• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.338-342
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• 2015

Ripples and charge impurity effect of graphene are considered as the origin of charge puddles in graphene sheet on SiO2. However, this topic is very controversial among researchers in graphene community. In this study, by using density functional theory, we calculate the band structure of the rippled graphene model and charged impurity model that is located close to the (0001) ${\alpha}$-quartz surface. We expect that this study will provide great insight on this matter.

• Carbon letters
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• 제13권4호
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• pp.205-211
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• 2012

Methanol as a carbon source in chemical vapor deposition (CVD) graphene has an advantage over methane and hydrogen in that we can avoid optimizing an etching reagent condition. Since methanol itself can easily decompose into hydrocarbon and water (an etching reagent) at high temperatures [1], the pressure and the temperature of methanol are the only parameters we have to handle. In this study, synthetic conditions for highly crystalline and large area graphene have been optimized by adjusting pressure and temperature; the effect of each parameter was analyzed systematically by Raman, scanning electron microscope, transmission electron microscope, atomic force microscope, four-point-probe measurement, and UV-Vis. Defect density of graphene, represented by D/G ratio in Raman, decreased with increasing temperature and decreasing pressure; it negatively affected electrical conductivity. From our process and various analyses, methanol CVD growth for graphene has been found to be a safe, cheap, easy, and simple method to produce high quality, large area, and continuous graphene films.

• Carbon letters
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• 제27권
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• pp.18-25
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• 2018

In this study, graphene oxide(GO) was used as drug carriers to amorphize poorly watersoluble drugs via a co-spray drying process. Two poorly water-soluble drugs, fenofibrate and ibuprofen, were investigated. It was found that the drug molecules could be in the graphene nanosheets in amorphous or nano crystalline forms and thus have a significantly enhanced dissolution rate compared with the counterpart crystalline form. In addition, the dissolution of the amorphous drug enwrapped with the graphene oxide was higher than that of the amorphous drug in activated carbon (AC) even though the AC possessed a larger specific surface area than that of the graphene oxide. The amorphous formulations also remained stable under accelerated storage conditions ($40^{\circ}C$ and 75% relative humidity) for a study period of 14 months. Therefore, graphene oxide could be a potential drug carrier and amorphization agent for poorly water-soluble drugs to enhance their bioavailability.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.129-129
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• 2016

Graphene, as a single layer of $sp^2$-bonded carbon atoms packed into a 2D honeycomb crystal lattice, has attracted much attention due to its outstanding properties. In order to synthesize high quality graphene, transition metals, such as nickel and copper, have been widely employed as catalysts, which needs transfer to desired substrates for various applications. However, the transfer steps are not only complicated but also inevitably induce defects, impurities, wrinkles, and cracks of graphene. Furthermore, the direct synthesis of graphene on dielectric surfaces has still been a premature field for practical applications. Therefore, cost effective and concise methods for transfer-free graphene are essentially required for commercialization. Here, we report a facile transfer-free graphene synthesis method through nickel and carbon co-deposited layer. In order to fabricate 100 nm thick NiC layer on the top of $SiO_2/Si$ substrates, DC reactive magnetron sputtering was performed at a gas pressure of 2 mTorr with various Ar : $CH_4$ gas flow ratio and the 200 W DC input power was applied to a Ni target at room temperature. Then, the sample was annealed under 200 sccm Ar flow and pressure of 1 Torr at $1000^{\circ}C$ for 4 min employing a rapid thermal annealing (RTA) equipment. During the RTA process, the carbon atoms diffused through the NiC layer and deposited on both sides of the NiC layer to form graphene upon cooling. The remained NiC layer was removed by using a 0.5 M $FeCl_3$ aqueous solution, and graphene was then directly obtained on $SiO_2/Si$ without any transfer process. In order to confirm the quality of resulted graphene layer, Raman spectroscopy was implemented. Raman mapping revealed that the resulted graphene was at high quality with low degree of $sp^3$-type structural defects. Additionally, sheet resistance and transmittance of the produced graphene were analyzed by a four-point probe method and UV-vis spectroscopy, respectively. This facile non-transfer process would consequently facilitate the future graphene research and industrial applications.

• Applied Science and Convergence Technology
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• 제27권2호
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• pp.35-37
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• 2018

The redox reaction on graphene nanoribbon (GNR) field effect transistors(FET) has been studied. In detail, upon employing an electrolyte gating, we verified electron transport performance modulation of GNR FET by monitoring conductance variation under oxidation and reduction processes. The conductance enhancement of GNR via removal of PMMA residue on graphene surface during redox cycles was also observed.

• 센서학회지
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• 제23권4호
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• pp.234-237
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• 2014

In this paper, a copper foil-thick grapheme (thin graphite sheet)-copper foil structure is reported to achieve mechanically strong and high thermal conductive layer suitable for heat spreading components. Since graphene provides much higher thermal conductivity than copper, thick graphene embedded copper layer can achieve higher effective thermal conductivity which is proportional to graphene/copper thickness ratio. Since copper is nonreactive with carbon material which is graphene, chromium is used as adhesion layer to achieve copper-thick graphene-copper bonding for graphene embedded copper layer. Both sides of thick graphene were coated with chromium as an adhesion layer followed by copper by sputtering. The copper foil was bonded to sputtered copper layer on thick graphene. Angstrom's method was used to measure the thermal conductivity of fabricated copper-thick graphene-copper structure. The thermal conductivity of the copper-thick graphene-copper structures is measured as $686W/m{\cdot}K$ which is 1.6 times higher than thermal conductivity of pure copper.

• 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.

• 한국재료학회지
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• 제29권5호
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• pp.304-310
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• 2019

Chemical vapor deposition method using $CH_4$ gaseous hydrocarbons is generally used to synthesize large-area graphene. Studies using non-gaseous materials such as ethanol, hexane and camphor have occasionally been conducted. In this study, large-area graphene is synthesized via chemical vapor deposition using polyethylene as a carbon precursor. In particular, we used a poly glove, which is made of low-density polyethylene. The characteristics of the synthesized graphene as functions of the growth time of graphene and the temperature for vaporizing polyethylene are evaluated by optical microscopy and Raman spectroscopy. When the polyethylene vaporizing temperature is over $150^{\circ}C$, large-area graphene with excellent quality is synthesized. Raman spectroscopy shows that the D peak intensity increased and the 2D peak intensity decreased with increasing growth time. The reason for this is that sp3 bonds in the graphene can form when the correct amount of carbon source is supplied. The quality of the graphene synthesized using polyethylene is similar to that of graphene synthesized using methane gas.

• 한국응용과학기술학회지
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• 제32권2호
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• pp.232-239
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• 2015

화학기상증착법(CVD)을 이용하여 Cu-foil 위에 합성된 대면적의 단층 그래핀(Graphene)을 폴리머 탄성융합체 PDMS(Polydimethylsiloxane)를 이용하여 건식으로 전사하는 기술을 연구하였다. 이때, $UV/O_3$처리를 통해 목표 기판(target substrate)의 표면 개질을 변화시켜 그래핀의 손상이 최소화되로록 그래핀을 전사하였다. 이 과정을 반복 실행하여 그래핀을 다층(1~4 layers)으로 $SiO_2/Si$기판 위에 적층하였으며, 전사된 다층 그래핀의 품질평가를 위하여 광투과율과 면저항의 변화를 측정하였다.

• 한국표면공학회지
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• 제49권1호
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• pp.87-91
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• 2016

The development of high performance transparent electrode with flexibility have been required for flexible electronics. Here, we demonstrate the silver nanowire and reduced graphene oxide hybrid transparent electrode for replacing brittle indium-tin-oxide electrode by spray coating technique and plasma reduction. The spray coating system is applied to deposit silver nanowire and over coated graphene oxide films and it has a great potential to scale-up. The resistance of silver nanowire transparent electrode is reduced by 10% and the surface roughness is decreased after graphene oxide coating. The over-coated graphene oxide is successfully reduced by $H_2$ plasma treatment and it is effective in increasing the environmental stability of electrode. The lifetime of silver nanowire and reduced graphene oxide hybrid electrode at $85^{\circ}C$ of Celsius degree of temperature and 85% of relative humidity has much increased.