Seung Jin Chae - Academia.edu (original) (raw)
Papers by Seung Jin Chae
Journal of Information Display
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Journal of Applied Physics, Jun 15, 2009
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CLEO: 2014, 2014
ABSTRACT We discuss the origin of negative dynamic terahertz (THz) conductivity in graphene. By p... more ABSTRACT We discuss the origin of negative dynamic terahertz (THz) conductivity in graphene. By performing series of fluence and photon-energy dependent studies, we show that the nonequilibrium THz dynamics is strongly affected by the polycrystalline plasmons.
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Nano, 2011
One-step roll-to-roll lamination transfer of graphene was achieved by poly(ethylene co-vinyl acet... more One-step roll-to-roll lamination transfer of graphene was achieved by poly(ethylene co-vinyl acetate) as a binding material which has thermoplastic property and wide rubbery-plateau region between T g ~T m . The transferred graphene film has a transmittance of 96.7% at 550 nm and 1.96 kΩ/sq of sheet resistance measured by simple 4-probe method. Standard deviation was found to be 0.198 kΩ/sq.
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RSC Adv., 2014
We report high-quality GaN crystals grown directly on graphene layers without a buffer layer by m... more We report high-quality GaN crystals grown directly on graphene layers without a buffer layer by metal–organic chemical vapour deposition.
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Scientific reports, 2013
Oscillator-strength sum rule in light-induced transitions is one general form of quantum-mechanic... more Oscillator-strength sum rule in light-induced transitions is one general form of quantum-mechanical identities. Although this sum rule is well established in equilibrium photo-physics, an experimental corroboration for the validation of the sum rule in a nonequilibrium regime has been a long-standing unexplored question. The simple band structure of graphene is an ideal system for investigating this question due to the linear Dirac-like energy dispersion. Here, we employed both ultrafast terahertz and optical spectroscopy to directly monitor the transient oscillator-strength balancing between quasi-free low-energy oscillators and high-energy Fermi-edge ones. Upon photo-excitation of hot Dirac fermions, we observed that the ultrafast depletion of high-energy oscillators precisely complements the increased terahertz absorption oscillators. Our results may provide an experimental priori to understand, for example, the intrinsic free-carrier dynamics to the high-energy photo-excitation,...
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Optics express, Jan 7, 2011
We report GaN-based near ultraviolet (UV) light emitting diode (LED) that combines indium tin oxi... more We report GaN-based near ultraviolet (UV) light emitting diode (LED) that combines indium tin oxide (ITO) nanodot nodes with two-dimensional graphene film as a UV-transparent current spreading electrode (TCSE) to give rise to excellent UV emission efficiency. The light output power of 380 nm emitting UV-LEDs with graphene film on ITO nanodot nodes as TCSE was enhanced remarkably compared to conventional TCSE. The increase of the light output power is attributed to high UV transmittance of graphene, effective current spreading and injection, and texturing effect by ITO nanodots.
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Nature, 2012
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Nano Letters, 2012
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Journal of the American Chemical Society, 2012
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Japanese Journal of Applied Physics, 2011
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Applied Physics Letters, 2011
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Applied Physics Letters, 2013
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Applied Physics Express, 2012
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Advanced Materials, 2011
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Advanced Materials, 2011
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Advanced Materials, 2011
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Advanced Functional Materials, 2012
ABSTRACT In spite of recent successful demonstrations of flexible and transparent graphene heater... more ABSTRACT In spite of recent successful demonstrations of flexible and transparent graphene heaters, the underlying heat-transfer mechanism is not understood due to the complexity of the heating system. Here, graphene/glass defoggers are fabricated and the dynamic response of the temperature as a function of input electrical power is measured. The graphene/glass defoggers reveal shorter response times than Cr/glass defoggers. Furthermore, the saturated temperature of the graphene/glass defoggers is higher than for Cr/glass defoggers at a given input electrical power. The observed dynamic response to temperature is well-fitted to the power-balance model. The response time of graphene/glass defogger is shorter by 44% than that of the Cr/glass defogger. The convective heat-transfer coefficient of graphene is 12.4 × 10−4 W cm−2 °C−1, similar to that of glass (11.1 × 10−4 W cm−2 °C−1) but smaller than that of chromium (17.1 × 10−4 W cm−2 °C−1). The graphene-based system reveals the lowest convective heat-transfer coefficient due to its ideal flat surface compared to its counterparts of carbon nanotubes (CNTs) and reduced graphene oxide (RGO)-based systems.
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ACS Nano, 2011
The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with ... more The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with regard to the roles of cations and anions. Contrary to the general belief that CNTs are p-doped through the reduction of cationic Au(3+) to Au(0), we observed that chlorine anions play a more important role than Au cations in doping. To estimate the effects of Cl and Au on CNTs, the CNT film was dedoped as a function of the annealing temperature (100-700 °C) under an Ar ambient and was confirmed by the sheet resistance change and the presence of a G-band in the Raman spectra. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the doping level of the CNT film was strongly related to the amount of adsorbed chlorine atoms. Annealing at temperatures up to 200 °C did not change the amount of adsorbed Cl atoms on the CNTs, and the CNT film was stable under ambient conditions. Alternatively, Cl atoms started to dissociate from CNTs at 300 °C, and the stability of the film was degraded. Furthermore, the change in the amount of Cl atoms in CNTs was inversely proportional to the change in the sheet resistance. Our observations of the Cl adsorption, either directly or mediated by an Au precursor on the CNT surface, are congruent with the previous theoretical prediction.
