K.S. Suh

Korea University, Sŏul, Seoul, South Korea

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Publications (106)246.38 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: High-quality silver (Ag) nanowires with specific dimensions were synthesized by a polyol method with detailed control of the synthesis conditions. For the same amount of AgNO3, the Ag nanowire density became higher as the nanowire diameter decreases and the length increases. This trend was replicated in Ag nanowire films coated on poly(ethylene terephthalate) films and higher densities of Ag nanowires and their junctions were observed in thinner and shorter nanowire networks. Nanowire films with a low sheet resistance (<100 Ω sq−1) and a high transmittance (>90%) resulted from thin, long Ag nanowires. A modified percolation model, which emphasized the importance of the nanowire junction density, was in good agreement with the experimental observations. Meanwhile, long Ag nanowires were found to be undesirable in respect of their uniform coating over a large area. These results offer important design rules of Ag nanowires for highly conductive and transparent nanowire films.
    Acta Materialia. 01/2015; 83.
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    ABSTRACT: For the first time, highly efficient and flexible polymer light emitting diodes (PLEDs) based on silver nanowire (AgNW) electrode, with improved operational stability by simply applying pre-bias conditioning treatment, are demonstrated. Reverse bias conditioning performed before J–V–L measurement of the PLEDs enables the rough AgNW networks to function properly as a bottom electrode by stabilizing current characteristics, and the devices continue to show consistent operational performances. Conditions of applied bias and thicknesses of active layer are controlled for optimization and it is found that high reverse voltage is required to obtain current stabilization. Adequate thickness of polymer is also necessary to avoid breakdown induced by reverse bias. The essential effect of pre-bias conditioning on the improved performances of PLEDs is investigated, and it is found that morphological change of AgNW networks contribute to the improvement in device performance. Some of the AgNWs that appear to be pathway of leakage current are deformed, and surface roughness (RMS) of the AgNW film is decreased while the sheet resistance of the film is maintained when the reverse bias conditioning is applied. It is also revealed that pre-bias conditioning is independent from directionality of the applied bias when utilizing insulating polymer sandwiched between two electrodes.
    Advanced Functional Materials 08/2014; · 10.44 Impact Factor
  • Dongsun Kim, Wonjoon Ho, Kwang S. Suh
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    ABSTRACT: LCD manufacturing processes are often exposed to the electrostatic hazards due to going through various optic film processes. In this paper, we report the electrostatic discharge failure that occurred during the detachment process of protective film to attach consecutive one on a panel. The effects of modified surface treatment on an adhesive layer of the protective film and the entry sequence of the stage to move the following process in the peeling process of protective film were analyzed. The difference of the respective surface properties of the protective film was investigated using scanning electron microscope (SEM) and the electrostatic voltage measurements during a peeling process. The surface characterization of the film, when it is being rubbed and separated from main film, affects the amount and variation of electrostatic charge generation. Modified surface treatment of a protective film showed significant effect to reduce the failure rate and the maximum friction charge. And it was found that changing solely the entry sequence of the following stage with the modified protective film has a residual electrostatic problem. As a result, a main cause of the failure is considered that the variation of the capacitance between the panel and the stage when charges are generated during a peeling process.
    Journal of Electrostatics 06/2014; · 1.00 Impact Factor
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    ABSTRACT: Quantum chemo-resistive vapour sensors have been synthesized from the assembly of magnetic nanoparticles-decorated reduced graphene oxide (Fe3O4-RGO) with poly(3,4-ethylene dioxythiophene) (PEDOT) and poly(ionic liquid) (PIL). This new hybrid sensing material demonstrated enhanced sensitivity, selectivity, signal-to-noise ratio and reduced response time compared to its elementary constituents (also sensitive), which suggests that a positive synergy of properties has been reached through the structuring of the conducting architecture by spray layer-by-layer. The Fe3O4-RGO/PIL-PEDOT sensor exhibited stable and reproducible signals at room temperature for both polar (ethanol, methanol, acetone, water) and non-polar (chloroform, styrene, dichlorobenzene, toluene) volatile organic compounds (VOC), considered as food degradation biomarkers. Since sensor’s responses are still well defined at the ppm level (and may be even at the subppm level) as attested by a SNR around 10, an application such smart packaging could be envisaged.
