• KSBB Journal
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• v.27 no.5
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• pp.273-280
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• 2012

Graphene is a one-atom-thick sheet composed of carbon atoms only. It has a two-dimensional honeycomb structure with $sp^2$ orbital bonding, which presents some unique properties. Due to large Young's modulus, good electrical conductivity, ability to immobilize several kinds of small molecules and proteins, and biocompatibility of graphene, it has attracted interests inits ability to enhance cell growth and differentiation, followed by recent several studies. We reviewed about the osteogenic differentiation of mesenchymal stem cells, and neurogenic differentiation of neuron stem cells, and the ectodermal and mesodermal differentiation of induced pluripotent stem cells using graphene. Graphene has not only enhanced the adhesion and proliferation of mesenchymal stem cells, but also led to the faster differentiation even without any other exogenous signals. Nonetheless, graphene has some cytotoxicities in its amount-response manner, which is critical to regenerative medicine. The cytotoxicities of graphene were compared with those of grapheneoxide and carbon nanotubes.

• Ceramist
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• v.22 no.3
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• pp.243-255
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• 2019

Graphene, a two-dimensional material with a single atomic layer, has recently become a major research focus in various applications such as electronic devices, sensors, energy storage, catalysts, and adsorbents, because of its large theoretical surface area, excellent electrical conductivity, outstanding chemical stability, and good mechanical properties. Recently, 3D nanoporous graphene structures have received tremendous attention to expand the application of 2D graphene. Here, we overview the synthesis of 3D nanoporous graphene network structure with two-dimensional graphite oxide sheets, the control of porous parameters such as specific surface area, pore volume and pore size etc, and the modification of electronic structure by heteroatom doping along with its various applications. The 3D nanoporous graphene shows superior performance in diverse applications as a promising key material. Consequently, 3D nanoporous graphene can lead the future for advanced nanotechnology.

• Tribology and Lubricants
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• v.34 no.2
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• pp.60-66
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• 2018

Graphene is a monolayer of carbon atoms (approximately 0.34 nm), arranged in a honeycomb network. It has been hailed as a next-generation flexible and transparent material because it has high electrical and thermal conductivities, excellent mechanical properties, as well as flexible and transparent properties. The wettability of graphene alters its adhesion or surface energy, and it is therefore an important parameter influencing its application in the fabrication of next-generation flexible and transparent electronics. Studies on the wettability of graphene are numerous and various opinions exist. However, almost all of these studies use the wet transfer method to transfer the graphene. In this study, therefore, we investigated the effect of wet and dry transfer methods on water contact angles of graphene on a substrate. The contact angles of substrates vary depending on the type of substrate. It was found that after graphene is transferred to the substrate, regardless of transfer method, the graphene/substrate contact angle increases to a value. The contact angle of graphene transferred using the dry transfer method is higher than the contact angle of graphene transferred using wet transfer methods. The wet transferred graphene is affected by the poly(methyl methacrylate) (PMMA) residue and the polar surface of substrate. The dry transferred graphene is influenced by the conformal contact between graphene and substrate.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.67.1-67.1
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• 2012

Graphene has attracted much attention for future nanoelectronics due to its superior electrical properties. Owing to its extremely high carrier mobility and controllable carrier density, graphene is a promising material for practical applications, particularly as a channel layer of high-speed FET. Furthermore, the planar form of graphene is compatible with the conventional top-down CMOS fabrication processes and large-scale synthesis by chemical vapor deposition (CVD) process is also feasible. Despite these promising characteristics of graphene, much work must still be done in order to successfully develop graphene FET. One of the key issues is the process technique for gate dielectric formation because the channel mobility of graphene FET is drastically affected by the gate dielectric interface quality. Formation of high quality gate dielectric on graphene is still a challenging. Dirac voltage, the charge neutral point of the device, also strongly depends on gate dielectrics. Another performance killer in graphene FET is source/drain contact resistance, as the contact resistant between metal and graphene S/D is usually one order of magnitude higher than that between metal and silicon S/D. In this presentation, the key issues on graphene-based FET, including organic-inorganic hybrid gate dielectric formation, controlling of Dirac voltage, reduction of source/drain contact resistance, device structure optimization, graphene gate electrode for improvement of gate dielectric reliability, and CVD graphene transfer process issues are addressed.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.430-430
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• 2013

Field effect transistor based on semiconductor nanowires has been attracting lots of concerns and studies of scientists because of its different characteristic comparing with other morphology like thin film. Nowadays, graphene is introducing a great promise as an active layer in field effect transistor due to its unique electronic and optoelectronic properties. Thus, a mix structure between etched graphene and semiconductor nanowires is believed to expose novel electrical characteristics. In this study, CuO nanowires (20~80 nm in diameter and $1{\sim}10{\mu}m$ length) were grown during oxidizing Cu foil at $450^{\circ}C$ for 24 h. Besides, 3-layersetched graphene was deposited on Cu foil at $1,000^{\circ}C$ using a feedstock of $CH_4$/$H_2$ mixed gas in CVD system. A structure of Ni/Au electrode + CuO nanowires + etched graphene was fabricated, afterward. Finally, field effect properties of the device was revealed and compared with individual devices of just nanowires and just graphene.