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Journal of Information Display
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Bookmarks Related papers MentionsView impact
Journal of Applied Physics, Jun 15, 2009
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CLEO: 2014, 2014
ABSTRACT We discuss the origin of negative dynamic terahertz (THz) conductivity in graphene. By p... more ABSTRACT We discuss the origin of negative dynamic terahertz (THz) conductivity in graphene. By performing series of fluence and photon-energy dependent studies, we show that the nonequilibrium THz dynamics is strongly affected by the polycrystalline plasmons.
Bookmarks Related papers MentionsView impact
Nano, 2011
One-step roll-to-roll lamination transfer of graphene was achieved by poly(ethylene co-vinyl acet... more One-step roll-to-roll lamination transfer of graphene was achieved by poly(ethylene co-vinyl acetate) as a binding material which has thermoplastic property and wide rubbery-plateau region between T g ~T m . The transferred graphene film has a transmittance of 96.7% at 550 nm and 1.96 kΩ/sq of sheet resistance measured by simple 4-probe method. Standard deviation was found to be 0.198 kΩ/sq.
Bookmarks Related papers MentionsView impact
RSC Adv., 2014
We report high-quality GaN crystals grown directly on graphene layers without a buffer layer by m... more We report high-quality GaN crystals grown directly on graphene layers without a buffer layer by metal–organic chemical vapour deposition.
Bookmarks Related papers MentionsView impact
Scientific reports, 2013
Oscillator-strength sum rule in light-induced transitions is one general form of quantum-mechanic... more Oscillator-strength sum rule in light-induced transitions is one general form of quantum-mechanical identities. Although this sum rule is well established in equilibrium photo-physics, an experimental corroboration for the validation of the sum rule in a nonequilibrium regime has been a long-standing unexplored question. The simple band structure of graphene is an ideal system for investigating this question due to the linear Dirac-like energy dispersion. Here, we employed both ultrafast terahertz and optical spectroscopy to directly monitor the transient oscillator-strength balancing between quasi-free low-energy oscillators and high-energy Fermi-edge ones. Upon photo-excitation of hot Dirac fermions, we observed that the ultrafast depletion of high-energy oscillators precisely complements the increased terahertz absorption oscillators. Our results may provide an experimental priori to understand, for example, the intrinsic free-carrier dynamics to the high-energy photo-excitation,...
Bookmarks Related papers MentionsView impact
Optics express, Jan 7, 2011
We report GaN-based near ultraviolet (UV) light emitting diode (LED) that combines indium tin oxi... more We report GaN-based near ultraviolet (UV) light emitting diode (LED) that combines indium tin oxide (ITO) nanodot nodes with two-dimensional graphene film as a UV-transparent current spreading electrode (TCSE) to give rise to excellent UV emission efficiency. The light output power of 380 nm emitting UV-LEDs with graphene film on ITO nanodot nodes as TCSE was enhanced remarkably compared to conventional TCSE. The increase of the light output power is attributed to high UV transmittance of graphene, effective current spreading and injection, and texturing effect by ITO nanodots.
Bookmarks Related papers MentionsView impact
Nature, 2012
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Nano Letters, 2012
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Journal of the American Chemical Society, 2012
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Japanese Journal of Applied Physics, 2011
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Applied Physics Letters, 2011
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Applied Physics Letters, 2013
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Applied Physics Express, 2012
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Advanced Materials, 2011
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Advanced Materials, 2011
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Advanced Materials, 2011
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Advanced Functional Materials, 2012
ABSTRACT In spite of recent successful demonstrations of flexible and transparent graphene heater... more ABSTRACT In spite of recent successful demonstrations of flexible and transparent graphene heaters, the underlying heat-transfer mechanism is not understood due to the complexity of the heating system. Here, graphene/glass defoggers are fabricated and the dynamic response of the temperature as a function of input electrical power is measured. The graphene/glass defoggers reveal shorter response times than Cr/glass defoggers. Furthermore, the saturated temperature of the graphene/glass defoggers is higher than for Cr/glass defoggers at a given input electrical power. The observed dynamic response to temperature is well-fitted to the power-balance model. The response time of graphene/glass defogger is shorter by 44% than that of the Cr/glass defogger. The convective heat-transfer coefficient of graphene is 12.4 × 10−4 W cm−2 °C−1, similar to that of glass (11.1 × 10−4 W cm−2 °C−1) but smaller than that of chromium (17.1 × 10−4 W cm−2 °C−1). The graphene-based system reveals the lowest convective heat-transfer coefficient due to its ideal flat surface compared to its counterparts of carbon nanotubes (CNTs) and reduced graphene oxide (RGO)-based systems.
Bookmarks Related papers MentionsView impact
ACS Nano, 2011
The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with ... more The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with regard to the roles of cations and anions. Contrary to the general belief that CNTs are p-doped through the reduction of cationic Au(3+) to Au(0), we observed that chlorine anions play a more important role than Au cations in doping. To estimate the effects of Cl and Au on CNTs, the CNT film was dedoped as a function of the annealing temperature (100-700 °C) under an Ar ambient and was confirmed by the sheet resistance change and the presence of a G-band in the Raman spectra. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the doping level of the CNT film was strongly related to the amount of adsorbed chlorine atoms. Annealing at temperatures up to 200 °C did not change the amount of adsorbed Cl atoms on the CNTs, and the CNT film was stable under ambient conditions. Alternatively, Cl atoms started to dissociate from CNTs at 300 °C, and the stability of the film was degraded. Furthermore, the change in the amount of Cl atoms in CNTs was inversely proportional to the change in the sheet resistance. Our observations of the Cl adsorption, either directly or mediated by an Au precursor on the CNT surface, are congruent with the previous theoretical prediction.
Bookmarks Related papers MentionsView impact