Publications (20)96.23 Total impact
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Article: High-performance graphene-based transparent flexible heaters.
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ABSTRACT: We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters. Time-dependent temperature profiles and heat distribution analyses show that the performance of graphene-based heaters is superior to that of conventional transparent heaters based on indium tin oxide. In addition, we confirmed that mechanical strain as high as ∼4% did not substantially affect heater performance. Therefore, graphene-based, flexible, transparent heaters are expected to find uses in a broad range of applications, including automobile defogging/deicing systems and heatable smart windows.Nano Letters 11/2011; 11(12):5154-8. · 13.20 Impact Factor -
Article: Detection of acetone vapor using graphene on polymer optical fiber.
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ABSTRACT: Recently, many studies have been focused on the development of fiber optic sensor systems for various gases and vapors. In the present study, an intrinsic polymer optical fiber (POF) sensor using graphene is described for the purpose of acetone vapor sensing for the first time. Observations on the continuous measurement of acetone vapor in dehydrated air are presented. The principle of operation of sensor transduction relies on the dependence of the reflectance on the optical and geometric properties of the sensitive over layered when the vapor molecules are adsorbed on the graphene film. For the same purpose the CVD synthesized graphene film was transferred on the POF end. The synthesized graphene film thickness was evaluated using atomic force microscopy (AFM), Raman spectroscopy and transmission electron microscopy (TEM). For the preliminary evaluation using volatile organic compounds, we evaluated the sensor performance for acetone. Upon the interaction of the sensor with acetone vapor, the variation in the reflected light was monitored as a function of the acetone concentration. The sensor response shows a significant change in sensitivity as compared with the POF probe without a graphene coating. The present sensor shows a satisfactory response upon exposure to various concentrations of acetone vapor from 44 ppm to 352 ppm. To the best of our knowledge, the use of graphene film along with POF for the sensing of volatile organic compounds has not previously been reported.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5939-43. · 1.56 Impact Factor -
Article: Flow-dependent directional growth of carbon nanotube forests by chemical vapor deposition.
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ABSTRACT: We demonstrated that the structural formation of vertically aligned carbon nanotube (CNT) forests is primarily affected by the geometry-related gas flow, leading to the change of growth directions during the chemical vapor deposition (CVD) process. By varying the growing time, flow rate, and direction of the carrier gas, the structures and the formation mechanisms of the vertically aligned CNT forests were carefully investigated. The growth directions of CNTs are found to be highly dependent on the nonlinear local gas flows induced by microchannels. The angle of growth significantly changes with increasing gas flows perpendicular to the microchannel, while the parallel gas flow shows almost no effect. A computational fluid dynamics (CFD) model was employed to explain the flow-dependent growth of CNT forests, revealing that the variation of the local pressure induced by microchannels is an important parameter determining the directionality of the CNT growth. We expect that the present method and analyses would provide useful information to control the micro- and macrostructures of vertically aligned CNTs for various structural/electrical applications.Nanotechnology 03/2011; 22(9):095303. · 3.98 Impact Factor -
Article: Transparent conductive film fabrication using intercalating silver nanoparticles within carbon nanotube layers.
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ABSTRACT: Carbon nanotubes have received attention as alternative materials to indium tin oxide for application in transparent conductive films. Their electrical conductivity, however, still has to be improved. In this study, a layer-by-layer self-assembly process was demonstrated using nano-silver-coated carbon nanotubes, which help improve electrical conductivity. The method was based on the pi-pi interaction between the side walls of the carbon nanotubes and nano-silver clusters that were functionalized with benzyl mercaptan. The self-assembled nano-silver cluster monolayer on the surface of the nanotubes can reduce the interfacial contact resistance, thereby leading to high conductivity at a high transparency. The compound was characterized via scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and the four-point probe method.Journal of Nanoscience and Nanotechnology 01/2011; 11(1):489-93. · 1.56 Impact Factor -
Article: A statistical study on nanoparticle movements in a microfluidic channel.
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ABSTRACT: Microfluidic channels have received much attention because they can be used to control and transport nanoscale objects such as nanoparticles, nanowires, carbon nanotubes, DNA and cells. However, so far, practical channels have not been easy to design because they require very expensive fabrication and sensitive experiments. Numerical approaches can be alternatives or supplementary measures to predict the performance of new channels because they efficiently explain nanoscale multi-physics phenomena and successfully solve nanowire alignment and cell adhesion problems. In this paper, a newly updated immersed finite element method that accounts for collision force and Brownian motion as well as fluid-solid interaction is proposed, and is applied to simulate nanoparticle movements in a microfluidic channel. As part of the simulation, Brownian motion effects in a single nanoparticle focusing lens system are examined under different temperature conditions, and the resulting transport efficiencies are discussed. Furthermore, nanoparticle movements in a double focusing lens system are predicted to show the enhancement of focusing efficiency.Journal of Nanoscience and Nanotechnology 01/2011; 11(1):281-5. · 1.56 Impact Factor -
Article: Prediction of anisotropic behavior of nano/micro composite based on damage mechanics with cell modeling.
