• Membrane Journal
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• v.25 no.5
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• pp.422-430
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• 2015

The present study announces that the pH value of seed coating solution makes a significant effect on the microstructure of silicalite-1 zeolite layer formed on ${\alpha}$-alumina support. Seed with an average diameter of 75 nm was dispersed in ethanol to prepare three kinds of seed coating solutions with different pH values, and dip-coated on the support. The pH value was controlled to be 2.2, 7.0, and 9.3, respectively. In the secondary growth process, pH 7 seed solution resulted an uniform, 3 to $4{\mu}m$ thick, completely covered, and 100 nm grained silicalite-1 zeolite separation layer. The uniformity and completeness were explained by a uniform, closely packed, multi-layered, and completely covered seed coating in the pH 7 condition. In the condition, ${\alpha}$-alumina support and seed are oppositely charged: support is positively charged (8.4 mV) and seed, negatively (-1.7 mV). The opposite charging induced a strong electrostatic attraction between seed and support, which made the good seed coating state. On the other hand, pH 2.2 and pH 9.3 seed solutions resulted non-uniform, partially covered, and around $1{\mu}m$ grained zeolite separation layer, since seed and support are the same sign charged in the conditions. The same sign charging induced a strong electrostatic repulsion between seed and support which caused a low coverage of seed. It could be concluded that the pH value of seed coating solution is a key parameter to determine the microstructure of silicalite-1 zeolite separation layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.384.1-384.1
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• 2014

대면적 그래핀을 합성하는 방법으로 주로 화학기상증작법, SiC 기판을 고온 열처리하는 방법 그리고 최근에는 고체소스를 활용하여 그래핀을 합성하는 방법 등이 보고되고 있다. 이에, 본 연구에서는 폴리머 용액들을 원하는 기판에 스핀코팅하여 건조시킨 후, 후 열처리 공정을 통해 그래핀을 합성하고 물성을 평가해보았다. 그래핀 합성을 위해서 사용된 폴리머 탄소원은 Vinyl계 폴리머 용액으로, polystyrene (PS), polyacrylonitrile (PAN), 그리고 polymethylmetacrylate (PMMA) 등으로 2wt%의 폴리머 용액을 $SiO_2$기판에 스핀 코팅을 하고, 그 위에 Nickel이나 Copper와 같은 catalytic metal을 capping layer로 증착하고, 고진공에서 후열처리 공정에 의해 그래핀을 성장하였다. 이때, 탄소원으로 쓰인 PS, PMMA 폴리머는 pristine graphene 합성을 위해, PAN 폴리머는 질소가 도핑된(n-type) 그래핀 합성을 위해 사용되었다. 그래핀의 물성은 폴리머 종류, 코팅된 두께, 촉매 금속층 종류와 두께, 그리고 후열처리 공정 온도와 시간에 따라서 조절이 가능하였다. 우리는 Raman spectroscopy, AFM, SEM 등을 활용하여 그래핀의 층수, 결함, 표면양상 등을 평가하였고, 또한 전사된 그래핀을 기반으로 제작된 FET의 게이트 전압에 따른 I-V 곡선을 측정하여 캐리어 종류 및 전하 이동도 등을 평가하였다. 더욱 상세한 내용은 프레젠테이션에서 논하겠다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1376-1380
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• 2007

The charged particle type display have characteristics of high contrast ratio and wide viewing angle, quick response time. We used the yellow(-) and the black(+) colored particles, which is respectively addressed to the cells of upper and rear panel by using electric field. Our independent addressing method has strong points compared to the mixed particle putting method. After addressing, we packaged two panels and did aging process, and then panel is driven by matrix method of four channel electrodes. Layers of particles are controlled by height of cell barriers and needed minimum two layers. When positive voltage is applied to the upper electrode, the yellow particles with negative charge move toward the upper substrate and the black particles with positive charge move toward opposite direction.