    Carbon 03/2014; 74:104-112. · 6.16 Impact Factor
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    ABSTRACT: Hybrids of silver nanoparticle-decorated reduced graphene oxide (Ag-RGO) have been prepared with the use of poly(ionic liquid) (PIL) as a versatile capping agent to develop volatile organic compound (VOC) sensors. The hybrid materials of Ag-RGO/PIL were assembled into three-dimensional-laminated nanostructures, where spherical Ag nanoparticles with diameters between 50 and 300 nm were homogeneously distributed on the graphene sheets and interspaced between them. Ag-RGO/PIL sensors were fabricated by spray layer-by-layer technique and used to detect a set of polar (methanol, ethanol, methyl acetate, acetone and water) and non-polar (chloroform, dichlorobenzene, toluene and styrene) organic vapours. Much higher sensitivity and discriminability were obtained for polar vapours although non-polar ones could also be detected. In comparison with either simple reduced graphene oxide or carbon nanotubes (CNT) functionalised by PIL, the hybrid Ag-RGO/PIL-based sensors showed superior performances in terms of sensitivity, selectivity, stability and high reliability. For example, a signal-to-noise ratio up to 168 was obtained for 1 ppm of methanol and signals drift between two experiments spaced out in the time of 3 months was less than 3 %. It is expected that by extrapolation, a limit of detection at the parts per billion level can be reached. These results are promising to design e-noses based on high stability chemoresistive sensors for emerging applications such as anticipated diagnostic of food degradation or diseases by the analysis of VOC, some of them being in this case considered as biomarkers.
    Analytical and Bioanalytical Chemistry 01/2014; 406(16):3995-4004. · 3.66 Impact Factor
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    ABSTRACT: Electric double layer capacitors (or supercapacitors) store charges through the physisorption of electrolyte ions onto porous carbon electrodes. The control over structure and morphology of carbon electrode materials is therefore an effective strategy to render them high surface area and efficient paths for ion diffusion. Here we demonstrate the fabrication of highly porous graphene-derived carbons with hierarchical pore structures in which mesopores are integrated into macroporous scaffolds. The macropores were introduced by assembling graphene-based hollow spheres and the mesopores were derived from the chemical activation with potassium hydroxide. The unique three-dimensional pore structures in the produced graphene-derived carbons gives rise to a Brunauer-Emmett-Teller surface area value of up to 3,290 m2 g-1 and provide efficient pathway of electrolyte ions to diffuse into the interior surfaces of bulk electrode particles. These carbons exhibit both high gravimetric (174 F g-1) and volumetric (~100 F cm-3) specific capacitance in ionic liquid electrolyte in acetonitrile. The energy density and power density of the cell assembled with this carbon electrode are also high with gravimetric values of 74 Wh kg-1 and 338 kW kg-1, and volumetric values of 44 Wh L-1 and 199 kW L-1, respectively. The supercapacitor performance achieved with these graphene-derived carbons is attributed to their unique pore structure and make them potentially promising for diverse energy storage devices.
    ACS Nano 07/2013; · 12.03 Impact Factor
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    ABSTRACT: Large-scale integration of vanadium dioxide (VO2) on mechanically flexible substrates is critical to the realization of flexible smart window films that can respond to environmental temperatures to modulate light transmittance. Up until now, the formation of highly crystalline and stoichiometric VO2 on flexible substrate has not been demonstrated due to the high temperature condition for VO2 growth. Here, we demonstrate a VO2-based thermochromic film with unprecedented mechanical flexibility by employing graphene as a versatile platform for VO2. The graphene effectively function as an atomically thin, flexible, yet robust support which enables the formation of stoichiometric VO2 crystals with temperature-driven phase transition characteristics. The graphene-supported VO2 was capable of being transferred to plastic substrate, forming a new type of flexible thermochromic film. The flexible VO2 films were then integrated into the mock-up house, exhibiting its efficient operation to reduce the in-house temperature under infrared irradiation. These results provide important progress for the fabrication of flexible thermochromic films for energy-saving windows.