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ABSTRACT: New advanced composite materials have recently been of great interest. Especially, many researchers have studied on nano/micro composites based on matrix filled with nano-particles, nano-tubes, nano-wires and so forth, which have outstanding characteristics on thermal, electrical, optical, chemical and mechanical properties. Therefore, the need of numerical approach for design and development of the advanced materials has been recognized. In this paper, finite element analysis based on multi-resolution continuum theory is carried out to predict the anisotropic behavior of nano/micro composites based on damage mechanics with a cell modeling. The cell modeling systematically evaluates constitutive relationships from microstructure of the composite material. Effects of plastic anisotropy on deformation behavior and damage evolution of nano/micro composite are investigated by using Hill's 48 yield function and also compared with those obtained from Gurson-Tvergaard-Needleman isotropic damage model based on von Mises yield function.Journal of Nanoscience and Nanotechnology 01/2011; 11(1):619-23. · 1.56 Impact Factor -
Article: Highly conductive, printable and stretchable composite films of carbon nanotubes and silver.
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ABSTRACT: Conductive films that are both stretchable and flexible could have applications in electronic devices, sensors, actuators and speakers. A substantial amount of research has been carried out on conductive polymer composites, metal electrode-integrated rubber substrates and materials based on carbon nanotubes and graphene. Here we present highly conductive, printable and stretchable hybrid composites composed of micrometre-sized silver flakes and multiwalled carbon nanotubes decorated with self-assembled silver nanoparticles. The nanotubes were used as one-dimensional, flexible and conductive scaffolds to construct effective electrical networks among the silver flakes. The nanocomposites, which included polyvinylidenefluoride copolymer, were created with a hot-rolling technique, and the maximum conductivities of the hybrid silver-nanotube composites were 5,710 S cm⁻¹ at 0% strain and 20 S cm⁻¹ at 140% strain, at which point the film ruptured. Three-dimensional percolation theory reveals that Poisson's ratio for the composite is a key parameter in determining how the conductivity changes upon stretching.Nature Nanotechnology 12/2010; 5(12):853-7. · 27.27 Impact Factor -
Article: Roll-to-roll production of 30-inch graphene films for transparent electrodes.
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ABSTRACT: The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.Nature Nanotechnology 08/2010; 5(8):574-8. · 27.27 Impact Factor -
Article: 30 inch Roll-Based Production of High-Quality Graphene Films for Flexible Transparent Electrodes
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ABSTRACT: We report that 30-inch scale multiple roll-to-roll transfer and wet chemical doping considerably enhance the electrical properties of the graphene films grown on roll-type Cu substrates by chemical vapor deposition. The resulting graphene films shows a sheet resistance as low as ~30 Ohm/sq at ~90 % transparency which is superior to commercial transparent electrodes such as indium tin oxides (ITO). The monolayer of graphene shows sheet resistances as low as ~125 Ohm/sq with 97.4% optical transmittance and half-integer quantum Hall effect, indicating the high-quality of these graphene films. As a practical application, we also fabricated a touch screen panel device based on the graphene transparent electrodes, showing extraordinary mechanical and electrical performances.12/2009; -
Article: Numerical simulation of a nanoparticle focusing lens in a microfluidic channel by using immersed finite element method.
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ABSTRACT: Lap-on-a-chip system is one of challenging parts in nano and bio engineering fields, for instance, microfluidic channels on the chip are useful for selecting a target particle and mass transferring of boiomolecules in fluid. However, since experimental approach is highly expensive both in time and cost, alternative reliable methods are required to conceive optimized channels. The purpose of this research is to simulate a nanoparticle focusing lens in a microfluidic channel from nanoparticle control point of view. A promising immersed finite element method is expanded to estimate the path of randomly moving nanoparticles through a focusing lens. The channel flow is assumed as incompressible viscous fluid and Brownian motion effects as well as initial position of particle are quantitatively examined. As a representative result, while the nanoparticles with/without Brownian motion were focused along the center of the channel, the concentration factor representing focusing efficiency was calculated. Therefore, it is expected that the newly proposed numerical method considering Brownian motion will be efficiently applicable to design the microfluidic channel containing various particles, molecules and so forth in the near future.Journal of Nanoscience and Nanotechnology 12/2009; 9(12):7407-11. · 1.56 Impact Factor -
Article: An immunoassay using biotinylated single-walled carbon nanotubes as Raman biomarkers.
