• Environmental Analysis Health and Toxicology
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• 제30권
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• pp.7.1-7.7
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• 2015

Objectives The widely promising applications of graphene nanomaterials raise considerable concerns regarding their environmental and human health risk assessment. The aim of the current study was to evaluate the toxicity profiling of graphene family nanano-materials (GFNs) in alternative in vitro and in vivo toxicity testing models. Methods The GFNs used in this study are graphene nanoplatelets ([GNPs]-pristine, carboxylate [COOH] and amide [$NH_2$]) and graphene oxides (single layer [SLGO] and few layers [FLGO]). The human bronchial epithelial cells (Beas2B cells) as in vitro system and the nematode Caenorhabditis elegans as in vivo system were used to profile the toxicity response of GFNs. Cytotoxicity assays, colony formation assay for cellular toxicity and reproduction potentiality in C. elegans were used as end points to evaluate the GFNs' toxicity. Results In general, GNPs exhibited higher toxicity than GOs in Beas2B cells, and among the GNPs the order of toxicity was pristine > $NH_2$ > COOH. Although the order of toxicity of the GNPs was maintained in C. elegans reproductive toxicity, but GOs were found to be more toxic in the worms than GNPs. In both systems, SLGO exhibited profoundly greater dose dependency than FLGO. The possible reason of their differential toxicity lay in their distinctive physicochemical characteristics and agglomeration behavior in the exposure media. Conclusions The present study revealed that the toxicity of GFNs is dependent on the graphene nanomaterial's physical forms, surface functionalizations, number of layers, dose, time of exposure and obviously, on the alternative model systems used for toxicity assessment.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3312-3316
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• 2013

Single crystals of hexagonal graphenes were successfully grown on Cu foils using the atmospheric pressure chemical vapor deposition (CVD) method. We investigated the effects of reaction parameters, such as the growth temperature and annealing time, on the size, coverage, and density of graphene domains grown over Cu foil. The mean size of the graphene domains increased significantly with increases in both the growth temperature and annealing time, and similar phenomena were observed in graphene domains grown by low pressure CVD over Cu foil. From the comparison of micro Raman spectroscopy in the graphene films grown with different annealing times, we found that the nucleation and growth of the domains were strongly dependent on the annealing time and growth temperature. Therefore, we confirmed that when reaction time was same, the number of layers and the degree of defects in the synthesized graphene films both decreased as the annealing time increased.

• Current Optics and Photonics
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• 제1권1호
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• pp.7-11
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• 2017

In this study, multilayered graphene was easily transferred to the target substrate in one step using thermal release tape. The transmittance of the transferred graphene according to the number of layers was measured using a spectrophotometer. The sheet resistance was measured using a four-point probe system. Graphene formed using this transfer method showed almost the same electrical and optical properties as that formed using the conventional poly (methyl methacrylate) transfer method. This method is suitable for the mass production of graphene because of the short process time and easy large-area transfer. In addition, multilayered graphene can be transferred on various substrates without wetting problem using the one-step dry transfer method. In this work, this easy transfer method was used for dielectric substrates such as glass, paper and polyethylene terephthalate, and a sheet resistance of ~240 ohm/sq was obtained with three-layer graphene. By fabricating organic solar cells, we verified the feasibility of using this method for optoelectronic devices.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.163.2-163.2
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• 2010

We developed a simple method to synthesis a nitrogen doped graphene, nitrogen plasma treated graphene (NPG) sheets thought nitrogen plasma etching of graphene oxide (GO). X-ray photo electron spectroscopy (XPS) study of NPG sheets treated at various plasma conditions reveal that N-doping is classified to 3 kinds of binding configurations. The nitrogen doping concentration is at least 1.5 at % and up to 3 at% with changing of ratio of nitrogen configuration in NPG. Our group demonstrate ultracapacitor with high capacity and extremely durable using a NPG sheets that are comparable to pristine graphene supercapacitor, and pseudocapacitor using polymer and metal oxide with redox reaction, capacitance that are three-times higher, and a cycle life that are extremely stable. We also realized flexible capacitor by using the paper electrode that are coated by NPG sheets. NPG paper capacitor presented almost same performance compare with NPG on a metal substrate, and durability is much more enhanced than that. To additionally explain that how different kind of atoms in graphene layers can act as the ion absorption sites, we simulated the binding energy between nitrogen in graphene layer and ions in electrolyte. Increasing the energy density and long cycle life of ultracapacitor will enable them to compete with batteries and conventional capacitors in number of applications.