    ACS Nano 06/2013; · 12.03 Impact Factor
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    ABSTRACT: The fabrication and design principles for using silver-nanowire (AgNW) networks as transparent electrodes for flexible film heaters are described. For best practice, AgNWs are synthesized with a small diameter and network structures of the AgNW films are optimized, demonstrating a favorably low surface resistivity in transparent layouts with a high figure-of-merit value. To explore their potential in transparent electrodes, a transparent film heater is constructed based on uniformly interconnected AgNW networks, which yields an effective and rapid heating of the film at low input voltages. In addition, the AgNW-based film heater is capable of accommodating a large amount of compressive or tensile strains in a completely reversible fashion, thereby yielding an excellent mechanical flexibility. The AgNW networks demonstrated here possess attractive features for both conventional and emerging applications of transparent flexible electrodes.
    Advanced Functional Materials 03/2013; 23(10). · 10.44 Impact Factor
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    ABSTRACT: A hybrid of graphene and conducting polymer holds great potential as the active materials for high performance chemical sensor application. In this work, a thin hybrid film of reduced graphene oxide (RG-O) and poly(3,4-ethylenedioxythiophene) (PEDOT) was fabricated by means of vapor phase polymerization and explored as active material for chemical sensors. The chemical sensors based on hybrid film of RG-O and PEDOT are capable of detecting electrical signals caused by the absorption of trace levels of different analyte vapors with high sensitivity, selectivity and fast response.
    Organic Electronics 01/2013; 14(11):2789-2794. · 3.84 Impact Factor
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    Synthetic Metals 12/2012; 162(23):2182. · 2.11 Impact Factor
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    Tae Young Kim, Jong Eun Kim, Kwang S. Suh
    Polymer International 10/2012; 61(10). · 2.13 Impact Factor
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    ABSTRACT: We report on a method for the large-scale production of graphene micropatterns by a self-assembly mediated process. The evaporation-induced self-assembly technique was engineered to produce highly ordered graphene patterns on flexible substrates in a simplified and scalable manner. The crossed stripe graphene patterns have been produced over a large area with regions consisting of single- and two-layer graphene. Based on these graphene patterns, flexible graphene-based field effect transistors have been fabricated with an ion-gel gate dielectric, which operates at low voltages of < 2 V with a hole and electron mobility of 214 and 106 cm(2)/V·s, respectively. The self-assembly approach described here may pave the way for the nonlithographic production of graphene patterns, which is scalable to large areas and compatible with roll-to-roll system.
    Nano Letters 02/2012; 12(2):743-8. · 13.03 Impact Factor
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    ABSTRACT: Hybrid materials of Fe3O4-decorated reduced gra- phene oxide (Fe3O4-RGO) and poly(3,4-ethylenedioxythio- phene) (PEDOT) were prepared by poly(ionic liquid)-mediated hybridization. In this hybrid material, poly(ionic liquid) was found to perform multiple roles for: (1) stabilizing Fe3O4-RGO against aggregation in the reaction medium, (2) transferring Fe3O4-RGO nanomaterials from aqueous into organic phase, and (3) associating Fe3O4-RGO nanomaterials with PEDOT. The hybrid materials of Fe3O4-RGO with PEDOT showed the lowest surface resistivity of 80 X sq1 at an RGO-Fe3O4 loading of 1 wt %, and exhibited superparamagnetic behavior with an electromagnetic interference shielding effectiveness of 22 dB.
    Journal of Polymer Science Part A Polymer Chemistry 01/2012; 50(5):927-935. · 3.54 Impact Factor
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    ABSTRACT: Sensing skins made of reduced graphene oxydes (RGO) based quantum resistive vapour sensors (vQRS) have been developed by combining two original processes, i.e., the synthesis of phase transferable graphene sheets using ionic liquid polymers (PIL) and the structuring of 3D conducting architectures by spray layer by layer (sLbL). Many advantages can be derived from this new technology such as versatility of fabrication (sprayability, no need for clean room), flexibility, potential transparency and low cost, making vQRS skins very attractive to develop the next generation of e-noses with quick response time (less than 3 s), room temperature operability, high sensitivity and adjustable selectivity. This can open the door to a wide range of applications, in particular smart packaging, making possible the monitoring of the quality/safety of food by following of VOC biomarkers emitted during its alteration. RGO based QRS are also expected to be biocompatible, exempt of cytotoxycity and the risks of migration of RGO sheets in food must be very limited thanks to their very large surface/thickness ratio and to their embedment into a polymer matrix. Comparing pristine RGO, RGO-PIL and RGO-PIL/PEDOT QRS undoubtedly establishes the superiority of the later in terms of sensitivity and selectivity for the detection of volatile organic solvents (VOC) released from food during its degradation. The reason for this can be found in the unique architecture of the transducer, optimizing functionalization in solution by the combined action of PIL and PEDOT and structuring in the solid state by the assembly step by step in 3D by sLbL.