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ABSTRACT: A new immunoassay with biotinylated single-walled carbon nanotubes as persistent, non-photobleaching Raman biomarkers demonstrated excellent sensitivity and specificity.The Analyst 08/2009; 134(7):1294-6. · 4.23 Impact Factor -
Article: Optical characterization of DNA-wrapped single walled carbon nanotubes irradiated with ultraviolet light.
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ABSTRACT: We have investigated the effect of ultraviolet irradiation exposure time on single walled carbon nanotubes (SWNTs) wrapped with single-strand DNA (ssDNA) using absorption spectroscopy and Raman spectroscopy. The absorbance value of ssDNA-wrapped SWNTs in aqueous media was found to be decreased, where as SWNTs wrapped with ssDNA with polyd(T) were aggregated under UV irradiation.Journal of Nanoscience and Nanotechnology 11/2008; 8(10):5135-8. · 1.56 Impact Factor -
Article: Effect of slip boundary condition on the design of nanoparticle focusing lenses.
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ABSTRACT: The importance of nanoparticles as a building block for novel application has been emphasized in various fields. Especially, nanoparticle beam has been widely used to measure particle size distribution, synthesize materials, and generate micro-patterns, as it can enhance the measurement resolution and transport efficiency. The aerodynamic lens system has been developed to focus particles in a certain size range. The manufacturing of nanoparticles in gas phase is typically performed at the low pressure conditions and the design and simulation of lens at low pressure have been steadily reported. The computational fluid dynamics (CFD) has been utilized to analyze the flow field and obtain particle trajectories. However, previous work has used no-slip boundary condition at low pressure. This paper describes the lens design and simulation with slip boundary condition at low pressure (approximately 1 Torr). The design of lens is discussed on the basis of the Wang et al.'s guidelines and the commercial code FLUENT is used for simulation. The results of this study show that the difference of particle beam radius between no-slip and slip boundary conditions is 0.03 approximately 0.9 mm for particle size ranging from 3 to 200 nm with Brownian diffusion and that the transport efficiency is slightly higher with slip boundary condition.Journal of Nanoscience and Nanotechnology 08/2008; 8(7):3741-8. · 1.56 Impact Factor -
Article: Optical properties of eu doped M-Ga2S4 (M: Zn, Ca, Sr) phosphors for white light emitting diodes.
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ABSTRACT: Eu2+ doped M-thiogallate (MGa2S4, M: Zn, Ca, Sr) phosphors were prepared by solid-state reaction. The dependence of luminescent properties, photoluminescence and cathodoluminescence, on M2+ ions was investigated. ZnGa2S4: Eu2+, CaGa2S4: Eu2+, and SrGa2S4: Eu2+ exhibited a green emission band at 540 nm, 560 nm, and 535 nm, respectively. The red-shift between CaGa2S4: Eu2+ and SrGa2S4: Eu2+ was originated from the radius difference of Ca2+ and Sr2+ ions. However, it did not apply to ZnGa2S4 : Eu2+ despite of smaller radius of Zn2+ ion. The particle size of ZnGa2S4 : Eu2+ was much smaller than those of the other thiogallates, leading to extremely low CL emission.Journal of Nanoscience and Nanotechnology 12/2007; 7(11):4065-8. · 1.56 Impact Factor -
Article: The evaluation of individual dispersion of single-walled carbon nanotubes using absorption and fluorescence spectroscopic techniques.
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ABSTRACT: We have investigated the degree of dispersion of single-walled carbon nanotubes (SWNTs) in solution using laser spectroscopic techniques. SWNTs were suspended in aqueous media using a sodium dodecyl sulfate (SDS) surfactant. SWNTs with different dispersion states were prepared by controlling the intensity and duration of sonication and centrifugation. The absorption and fluorescence spectroscopic techniques were employed to characterize the different dispersion state of the prepared samples. Nanotube suspensions with better dispersion showed higher fluorescence and sharper absorption peaks. The fluorescence data were characterized as a function of the nanotube chirality, and absorption peak shifts were analyzed depending on the first and second van Hove singularities (vHs) of semiconducting nanotubes.Journal of Nanoscience and Nanotechnology 12/2007; 7(11):3727-30. · 1.56 Impact Factor -
Conference Proceeding: Absorption spectroscopic study of DNA hybridization using single-walled carbon nanotubes
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ABSTRACT: Single walled carbon nanotubes show pronounced sharp UV-vis-NIR absorption peak distributions while they are individually dispersed in aqueous solution phase. In this paper, we present optical absorbance detection of DNA hybridization using developed ssDNA-SWNT conjugates. Hybridization of DNA oligonucleotides with their complementary sequences makes systematic red shifts of linked nanotubes in the near infrared region. Semiconducting tubes exhibit clear responses whereas metallic species do not. The results show that SWNTs may be used to selectively detect specific kinds of DNA oligonucleotides.Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007 -
Article: The DNA hybridization assay using single-walled carbon nanotubes as ultrasensitive, long-term optical labels.
