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Han G.H.,Sungkyunkwan Advanced Institute of Nanotechnology | Gunes F.,Sungkyunkwan Advanced Institute of Nanotechnology | Gunes F.,Sungkyunkwan University | Bae J.J.,Sungkyunkwan Advanced Institute of Nanotechnology | And 6 more authors.
Nano Letters | Year: 2011

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts. © 2011 American Chemical Society.


Jeong H.-K.,Sungkyunkwan Advanced Institute of Nanotechnology | Jin M.,Sungkyunkwan Advanced Institute of Nanotechnology | Ra E.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Sheem K.Y.,Samsung | And 3 more authors.
ACS Nano | Year: 2010

We propose a new material for high power and high density supercapacitors with excellent cycle stability. Graphite oxide (PSS-GO) intercalated with poly(sodium 4-styrensulfonate) showed high performance of electric double layer capacitance (EDLC) compared to that of the pristine graphite oxide. Specific capacitance of the PSS-GO reached 190 F/g, and the energy density was much improved to 38 Wh/kg with a power density of 61 W/kg. Cycle test showed that the specific capacitance decreased by only 12% after 14860 cycles, providing excellent cyclic stability. The high EDLC performance of PSS-GO composite was attributed to the wide interlayer distance and simple pore structures accommodating fast ion kinetics. © 2010 American Chemical Society.


Wang J.,Sungkyunkwan Advanced Institute of Nanotechnology | Kwak Y.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee I.-Y.,Sungkyunkwan Advanced Institute of Nanotechnology | Maeng S.,Woosuk University | Kim G.-H.,Sungkyunkwan Advanced Institute of Nanotechnology
Carbon | Year: 2012

Novel chemo-resistive gas sensors based on reduced graphite oxide (rGO) thin films have been fabricated and evaluated for hydrogen detection. The rGO materials were thermally treated at various conditions and analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy techniques to investigate the change of functional groups. The semiconductor type of the rGOs treated at different conditions were checked by flowing hydrogen gas at 20 cm 3/min (sccm) under 10 Torr partial pressure. The rGOs treated at 70 °C in atmosphere (rGO070a), 200 °C in a vacuum (rGO200v), and 500 °C in a vacuum (rGO500v) exhibited n-type, ambipolar, and p-type behavior, respectively. The rGO500v was adopted as active sensing element without any rare metal decoration, and its sensing response to hydrogen was studied by using air as carrier gas. The rGO500v exhibited good sensitivity (∼4.5%), response time (∼20 s), and recovery time (∼10 s) to 160 ppm hydrogen gas at room temperature. © 2012 Elsevier Ltd. All rights reserved.


Maeng I.,University of Seoul | Lim S.,Sungkyunkwan Advanced Institute of Nanotechnology | Chae S.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology | And 2 more authors.
Nano Letters | Year: 2012

We present terahertz spectroscopic measurements of Dirac fermion dynamics from a large-scale graphene that was grown by chemical vapor deposition and on which carrier density was modulated by electrostatic and chemical doping. The measured frequency-dependent optical sheet conductivity of graphene shows electron-density-dependence characteristics, which can be understood by a simple Drude model. In a low carrier density regime, the optical sheet conductivity of graphene is constant regardless of the applied gate voltage, but in a high carrier density regime, it has nonlinear behavior with respect to the applied gate voltage. Chemical doping using viologen was found to be efficient in controlling the equilibrium Fermi level without sacrificing the unique carrier dynamics of graphene. © 2012 American Chemical Society.


Ghosh A.,Sungkyunkwan Advanced Institute of Nanotechnology | Ra E.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Jin M.,Sungkyunkwan Advanced Institute of Nanotechnology | Jeong H.-K.,Daegu University | And 3 more authors.
Advanced Functional Materials | Year: 2011

An ultrathin V2O5 layer was electrodeposited by cyclic voltammetry on a self-standing carbon-nanofiber paper, which was obtained by stabilization and heat-treatment of an electrospun polyacrylonitrile (PAN)-based nanofiber paper. A very-high capacitance of 1308 F g-1 was obtained in a 2 M KCl electrolyte when the contribution from the 3 nm thick vanadium oxide was considered alone, contributing to over 90% of the total capacitance (214 F g-1) despite the low weight percentage of the V2O5 (15 wt%). The high capacitance of the V 2O5 is attributed to the large external surface area of the carbon nanofibers and the maximum number of active sites for the redox reaction of the ultrathin V2O5 layer. This ultrathin layer is almost completely accessible to the electrolyte and thus results in maximum utilization of the oxide (i.e., minimization of dead volume). This hypothesis was experimentally evaluated by testing V2O5 layers of different thicknesses. An ultrathin film of V2O5 is electrodeposited on the surface of carbon nanofibers to obtain a high surface area with an improved electrode conductivity. This provides a high pseudocapacitance of 1308 F g-1 with respect to the effective contribution from the deposited oxide layer. The schematic shows the distribution of V2O5 throughout the nanofiber. The graph shows the dependence of the specific capacitance on the deposited amount of V2O5. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Biswas C.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
Advanced Functional Materials | Year: 2011

