanding H2 gas response and unmistakable H2 selectivity. Different from the reducing gas effect observed in SnO2 nanofibers, a semiconductor-to-metal transition that occurs in the presence of H2 gas molecules is responsible for the exceptional response and selectivity of ZnO nanofibers to H2. Notably, the presence of nanograins within nanofibers further intensifies the resistance modulation observed due to this transition.
    Journal of Hazardous Materials 04/2015; 286. DOI:10.1016/j.jhazmat.2014.12.007 · 4.33 Impact Factor
  • Akash Katoch · Sun-Woo Choi · Sang Sub Kim
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    ABSTRACT: Oxide nanofibers synthesized by the electrospinning method have received considerable attention owing to their potential applications in various fields. This paper provides an overview of the growth behavior and the importance of the presence of nanograins in oxide nanofibers synthesized by the electrospinning method. The growth behavior of nanograins in various oxide nanofibers is described in terms of its effect on activation energy and growth exponent, which are then compared with the bulk counterparts. The lower activation energy of nanograins in nanofibers by an order of magnitude revealed that the active participation of nanograins during grain growth is due to higher chemical potential of atoms presented in nanosized grains. In addition, the influences of nanograins on the electrical, gas-sensing, magnetic, optical, and photocatalytic properties of nanofibers are discussed. It is shown that optimization of the nanograin size is essential to ensure that the advantages of oxide nanofibers are utilized in different applications.
    Metals and Materials International 03/2015; 21(2):213-221. DOI:10.1007/s12540-015-4319-8 · 1.22 Impact Factor
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    ABSTRACT: The sensing properties of Sb2O5 nanowires are reported for the first time. By varying the heating temperature of a mixture of Sb and Bi powders, we have successfully prepared Sb2O5 nanowires. For nanowires grown at 600°C, the stem is mainly comprised of a monoclinic Sb2O5 phase, with a trace amount of a monoclinic Bi2O3 phase. The existence of Au nanoparticles at the tips suggests that the 600°C-synthesized nanowires are mainly grown via a vapor-liquid-solid process. The 500°C-grown products comprise a small amount of 1D nanostructures, whereas the 700°C-grown product does not exhibit sufficiently thin 1D nanostructures. A representative A survey XPS spectrum exhibits several peaks, including Sb 3p, Sb 3d, O 1s, C 1s, Bi 4f, and Sb 4d. At room temeperature, the sensor response, response time, and recovery time of the nanowires were measured to be 1.20, 2104 s, and 6579 s, respectively. Sensor measurements employing NO2 gas indicate that the Sb2O5 nanowires synthesized in this work have potential for use as a room-temperature NO2 chemical gas sensors.
    Metals and Materials International 03/2015; 21(2):415-421. DOI:10.1007/s12540-015-4264-6 · 1.22 Impact Factor
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    ABSTRACT: We propose a novel approach to improve the gas-sensing properties of n-type nanofibers (NFs) that involves creation of local p-n heterojunctions with p-type reduced graphene oxide (RGO) nanosheets (NSs). This work investigates the sensing behaviors of n-SnO2 NFs loaded with p-RGO NSs as a model system. n-SnO2 NFs demonstrated greatly improved gas-sensing performances when loaded with an optimized amount of p-RGO NSs. Loading an optimized amount of RGOs resulted in a 20-fold higher sensor response than that of pristine SnO2 NFs. The sensing mechanism of monolithic SnO2 NFs is based on the joint effects of modulation of the potential barrier at nanograin boundaries and radial modulation of the electron-depletion layer. In addition to the sensing mechanisms described above, enhanced sensing was obtained for p-RGO NS-loaded SnO2 NFs due to creation of local p-n heterojunctions, which not only provided a potential barrier, but also functioned as a local electron absorption reservoir. These mechanisms markedly increased the resistance of SnO2 NFs, and were the origin of intensified resistance modulation during interaction of analyte gases with pre-adsorbed oxygen species or with the surfaces and grain boundaries of NFs. The approach used in this work can be used to fabricate sensitive gas sensors based on n-type NFs.
    ACS Applied Materials & Interfaces 01/2015; 7(5). DOI:10.1021/am5071656 · 6.72 Impact Factor
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    Sun-Woo Choi · Akash Katoch · Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: A novel approach to selectively improving the reducing or oxidizing gas-sensing abilities of n-type oxide nanowires (NWs), by modifying the conduction channel by the attachment of n-type nanoparticles (NPs) with different work functions, is proposed. Specifically, this work investigates the sensing behaviors of n-SnO2 NWs functionalized with either n-WO3 or n-TiO2 NPs. The greatly improved reducing gas-sensing performance of n-SnO2 NWs when functionalized with n-WO3 NPs is demonstrated. On the other hand, n-TiO2 NPs improve the oxidizing gas-sensing properties of n-SnO2 NWs. These phenomena are closely associated with the electron flow caused by the work function difference between the NWs and NPs, leading to either compression or expansion of the conduction channel of n-SnO2 NWs along the radial direction. This intensifies the resistance modulation of n-SnO2 NWs selectively to either reducing or oxidizing gases, respectively. The approach proposed in this study may contribute significantly to the realization of more sensitive NW sensors.
    01/2015; 3(7). DOI:10.1039/C4TC02057J
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    Akash Katoch · Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: CuO-SnO2 composite nanofibers with various nanograin sizes were synthesized for investigating their sensing properties with respect to H2S gas. The nanograin size in the CuO-SnO2 composite nanofibers was controlled by changing the thermal treatment duration under isothermal conditions. The nanograin size was found to be critical for the sensing ability of the composite nanofibers. The CuO-SnO2 composite nanofibers comprised of small-sized nanograins were more sensitive to H2S than those with larger-sized nanograins. The superior sensing properties of the CuO-SnO2 composite nanofibers with the smaller nanograins were attributed to the formation of the larger number of p-CuO-n-SnO2 junctions and their transformation to metallic-CuS-n-SnO2 contacts upon exposure to H2S gas. The results suggest that smaller nanograins are conducive to obtaining superior H2S-sensing properties in CuO-SnO2 composite nanofibers.
    Journal of Sensors 01/2015; 2015:1-7. DOI:10.1155/2015/387641
  • Akash Katoch · Sun-Woo Choi · Gun-Joo Sun · Sang Sub Kim
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    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). DOI:10.1166/jnn.2015.8368 · 1.34 Impact Factor

Publication Stats

2k Citations
447.53 Total Impact Points

Institutions

  • 2007–2015
    • Inha University
      • Department of Materials Science and Engineering
      Chemulpo, Incheon, South Korea
  • 2002–2007
    • Chonnam National University
      • Department of Material Science and Engineering
      Gwangju, Gwangju, South Korea
  • 1999–2002
    • Sunchon National University
      • Department of Materials Science and Metallurgical Engineering
      South Korea