• Journal of Powder Materials
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• v.24 no.4
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• pp.308-314
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• 2017

$Fe_3O_4$/Fe/graphene nanocomposite powder is synthesized by electrical wire explosion of Fe wire and dispersed graphene in deionized water at room temperature. The structural and electrochemical characteristics of the powder are characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, field-emission transmission electron microscopy, cyclic voltammetry, and galvanometric discharge-charge method. For comparison, $Fe_3O_4$/Fe nanocomposites are fabricated under the same conditions. The $Fe_3O_4$/Fe nanocomposite particles, around 15-30 nm in size, are highly encapsulated in a graphene matrix. The $Fe_3O_4$/Fe/graphene nanocomposite powder exhibits a high initial charge specific capacity of 878 mA/g and a high capacity retention of 91% (798 mA/g) after 50 cycles. The good electrochemical performance of the $Fe_3O_4$/Fe/graphene nanocomposite powder is clearly established by comparison of the results with those obtained for $Fe_3O_4$/Fe nanocomposite powder and is attributed to alleviation of volume change, good distribution of electrode active materials, and improved electrical conductivity upon the addition of graphene.

• Journal of Sensor Science and Technology
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• v.32 no.2
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• pp.100-104
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• 2023

In this study, a device was fabricated to check the possibility of a memory device by controlling the oxygen functional groups in graphene oxide formed with a 45-second exposure time. We discovered that graphene oxide can be formed using the ultraviolet (UV) light treatment method with different exposure times. Moreover, Raman spectroscopy measurement revealed that the oxygen functional groups can be moved by controlling the voltage. We further studied the change in the local graphene oxide region, which was found to be related to the modulation of the electrical properties of the device. Therefore, the fabricated graphene oxide device can be used as a wettability switching membrane and graphene-based ion transport device.

• Carbon letters
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• v.14 no.2
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• pp.63-75
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• 2013

Graphene, a carbon crystal sheet of molecular thickness, shows diverse and exceptional properties ranging from electrical and thermal conductivities, to optical and mechanical qualities. Thus, its potential applications include not only physicochemical materials but also extends to biological uses. Here, we review recent experimental studies about graphene for such bioapplications. As a prerequisite to the search to determine the potential of graphene for bioapplications, the essential qualities of graphene that support biocompatibility, were briefly summarized. Then, direct examples of tissue regeneration and tissue engineering utilizing graphenes, were discussed, including uses for cell scaffolds, cell modulating interfaces, drug delivery, and neural interfaces.

• Journal of Sensor Science and Technology
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• v.27 no.3
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• pp.204-208
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• 2018

Monolayer graphene grown via chemical vapor deposition (CVD) is recognized as a promising material for sensor applications owing to its extremely large surface-to-volume ratio and outstanding electrical properties, as well as the fact that it can be easily transferred onto arbitrary substrates on a large-scale. However, the Dirac voltage of CVD-graphene devices fabricated with transferred graphene layers typically exhibit positive shifts arising from transfer and photolithography residues on the graphene surface. Furthermore, the Dirac voltage is dependent on the channel lengths because of the effect of metal-graphene contacts. Thus, large and nonuniform Dirac voltage of the transferred graphene is a critical issue in the fabrication of graphene-based sensor devices. In this work, we propose a fabrication process for graphene field-effect transistors with Dirac voltages close to zero. A vacuum annealing process at $300^{\circ}C$ was performed to eliminate the positive shift and channel-length-dependence of the Dirac voltage. In addition, the annealing process improved the carrier mobility of electrons and holes significantly by removing the residues on the graphene layer and reducing the effect of metal-graphene contacts. Uniform and close to zero Dirac voltage is crucial for the uniformity and low-power/voltage operation for sensor applications. Thus, the current study is expected to contribute significantly to the development of graphene-based practical sensor devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.126-126
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• 2012

Copper is considered to be the most promising substrate, especially Cu(111), for the growth of high quality monolayer graphene. Since interactions between graphene and Cu substrates will influence on the orientation, quality, and electrical properties of synthesized graphene, we experimentally determine a weak interfacial interaction between Cu(111) substrate and graphene using angle-resolved photoemission spectroscopy (ARPES). The measurement was conducted from the initial stage to the formation of a graphene monolayer. Graphene growth was initiated along the Cu(111) lattice, and two rotated graphene domains were grown, where no significant differences were observed in the band structure depending on different orientations. The interaction, including electron transfer from the Cu(111) to graphene, was limited between the Shockley state of the Cu(111) surface and the ${\pi}$ bands of graphene. These results provide direct information on the growth behavior and interactions between the Cu(111) and graphene.