Advances in semiconductor device during last few decades enable us to improve the electronic device performance by minimizing the device dimension. However, further development of these systems encounters scientific and technological limits and forces us to explore better alternatives. Low-dimensional carbon allotropes such as carbon nanotube and graphene exhibit superior electronic, optoelectronic, and mechanical properties compared to the conventional semiconductors. This Feature Article reviews the recent progresses of carbon nanotubes and graphene researches and compares their electronic properties and electric device performances. A particular focus is the comparison of the characteristics in transparent conducting films (transparency and sheet resistance) and field-effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET-performance, logic and memory operations). Finally, the performance of devices that combine graphene and carbon nanotubes is also highlighted. Graphene and CNT exhibit excellent electronic and optoelectronic properties. This Feature Article reviews the recent progresses of carbon nanotubes and graphene research and compares their electronic and optoelectronic properties and device performances, such as transparent conducting films (transparency and sheet resistance) and field-effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET-performance, logic and memory operations), in detail. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ghosh A.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
ChemSusChem | Year: 2012

Supercapacitors are one of the key devices for energy-storage applications. They have energy densities much higher than those of conventional capacitors and possess much better power delivery capabilities than batteries. This makes them unique devices that can outperform both batteries and conventional capacitors under special circumstances. Nanocarbons are the main electrode materials for supercapacitors. Abundant sources of nanocarbons and facile processes of modification have led to the fabrication of cheap electrodes. In this review, we focus on the capacitance performance of highly porous activated carbons and attempt to determine the role of different pores. Elaborate discussions are presented on individual contributions from micro- and mesopores and their mutual dependence. This article also presents a comparative performance report for both random and ordered porous nanocarbons. Novel carbon materials, such as carbon nanotubes and graphene, and their contributions in this context are discussed. We summarize key techniques for the functionalization of nanocarbons and their pseudocapacitive charge-storage mechanisms. Nanocarbon composites with redox-active transition-metal oxides and conducting polymers are highlighted along with their impact as electrode materials. Ideal composite structures are highlighted and an attempt is made to determine an ideal future electrode structure for capacitors with high energy and power density. Super power! The capacitance performance of highly porous activated carbons is described and the elucidation of the role of different pores is attempted (see picture). Elaborate discussions are also presented on the individual contributions from micro- and mesopores and their mutual dependence. An ideal electrode can be realized when a charge transportation pathway is obtained through the mesopores that channel ions to the micropores available on the surface. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yu W.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Chae S.H.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee S.Y.,Sungkyunkwan Advanced Institute of Nanotechnology | Duong D.L.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
Advanced Materials | Year: 2011

Ultra-transparent and flexible non-volatile memory devices fabricated using oxygen-decorated graphene electrodes and carbon nanotube network channels are reported. The fabricated memory device revealed a high transmittance of 83.8% with respect to air (PET transmittance: 87.4%) and excellent mechanical stability in a 1000 times bending test. The ultra transparency was realized by introducing oxygen trap sites onto the graphene surface instead of using an opaque inorganic floating gate layer. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lee J.H.,Catholic University of Korea | Jung D.-Y.,Sungkyunkwan Advanced Institute of Nanotechnology
Chemical Communications | Year: 2012

A novel controlled molecular release based on highly oriented nanoplates of layered double hydroxide was fabricated on indium tin oxide substrates by electrophoretic deposition of exfoliated LDH nanosheets. The LDH particle coating exhibited a superior release performance of the order of hours. © 2012 The Royal Society of Chemistry.


Yu W.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
ChemSusChem | Year: 2011

Carbon nanotubes exhibit remarkable mechanical and electronic properties and are, therefore, being regarded as a new functional material for next generation electronics. Nevertheless, several obstacles still exist for an application in industry. The control of carriers in carbon nanotubes is of critical importance prior to an industrial application in transistors. As carbon nanotubes exhibit p-type behavior under ambient conditions, it is difficult to convert them from a p- to an n-type transistor. Also, doping control is a critical issue for applying traditional CMOS technology. Here, we discuss various approaches for preparing operating carbon nanotube transistors: i)impurity doping that employs conventional and interstitial insertion of group III or V materials, ii)chemical doping that induces charge transfer between chemicals and CNTs, iii)carrier control that utilizes the work function difference between metal and CNTs, iv)electrostatic doping that controls the carrier type by using a gate bias, and v)ambipolarity that does not use chemical doping. Advantages and drawbacks of these approaches will be discussed extensively in the text. Have it the carriers way: We discuss various approaches for the doping of operating carbon nanotube transistors: i)impurity doping, ii)chemical doping, iii)control of metal work function, iv) electrostatic doping, and v)ambipolarity. Advantages and drawbacks of these approaches are discussed extensively in the text. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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