Sang Sub Kim

Inha University, Incheon, Incheon, South Korea

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Publications (199)504.96 Total impact

  • Jes-Hun Kim · Akash Katoch · Hyoun Woo Kim · Sang Sub Kim
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    ABSTRACT: We have realized a highly sensitive, selective ppm-level carbon monoxide (CO) detection on the basis of graphene oxide (RGO) nanosheets-loaded SnO2 nanofibers with a simultaneous Au functionalization. The interplay between RGO/Au and SnO2 in terms of transferrence of charge carrier and modulation of potential barriers is responsible for the exceptionally high CO detectability.
    No preview · Article · Feb 2016 · Chemical Communications
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    ABSTRACT: We investigated the effect of grain size on the H2-sensing behavior of SnO2-ZnO composite nanofibers. The 0.9SnO2-0.1ZnO composite nanofibers were calcined at 700°C for various times to control the size of nanograins. A bi-functional sensing mechanism, which is related not only to the SnO2-SnO2 nanograins, but also to the ZnO-SnO2 nanograins with surface metallization effect, is responsible for the grain-oriented H2-sensing properties and the selective improvement in sensing behavior to H2 gas compared to other gases. Smaller grains are much more favorable for superior H2 sensing in SnO2-ZnO composite nanofibers, which will be an important guideline for their use in H2 sensors. The one-dimensional nanofiber-based structures in the present study will be efficient in maximizing the sensing capabilities by providing a larger amount of junctions.
    Full-text · Article · Jan 2016 · ACS Applied Materials & Interfaces
  • J.-H. Kim · Akash Katoch · Sang Sub Kim
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    ABSTRACT: We report on the sensing properties of p-n CuO-ZnO core-shell nanowires (C-S NWs) for reducing gases. The C-S NWs were synthesized by a two-step process: first, core p-CuO nanowires were prepared by thermal oxidation on patterned interdigital electrodes, forming a network; and second, the n-ZnO shell layers were subsequently deposited by atomic layer deposition (ALD). The ZnO shell thickness was controlled by changing the number of ALD cycles between 5 and 110 nm. The sensing properties of the C-S NWs were investigated for the typical reducing gases CO and C6H6. At 35 nm shell thickness, the C-S NWs showed the highest CO and C6H6 sensing ability, superior to that of pristine p-CuO nanowires. The sensing mechanism of the p-n C-S NWs is based on the radial modulation of an electron-depletion region in the ZnO shell layer, which occurs during the interaction between the reducing gas molecules and the adsorbed oxygen species and causes a pronounced change in resistance. This demonstrates that the radial modulation of the conducting channel is a universal sensing principle operating in p-n type C-S structures.
    No preview · Article · Jan 2016 · Sensors and Actuators B Chemical
  • Jong-Myoung Choi · Joon-Hyuk Byun · Sang Sub Kim
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    ABSTRACT: In this work, we confirmed the negligible influence of grain size on the gas-sensing capabilities of p-type semiconducting chemiresistive oxide gas sensors. For this purpose, p-type NiO nanofibers were synthesized by the electrospinning technique, and their sensing properties were investigated in terms of CO and NO2 (representative reducing and oxidizing gases, respectively) response, particularly as a function of the size of the nanograins existing in individual nanofibers. The size of the nanograins influenced the CO and NO2 response of the NiO nanofibers to only a small extent, in sharp contrast to its prominent influence on the sensor response of n-type semiconducting chemiresistive oxide gas sensors. The results not only confirm the established knowledge, but also provide a useful guideline for the fabrication of p-type oxide nanofiber-based chemical sensors.
    No preview · Article · Dec 2015 · Sensors and Actuators B Chemical
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    ABSTRACT: We demonstrated the preparation of high-performance toluene (C7H8) gas sensor, by using the Pt-multiwalled carbon nanotubes (MWCNTs) composite materials. We optimized the size of the Pt nanoparticles by controlling the predeposited Pt thickness, for obtaining the highest sensing performances. We have obtained the sensor responses of 3.91 and 5.06, at concentrations of 1 and 5 ppm of C7H8 gas, respectively, at 150 °C. We discussed the associated sensing mechanisms and proposed the reasons why the Pt-functionalization drastically enhanced the sensing behaviors of the Pt-MWCNTs composite sensors selectively to C7H8 gas.
    No preview · Article · Dec 2015 · Sensors and Actuators B Chemical
  • Jun-Seong Lee · Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: In this work, a possible mechanism for grain evolution in Al-Mg alloy films during thermal annealing is suggested on the basis of the phase transition and the related residual stress. Al-Mg alloy films with compositions of 14.0 and 18.0 wt.% Mg content were deposited on cold-rolled steel substrates by the direct current co-sputtering method using Al and Mg targets. After the deposition, the samples were thermally annealed at 400 degrees C for 10 min. The featureless, dense cross-sectional microstructure of the as-deposited films turned into a grainy microstructure after the thermal annealing. According to the residual stress evaluated by using the X-ray diffraction (XRD)-sin(2)psi technique and the phase analysis by XRD, it is likely that grains were created in order to relieve the additional accumulation of residual stress originating from the phase transition from face-centered cubic Al (alpha) to Al3Mg2 (beta) and Mg (delta) phases, suggesting an interplay between the microstructure and residual stress.
    No preview · Article · Nov 2015 · Thin Solid Films
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    Akash Katoch · Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: In this work we report the synthesis of copper oxide/tin oxide (CuO/SnO2) mixed nanofibers and their gas sensing properties in terms of H2S gas. The CuO/SnO2 mixed nanofibers were synthesized by electrospinning technique using two needles. Based on the thermogravimetric-differential thermal analysis, the calcination temperature was optimized at 700 °C to acquire both phases of CuO and SnO2. With this method, intermixed nanofibers of SnO2 and CuO were obtained. The sensing properties of the CuO/SnO2 mixed nanofibers to H2S are investigated as functions of operating temperature and gas concentration. The CuO/SnO2 mixed nanofibers were highly sensitive towards H2S with a response 522 for 10 ppm H2S and a response time 1 s at 300 °C. The semiconductormetal transition of CuO due to H2S is likely to the reason of the high H2S response. The results evidently demonstrate that the CuO/SnO2 mixed nanofibers synthesized with double needles are a promising sensor material for detection of H2S.
    Full-text · Article · Nov 2015 · Journal of Nanoscience and Nanotechnology
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    Zain Ul Abideen · Hyoun Woo Kim · Sang Sub Kim