• 한국재료학회지
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• 제31권7호
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• pp.420-426
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• 2021

Graphene, a new material with various advantageous properties, has been actively used in various fields in recent years. Applications of graphene oxide are increasing in combination with other materials due to the different properties of graphene oxide, depending on the number of single and multiple layers of graphene. In this study, single-layer graphene oxide and multi-layer graphene oxide are spray coated on polystyrene, and the physicochemical properties of the coated surfaces are characterized using SEM, Raman spectroscopy, AFM, UV-Vis spectrophotometry, and contact angle measurements. In single-layer graphene oxide, particles of 20 ㎛ are observed, whereas a 2D peak is less often observed, and the difference in surface height increases according to the amount of graphene oxide. Adhesion increases with an increase in graphene oxide up to 0.375 mg, but decreases at 0.75 mg. In multi-layer graphene oxide, particles of 5 ㎛ are observed, as well as a 2D peak. According to the amount of graphene oxide, the height difference of the surface increases and the adhesive strength decreases. Both materials are hydrophilic, but single-layer graphene oxide has a hydrophilicity higher than that of multi-layer graphene oxide. We believe that multi-layer graphene oxide and single-layer graphene oxide can be implemented based on the characteristics that make them suitable for application.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.482-483
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• 2011

Graphene is a good candidate for the future nano-electronic materials because it has excellent conductivity, mobility, transparency, flexibility and others. Until now, most graphene researches are focused on the nano electronic device applications, however, biological application of graphene has been relatively less reported. We have fabricated a deoxyribonucleic acid (DNA) conjugated graphene field-effect transistor (FET) and measured the electrical transport characteristics. We have used graphene sheets grown on Ni substrates by chemical vapour deposition. The Raman spectra of graphene sheets indicate high quality and only a few number of layers. The synthesized graphene is transferred on top of the substrate with pre-patterned electrodes by the floating-and-scooping method [1]. Then we applied adhesive tapes on the surface of the graphene to define graphene flakes of a few micron sizes near the electrodes. The current-voltage characteristic of the graphene layer before stripping shows linear zero gate bias conductance and no gate operation. After stripping, the zero gate bias conductance of the device is reduced and clear gate operation is observed. The change of FET characteristics before and after stripping is due to the formation of a micron size graphene flake. After combined with 30 base pairs single-stranded poly(dT) DNA molecules, the conductance and gate operation of the graphene flake FETs become slightly smaller than that of the pristine ones. It is considered that DNA is to be stably binding to the graphene layer due to the ${\pi}-{\pi}$ stacking interaction between nucleic bases and the surface of graphene. And this binding can modulate the electrical transport properties of graphene FETs. We also calculate the field-effect mobility of pristine and DNA conjugated graphene FET devices.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4022-4029
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• 2022

We investigated the possibility of using graphene for control of hydrogen isotopes by exploring adsorption, reflection, and penetration of hydrogen isotopes on graphene using molecular dynamics. Reflection is the dominant interaction when hydrogen isotopes have low incident energy. Adsorption rates increase with increasing incident energy until 5 eV is reached. After 5 eV, adsorption rates decrease as incident energy increases. At incident energies greater than 5 eV, adsorption rates increase with the number of graphene layers. At low incident energies (<1 eV), no isotopic effects on interactions are observed since the predominant interaction is derived from the force of π electrons. Between 1 eV and 50 eV, heavier isotopes exhibit higher adsorption rates and lower reflection rates than lighter isotopes, due to the greater momentum of heavier isotopes. Adsorption rates are consistently higher when the incident angle of the impacting atoms is smaller between 0.5 eV and 5 eV. At higher energies (>5 eV), larger incident angles lead to higher reflection and lower penetration rates. At high incident energies (>5 eV), crumpled graphene has higher adsorption and lower penetration rates than wrinkled or unwrinkled graphene. The results obtained in this research study will be used to develop novel nanomaterials that can be employed for tritium control.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.380.2-380.2
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• 2014