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ABSTRACT: Single walled carbon nanotubes (SWNTs) exhibit strong Raman signals as well as fluorescence emissions in the near infrared region. Such signals do not blink or photobleach under prolonged excitation, which is an advantage in optical nano-biomarker applications. In this paper, we present single-stranded DNA conjugated SWNT probes to locate a particular sequence of DNA within a complex genome. Chromosomal DNAs of human fibroblasts and Escherichia coli are used as a target and a control, respectively. Southern blotting, which uses photostable Raman signals of nanotubes instead of fluorescent dyes, demonstrates excellent sensitivity and specificity of the probes. The results show that SWNTs may be used as generic nano-biomarkers for the precise detection of specific kinds of genes.Nanotechnology 08/2006; 17(14):3442-5. · 3.98 Impact Factor -
Article: Optical detection of DNA hybridization using absorption spectra of single-walled carbon nanotubes
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ABSTRACT: Single-walled carbon nanotubes (SWCNTs) exhibit sharp absorption peak distributions in the UV–vis–nIR range when they are individually dispersed in aqueous solution medium. In this paper, we developed SWCNT-based molecular probes by conjugating single-stranded DNA (ssDNA) with SWCNT. The DNA hybridization event was investigated using the absorption spectra of the ssDNA–SWCNT probes. The results showed that DNA hybridization on the sidewall of SWCNT resulted in systematic red shifts of the absorption spectra of semiconducting nanotubes. However, metallic species did not show any shift in the absorption spectra. The work demonstrated that ssDNA–SWCNTs probes might be used to detect specific kinds of DNA oligonucleotides as optical nano-biosensors.Materials Chemistry and Physics 112(3):738-741. · 2.23 Impact Factor -
Article: Numerical simulation of cylinder oscillation by using a direct forcing technique
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ABSTRACT: Fluid–structure interaction (FSI) is an important safety issue of nuclear components such as reactor vessel internals, heat exchangers, steam generators and piping, etc. For instance, when continuous repetitive flow is rapidly exerted on cylinders, resulting oscillation induces high vibration that may lead to fretting wear on the contact surface of cylinder. In the present research, to assess vibration characteristics of cylinders in fluidic channels, a modified immersed finite element method (IFEM) is developed by using a direct forcing technique coupled with cylinder oscillation. Then, this method is tested for an elastically mounted cylinder in still fluid or subjected to uniform inlet fluid flow and further a simple tube bundle to examine effects of vibration-related parameters.Nuclear Engineering and Design. 240(8):1941-1948. -
Article: The quantitative characterization of the dispersion state of single-walled carbon nanotubes using Raman spectroscopy and atomic force microscopy
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ABSTRACT: A quantitative method to evaluate the degree of dispersion of single-walled carbon nanotubes (SWCNTs), produced by the high-pressure carbon monoxide process, was developed using Raman spectroscopy and atomic force microscopy (AFM). Nanotubes were dispersed in sodium dodecyl sulfate aqueous solution at seven different dispersion states by controlling ultra-sonication and centrifugation parameters. It is known that the intensity of a Raman peak at 267 cm−1, at the excitation wavelength of 785 nm, is qualitatively proportional to the degree of aggregation. Here, we provide a quantitative calibration technique which involves single-layer spin-deposition of SWCNTs on mica substrates and z-scan analysis of AFM. The trend of the height measurements of AFM precisely matched that of the Raman peak at 267 cm−1. Therefore, this approach can be used to quantitatively characterize the dispersion state of SWCNTs.Carbon. 46(12):1530-1534.
Top co-authors
Top Journals
Institutions
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2007–2009
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Sungkyunkwan University
- School of Mechanical Engineering
Seoul, Seoul, South Korea -
Kyonggi University
Seoul, Seoul, South Korea
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2006
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Seoul National University Hospital
Seoul, Seoul, South Korea
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