    Full-text · Dataset · Oct 2015
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    ABSTRACT: In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiN X dielectrics. A negative gate bias temperature instability (NBTI) stress was applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (V th). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNX /SiO2 dielectric interface being dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the V th switches to the negative voltage direction, which is “turn-around” behavior. In the second stage, the V th moves from −1.63 V to −2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps.
    No preview · Article · Oct 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: In this study, we prepared solution-based In–Ga–ZnO thin film transistors (IGZO TFTs) having a multistacked active layer. The solution was prepared using an In:Zn = 1:1 mole ratio with variation in Ga content, and the TFTs were fabricated by stacking layers from the prepared solutions. After we measured the mobility of each stacked layer, the saturation mobility showed values of 0.8, 0.6 and 0.4 (cm2/Vs), with an overall decrease in electrical properties. The interface formed between the each layers affected the current path, resulting in reduced electrical performance. However, when the gate bias V G = 10 V was applied for 1500 s, the threshold voltage shift decreased in the stack. The uniformity of the active layer was improved in the stacked active layer by filling the hole formed during pre-baking, resulting in improved device stability. Also, the indium ratio was increased to enhance the mobility from 0.86 to 3.47. These results suggest high mobility and high stability devices can be produced with multistacked active layers.
    No preview · Article · Oct 2015 · Journal of Nanoscience and Nanotechnology
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    Zain Ul Abideen · Hyoun Woo Kim · Sang Sub Kim

    Full-text · Dataset · Sep 2015
  • 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.
    No preview · Article · Sep 2015 · Journal of Nanoscience and Nanotechnology
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    Zain Ul Abideen · Hyoun Woo Kim · Sang Sub Kim
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    ABSTRACT: We developed a hydrogen sensor of reduced graphene oxide-loaded ZnO nanofibers. An extremely high response of about 866 at a low concentration of 100 ppb was obtained. The combined effect of the presence of rGO nanosheets and hydrogen-induced metallization of ZnO played a crucial role in enhancing the detection behavior.
    Full-text · Article · Aug 2015 · Chemical Communications
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    Zain Ul Abideen · Hyoun Woo Kim · Sang Sub Kim
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    ABSTRACT: We developed a hydrogen sensor of reduced graphene oxide-loaded ZnO nanofibers. An extremely high response of about 866 at a low concentration of 100 ppb was obtained. The combined effect of the presence of rGO nanosheets and hydrogen-induced metallization of ZnO played a crucial role in enhancing the detection behavior.
    Full-text · Article · Aug 2015 · Chemical Communications
  • Yong Jung Kwon · Han Gil Na · Sang Sub Kim · Ping Wu · Hyoun Woo Kim
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    ABSTRACT: We report the growth of MgO nanowires surrounded by a donut-shaped spinel in a periodic way at a particular growth temperature of 1,000 °C. We examined the samples by means of scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction. At a lower temperature 950 °C, regular MgO nanowires grow. In contrast, at a higher temperature of 1,050 °C, spinel of (Mg0.4Al0.6)Al1.8O4 nanowires grow. From the absence of tip nanoparticles, we suggest that the synthesis of nanowires in the present study is dominated by a base-growth process. Based on the thermochemistry calculations, we propose that the absence of spinel in samples equilibrated at 950 °C is due to the catalytic-like behaviors of the silicon substrate which promotes the formation of MgO. In terms of choosing appropriate source materials, the technique reported here can be extended and exploited to produce various combinations of nanowire backbone structure with a surrounded nano-scale disk. © 2015, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.
    No preview · Article · Aug 2015 · Metals and Materials International
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    ABSTRACT: Hexagonal-boron nitride (h-BN) fullerenes were synthesized from a graphene oxide (GO) template by simultaneously heating the GO and B2O3 in the presence of NH3 gas. Transmission electron microscopy (TEM) observations revealed that a considerable amount of product had a fullerene-like nanostructure. Typical BN fullerenes have a polyhedral shape, being hollow nanocages. Lattice-resolved TEM and X-ray diffraction consistently demonstrated the formation of h-BN fullerenes. The FTIR spectrum exhibited absorption bands at approximately 800 and 1378 cm-1, which were related to the h-BN structure. The Raman spectra exhibited peaks at 1368 and 1399 cm-1, which can be related to BN sheets and BN fullerenes, respectively. The photoluminescence spectrum of the h-BN fullerenes taken at 8 K exhibited intense white-light emission. To reveal the origin of the broad emission band, which could be a superimposition of several peaks, we used a deconvolution procedure based on Gaussian functions. We proposed a growth mechanism of the h-BN fullerenes and verified it with a thermodynamic calculation. This work provides a cost-effective approach to synthesize fullerene-type boron nitride on a production scale. © 2015, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.
    No preview · Article · Aug 2015 · Metals and Materials International
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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.
    Full-text · Article · Aug 2015 · Sensors and Actuators B Chemical
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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.
    No preview · Article · Aug 2015 · Science of Advanced Materials
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    Jun-Seong Lee · Akash Katoch · Jae-Hun Kim · Sang Sub Kim
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    ABSTRACT: Networked p-CuO nanowires (NWs) were grown on a patterned electrode pad by the thermal oxidation of an electron-beam-deposited Cu layer. The Au nanoparticles (NPs) were then functionalized on CuO NWs by the heat treatment of an Au layer deposited by sputtering. The diameter of the functionalized Au NPs could be controlled in the range of 20-145 nm by changing the thickness of the deposited Au layers. The sensing properties of the Au-functionalized networked CuO NWs for representative oxidizing (NO2) and reducing (CO) gases were investigated. Au functionalization greatly enhanced the gas-sensing abilities of the CuO NWs. The CuO NWs showed the best sensing properties when they were functionalized with 60 nm-diameter Au NPs. This suggests that the size optimization of the metal NPs for functionalization is essential for obtaining the superior sensing properties of oxide NWs.
    Full-text · Article · Aug 2015 · Sensors and Actuators B Chemical
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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.
    Full-text · Article · Jul 2015 · Sensors and Actuators B Chemical

Publication Stats

3k Citations
504.96 Total Impact Points

Institutions

  • 2007-2016
    • Inha University
      • Department of Materials Science and Engineering
      Incheon, Incheon, South Korea
  • 2015
    • Sungkyunkwan University
      Sŏul, Seoul, 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