    Journal of Materials Chemistry 01/2012; 22:21754-21766. · 5.97 Impact Factor
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    ABSTRACT: We present a facile and scalable method for the rapid production of reduced graphene oxide (RG–O) by ionic liquid-assisted microwave chemistry. Microwave irradiation of graphite oxide (GO) in an ionic liquid (IL) enables the rapid reduction of GO within 15 s, producing RG–O containing the IL within their porous structures. The reduced graphene oxide prepared by IL-assisted microwave irradiation (mRG–O) electrodes exhibited a high specific capacitance of 135 F g−1, which can be attributed to the open architecture of the mRG–O filled with IL moieties. A supercapacitor made with mRG–O in an IL electrolyte operated at a voltage of 3.5 V and showed a high energy density (58 W h kg−1) and power density (246 kW kg−1).
    RSC Advances 01/2012; 2:8808-8812. · 3.71 Impact Factor
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    ABSTRACT: We report on an aqueous synthesis of cadmium telluride (CdTe) nanocrystals by using dithiol-functionalized ionic liquids (dTFILs). The dTFILs were designed to have dithiol and vinylimidazolium functional groups and used as a ligand molecule of CdTe quantum dot (QD) to utilize the bidendate chelate interaction afforded by the dithiol groups of dTFILs. The photoluminescence quantum yield of dTFIL-capped CdTe QDs reached up to ~40%, and their luminescent property was maintained for 8 weeks, suggesting an improved stability in water phase. This approach will provide a new synthetic route to the water soluble QDs.
    Journal of Nanomaterials 01/2012; 2012. · 1.55 Impact Factor
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    ABSTRACT: We report a new route for preparing electro-conductive composites based on reduced graphene oxide (RG-O) and poly(3,4-ethylenedioxythiophene) (PEDOT). The composites were prepared by in situ polymerization of EDOT in aqueous mixture containing RG-O platelets modified with poly(sodium 4-styrenesulfonate) (PSS). In the synthetic process, PSS molecules stabilize RG-O in the aqueous phase and function as a polymerization template to hybridize PEDOT chains along RG-O platelets. Compared with the RG-O platelets, the resulting composites show an enhanced electrical conductivity of 9.2 S cm −1 with good thermal stability.
    Polymer International 08/2011; 61:93-98. · 2.13 Impact Factor
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    ABSTRACT: This work presents an approach toward the shape-controlled synthesis of Ag crystals with hierarchical structures by exploitation of ionic liquids (ILs) as a shape-regulating agent. The synthesis of Ag crystals involves the reduction of AgNO(3) by EG in the presence of ILs, specifically 1-butyl-3-methylimidazolium methylsulfate (bmim-MeSO(4)). In accordance with non-classical crystallization growth mechanism, the primary Ag nanoparticles were formed at the early stage of the reaction, and then self-organized into 1D or 3D Ag superstructures via an IL-mediated self-assembly process. Their final morphologies were strongly dependent on the reaction conditions such as the concentration of ILs in the reaction mixture and the reaction temperature, which suggests that ILs play an important role in controlling the shape of the Ag crystals.
    Physical Chemistry Chemical Physics 08/2011; 13(36):16138-41. · 4.20 Impact Factor
  • Advanced Materials 04/2011; 23(24):2734-8. · 14.83 Impact Factor
  • Organic Electronics 01/2011; 12:2215-2224. · 3.84 Impact Factor

Publication Stats

548 Citations
246.38 Total Impact Points

Institutions

  • 1992–2014
    • Korea University
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
  • 2005
    • Chungnam National University
      • Department of Pathology
      Daiden, Daejeon, South Korea
  • 1991–1999
    • Kyung Hee University Medical Center
      Sŏul, Seoul, South Korea
  • 1998
    • Seoul National University
      • School of Chemical and Biological Engineering
      Seoul, Seoul, South Korea
  • 1997
    • Soongsil University
      • Department of Electrical Engineering
      Seoul, Seoul, South Korea
  • 1996–1997
    • Korea Advanced Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 1988–1995
    • University of Connecticut
      • Institute of Materials Science
      Storrs, CT, United States