Direct synthesis of graphene using a chemical vapor deposition (CVD) has been considered a facile way to produce large-area and uniform graphene film, which is an accessible method from an application standpoint. Hence, their fundamental understanding is highly required. Unfortunately, the CVD growth mechanism of graphene on Cu remains elusive and controversial. Here, we present the effect of graphene growth parameters on the number of graphene layers were systematically studied and growth mechanism on copper substrate was proposed. Parameters that could affect the thickness of graphene growth include the pressure in the system, gas flow rate, growth pressure, growth temperature, and cooling rate. We hypothesis that the partial pressure of both the carbon sources and hydrogen gas in the growth process, which is set by the total pressure and the mole fraction of the feedstock, could be the factor that controls the thickness of the graphene. The graphene on Cu was grown by the diffusion and precipitation mode not by the surface adsorption mode, because similar results were observed in graphene/Ni system. The carbon-diffused Cu layer was also observed after graphene growth under high CH4 pressure. Our findings may facilitate both the large-area synthesis of well-controlled graphene features and wide range of applications of graphene.

• Advances in nano research
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• 제8권2호
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• pp.103-114
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• 2020

In this research, buckling and free vibration of rectangular polymeric laminate reinforced by graphene sheets are investigated. Various patterns are considered for augmentation of each laminate. Critical buckling load is evaluated for different parameters, including boundary conditions, reinforcement pattern, loading regime, and laminate geometric states. Furthermore, vibration analysis is investigated for square laminate. Elastic properties of the composite are calculated using a combination of both molecular dynamics (MD) and the rule of mixture (MR). Kinematics of the plate is approximated based on the first shear deformation theory (FSDT). The current analysis is performed based on the energy method. For the numerical investigation, Ritz method is applied, and for shape functions, Chebyshev polynomials are utilized. It is found that the number of layers is effective on the buckling load and natural frequency of laminates which made from non-uniform layers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.391-392
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• 2012

Graphene is a perfectly two-dimensional (2D) atomic crystal which consists of sp2 bonded carbon atoms like a honeycomb lattice. With its unique structure, graphene provides outstanding electrical, mechanical, and optical properties, thus enabling wide variety of applications including a strong potential to extend the technology beyond the conventional Si based electronic materials. Currently, the widespread application for electrostatically switchable devices is limited by its characteristic of zero-energy gap and complex process in its synthesis. Several groups have investigated nanoribbon, strained, or nanomeshed graphenes to induce a band gap. Among various techniques to synthesize graphene, chemical vapor deposition (CVD) is suited to make relatively large scale growth of graphene layers. Direct growth of graphene on hexagonal boron nitride (h-BN) using CVD has gained much attention as the atomically smooth surface, relatively small lattice mismatch (~1.7％) of h-BN provides good quality graphene with high mobility. In addition, induced band gap of graphene on h-BN has been demonstrated to a meaningful value about ~0.5 eV.[1] In this paper, we report the synthesis of grpahene / h-BN bilayer in a chemical vapor deposition (CVD) process by controlling the gas flux ratio and deposition rate with temperature. The h-BN (99.99％) substrate, pure Ar as carrier gas, and $CH_4$ are used to grow graphene. The number of graphene layer grown on the h-BN tends to be proportional to growth time and $CH_4$ gas flow rate. Epitaxially grown graphene on h-BN are characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy.