• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.313-313
• /
• 2016

Transparent conductive oxide (TCO) films have many disadvantages, such as rarity, possible exhaustion, process temperature limitations, and brittleness on a flexible substrate. In particular, as display technology moves toward flexible displays, TCO will become completely unsuitable due to its brittleness. To address theses issue, many researchers have been studying TCO substitutes. In recent efforts, metal nanowires, conducting polymers, carbon nanotube networks, graphene films, hybrid thin films, and metal meshes/grids have been evaluated as candidates to replace TCO electrodes. In this study, we fabricated the TCO film with Ag meshes shape using polystyrene (PS) beads monolayer on the substrate. The PS beads were used as a template to create the mesh pattern. We fabricated the monolayer on the flexible substrate (PES) with the well-aligned PS beads. Electrodes with Ag mesh shape were formed using this patterned monolayer. We could fabricated the Ag mesh electrode with the sheet resistance with $8ohm{\Omega}/{\Box}$.

• Transactions on Electrical and Electronic Materials
• /
• v.16 no.5
• /
• pp.274-279
• /
• 2015

Reduced graphite oxides (rGOs) were prepared by the common graphite oxidation method and the subsequent reductions. The reduction of graphite oxides (GOs) was conducted chemically and/or thermally. To further reduce the as-prepared rGOs, GOs were treated with chemical/thermal reductions or thermal/chemical reductions, in which the reduction sequence was also considered. The structural changes of as-prepared rGOs, depending on reduction methods, were investigated by X-ray diffraction analyses, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. In addition, we discuss the structural change of the rGOs and their closely related physical and electrical properties, such as thermogravimetry, nitrogen adsorption isotherm, and sheet resistance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.384-384
• /
• 2008

그라핀 기판 제작을 위해서는 그라파이트의 탈착이 가장 핵심 기술이다. 본 연구에서는 신뢰성 있는 그라핀 기판 제작을 위해서, HOPG(Highly Ordered Pyrolytic Graphite) 기판에 고농도의 이온을 주입하고, HOPG를 이형기판에 본딩한후, 후속 열처리를 통해 HOPG를 탈착시켜 그리핀을 얻는 일련의 기본 실험에 대한 결과를 보여 주고자 한다. 기대하는 효과는 고농도의 수소/산소 이온의 경우 주입된 고농도의 수소/산소가 후속 열처리동안 이동 및 뭉침현상을 통해 HOPG기판 내에 수소압력(혹은 CO2 발생)을 증가시켜 HOPG를 자르는 것을 기대하고 있다. 일차 수소이온 주입의 실험결과, 기대와는 달리 $900^{\circ}C$ 열처리에도 절단현상이 발견되지 않아서 산소이온주입에 대한 추가실험을 진행 중이다. 그라핀 본딩의 경우 그라핀의 큰 roughness로 인해 $SiO_2$만의 Fusion 본딩은 불가능함을 여러 실험을 통해 알 수 있었고, 현재 SiO2/SOG 혹은 SiO2/Fox를 이용한 본딩실험을 진행중이다.

• Proceeding of EDISON Challenge
• /
• 2014.03a
• /
• pp.446-449
• /
• 2014

Carbon Nanotube (CNT) have been intensively investigated since they have been considered as building blocks of nanoscience and nanotechnology. Theoretical and computational studies on CNTs have revealed their physical and chemical properties and helped researchers build various experimental devices to study them in depth. However, there have been only few systematic studies on detailed changes in electronic structures of CNTs due to geometrical structure modifications. In this regard, it is necessary to perform systematic investigations of the modifications in electronic structures of CNTs, as their geometrical configurations are altered, using the first-principles density functional theory. In other words, it is essential to determine the true equilibrium structure of CNTs. In this work, we considered the different atomic configurations by maintaining their symmetries, but changing all the inequivalent bonding types one by one. Furthermore, as for CNTs, for example, the way the graphene sheet is wrapped is represented by a pair of indices (n,m) and electronic structures of CNTs vary depending on different indices. Our results suggest all the significant couplings between electronic and geometric structures in CNTs.

• Korean Journal of Materials Research
• /
• v.25 no.7
• /
• pp.341-346
• /
• 2015

The feasibility of obtaining graphitic carbon films on targeted substrates without a catalyst and transfer step was explored through the pyrolysis of the botanical derivative camphor. In a horizontal quartz tube, camphor was subjected to a sequential process of evaporation and thermal decomposition; then, the decomposed product was deposited on a glass substrate. Analysis of the Raman spectra suggest that the deposited film is related to unintentionally doped graphitic carbon containing some $sp-sp^2$ linear carbon chains. The films were transparent in the visible range and electrically conductive, with a sheet resistance comparable to that of graphene. It was also demonstrated that graphitic films with similar properties can be reproduciblyobtained, while property control was readily achieved by varying the process temperature.

• Advances in nano research
• /
• v.13 no.2
• /
• pp.113-120
• /
• 2022

In this paper, a finite element (FE) simulation has been developed in order to examine the nonlinear stability of reinforced sandwich beams with graphene oxide powders (GOPs). In this regard, the nonlinear stability curves have been obtained asuming that the beam is under compressive loads leading to its buckling. The beam is considered to be a three-layered sandwich beam with metal core and GOP reinforced face sheets and it is rested on elastic substrate. Moreover, a higher-order refined beam theory has been considered to formulate the sandwich beam by employing the geometrically perfect and imperfect beam configurations. In the solving procedure, the utalized finite element simulation contains a novel beam element in which shear deformation has been included. The calculated stability curves of GOP-reinforced sandwich beams are shown to be dependent on different parameters such as GOP amount, face sheet thickness, geometrical imperfection and also center deflection.

• Membrane Journal
• /
• v.25 no.1
• /
• pp.67-74
• /
• 2015

In this study the nanofiber was prepared by electrospinning method with polyvinylidene fluoride (PVdF) and a completely dispersed solution of graphene oxide (GO) in the mixed solvent of dimethylformamide (DMF) and acetone. The $0.4{\mu}m$ pore size microfiltration flat membrane was made by increasing layers of the PVdF/GO composite nanofiber. Also, transmembrane pressure (TMP) was measured in order to evaluate fouling of the PVdF/GO composite membrane which was introduced GO reducing biological fouling with the intrinsic antibacterial characteristics. The permeate experiments were carried out simultaneously for the PVdF/GO and commercialized CPVC (chlorinated polyvinyl chloride) flat membranes with $0.01m^2$ effective area in the activated sludge solution of MLSS 4,500 mg/L. TMP of PVdF/GO membrane decreased up to 79% lower than that of CPVC for $10L/m^2{\cdot}h$ permeate flux without air supply. Also, for the case of run/stop operational mode, TMP of PVdF/GO membrane decreased up to 69% lower than that of CPVC for $10L/m^2{\cdot}h$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.351-352
• /
• 2011

그래핀(Graphene)은 2차원 평면구조의 $sp^2$ 탄소 결합으로 이루어진 물질이다. 일반적으로 그래핀은 탄소 원자 한층 정도의 얇은 두께를 가지면서 강철의 100배 이상 높은 강도, 다이아몬드보다 2배 이상 뛰어난 열 전도성, 그리고 규소보다 100배 이상 빠른 전자이동도 등의 매우 우수한 특성을 지닌다. 그래핀을 합성하거나 얻는 방법에는, 기계적 박리법(Micro mechanical exfoliation), 산화흑연(graphite oxide)을 이용한 reduced graphene oxide(RGO)방법과 탄화 규소(SiC)를 이용한 epitaxial growth 방법 등이 있지만, 대 면적화가 어렵거나 구조적 결함이 큰 문제점이 있다. 반면, 탄화수소(hydrocarbon)를 탄소 공급원으로 하는 열화학 기상 증착법(Thermal chemical vapor deposition, TCVD)은 구조적 결함이 상대적으로 적으면서 대 면적화가 가능하다는 이점 때문에 최근 가장 많이 이용되고 있는 방법이다. TCVD를 이용, 니켈, 몰리브덴, 금, 코발트 등의 금속에서 그래핀 합성연구가 보고되었지만, 대부분 수 층(fewlayer)의 그래핀이 합성되었다. 하지만, 구리 촉매를 이용하는 것이 단층 그래핀 합성에 매우 효율적이라는 연구결과가 보고되었다. 구리의 경우, 낮은 탄소융해도(solubility of carbon) 때문에 표면에서 self limiting 과정을 통하여 단층 그래핀이 합성된다. 그러나 단층 그래핀 일지라도 면저항(sheet resistance)이 매우 높고, 이론적 계산값에 비해 전자이동도(electron mobility)가 낮게 측정된다. 이러한 원인은 구조적 결함에서 기인된 것으로써 산업으로의 응용을 어렵게 만들기 때문에 양질의 단층 그래핀 합성연구는 필수적이다[1,2]. 본 연구에서는 TCVD를 이용하여 구리 포일(25 ${\mu}m$, Alfa Aeser) 위에 메탄가스를 탄소공급원으로 하여 수소를 함께 주입하고, 메탄가스의 양과 합성시간, 열처리 시간을 조절하면서 균일한 단층 그래핀을 합성하였다. 합성된 그래핀을 $SiO_2$ (300 nm)기판위에 전사(transfer)후 라만 분광법(raman spectroscopy)과 광학 현미경(optical microscope)을 통하여 분석하였다. 그 결과, 열처리 시간이 증가할수록 촉매로 사용된 구리 포일의 grain size가 커짐을 확인하였으며, 구리 포일 위에 합성된 그래핀의 grain size는, 구리 포일의 grain size에 의존하여 커짐을 확인하였다. 또한 동일한 grain 내의 그래핀은 균일한 층으로 합성되었다. 이는 기계적 박리법, RGO 방법, epitaxial growth 방법으로 얻은 그래핀과 비교하여 매우 뛰어난 결정성을 지님이 확인되었다. 본 연구를 통하여 면적이 넓으면서도 결정성이 매우 뛰어난 양질의 단층 그래핀 합성 방법을 확립하였다.

• Journal of the Korean Chemical Society
• /
• v.61 no.1
• /
• pp.16-24
• /
• 2017

The adsorption of various atmospheric harmful gases ($CO_x$, $NO_x$, $SO_x$) on graphene-like boron nitride(BN) and aluminum nitride(AlN) sheets was theoretically investigated using density functional theory (DFT) and MP2 methods. The structures were fully optimized at the $B3LYP/6-31G^{**}$ and $CAM-B3LYP/6-31G^{**}$ levels of theory and confirmed to be a local minimum by the calculation of the harmonic vibrational frequencies. The MP2 single-point binding energies were computed at the $CAM-B3LYP/6-31G^{**}$ optimized geometries. Also the zero-point vibrational energy (ZPVE) and 50%-basis set superposition error (BSSE) corrections were included. The adsorptions of gases on the BN sheet were predicted to be a physisorption process and the adsorptions of gases on the AlN sheet were predicted to be a physisorption process for $CO_x$ and $NO_x$ but to be a chemisorption process for $SO_x$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.314-314
• /
• 2013

Recently, flexibility is one of the hottest issues in the field of electronic devices. For flexible displays or solar cells, a development of transparent conductive electrodes (TCEs) with flexibility, bendability and foldability is an essential element. Hundreds of nanometers indium-tin-oxide (ITO) films have been widely used and commercialized as a transparent electrode, but their brittleness make them difficulty to apply flexible electronics. Many researchers have been studying for flexible TCEs such as a few layers of graphene sheets, carbon nanotube networks, conductive polymer films and combinations among them. Although gained flexibility, their transmittance and resistivity have not reached those of commercialized ITO films. Metal grids electrode cannot act as TCEs only, but they can be used to lower the resistance of TCEs with few losses of transmittance. However, the possibility of device shortage will be rise at the devices with metal grids because a surface flatness of TCEs may be deteriorated when metal grids are introduced using conventional methods. In our research, we have developed hybrid TCEs, which combined tens of nanometers ITO film and metal grids which are embedded in flexible substrate. They show $13{\Omega}$/${\Box}f$ sheet resistance with 94% of transmittance. Moreover, the sheet resistance was maintained up to 1 mm of bending radius. Also, we have verified that flexible organic light emitting diodes and organic solar cells with the TCEs showed similar performances compared to commercial ITO (on glass substrate) devices.