• Journal of Adhesion and Interface
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• v.22 no.4
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• pp.153-157
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• 2021

Graphene, a two-dimensional carbon allotrope, has outstanding mechanical and electrical properties. In particular, the charge carrier mobility of graphene is known to be about 100 times higher than that of silicon, and it has received attention as a core material for next-generation electronic devices. However, graphene is very sensitive to environmental conditions, especially vulnerable to moisture or oxygen. It becomes a disadvantage in that the stability of the graphene-based electronic device, so various attempts are being made to solve this problem. In this work, we report a method to greatly improve the stability by controlling the surface energy of the polymer layer used for transferring the insulating layer of the graphene field-effect transistor. As the surface energy of the polymer used as the insulating layer was lowered, the stability could be improved by effectively controlling the adsorption of impurities in the atmosphere such as water molecules or oxygen.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.210-210
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• 2013

그래핀은 뛰어난 기계적, 화학적, 광학적, 전기적 특성을 가지고 있는 2차원 물질로, 대면적 합성법과 전사 공정을 통해 다양한 기판에서의 사용이 가능해지면서 차세대 전자 소자로 활용하기위한 활발한 연구가 이루어지고 있다. 디스플레이, 태양전지의 전극과 전계 효과 트랜지스터의 채널로 적용한 연구에서 우수한 결과들을 보이고 있다. 특히, 금속/금속 산화물 전극은 염료 감응형 태양전지와 유기 발광 다이오드 구조에서 화학적으로 불안정할 뿐 아니라 일함수가 고정되어 쇼트키 접촉이 형성되면 저항을 낮추기 어렵지만, 그래핀은 금속/금속 산화물 전극보다 화학적으로 안정하고 일함수의 조절이 가능해 옴 접촉 형성에 용이하다. 그래핀의 일함수를 조절하는 연구는 크게 공유결합과 비공유 결합을 이용한 방법이 시도된다. 공유 결합을 이용한 방법은 합성과정에서 그래핀의 구조에 내재된 결함 혹은 새로운 결함을 형성하여 다른 원소를 첨가하는 방법이다. 이러한 방법은 그래핀의 결함 영역에서 작용하기 때문에 그래핀 전자 구조의 높은 수준 조절을 위해선 그래핀 구조의 파괴가 동반된다. 반면, 비공유 결합을 이용한 방법은 전하 이동 도핑 효과를 이용해 그래핀의 전자 구조를 제어하는 방법으로, 금속/금속산화물/기능기와 그래핀의 적층으로 복합 구조를 형성하는 방법이다. 금속/금속 산화물과의 복합구조는 안정적인 p-형 도핑이 보고되었지만, n-형 도핑은 대기중의 수분, 산소 그리고 기판과의 상호작용에 의해 대기중에서 불안정해 추가적인 피막공정이 요구된다. 기능기를 이용한 적층 구조는 그래핀과 기판사이의 상호작용 혹은 그래핀 전자 구조를 다양한 기능기를 이용해 제어하는 것으로, 이극성을 가진 자기정렬 단일층(self-assembled monolayers)이 대표적인 방법이다. 공간기(spacer)의 길이나 말단기(end group)의 종류로 p-형과 n-형의 도핑 수준을 제어할 수 있지만, 흡착기(chemisorbing groups)의 반응성이 기판의 화학적, 물리적 표면상태에 의존하기때문에 기판 선택이 제약되며 전처리 공정이 요구될 수 있는 한계가 있다. 본 연구에서는 다양한 기판에 적용가능한 용액 공정을 이용해 그래핀과 고분자를 적층하였고, 안정적이고 효과적으로 일함수를 낮추는 구조를 확인하였다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.55-61
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• 1998

Organic light emitting devices from a single layer thin film with a hole transport polymer, poly(N-vinylcarbazole) (PVK) doped with 2-(4-bi phenyl)-5-(4-t-butyl-phenyl) -1,3,4-oxadiazole (Bu-PBD) as electron transporting molecules and Coumurine 6(C6), 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), Rhodamine B as a emitter dye were fabricated. The sing1e layer structure and the use of soluble materials simplify the fabrication of devices by spin coating technique. The active layer consists of one polymer layer that is simply sandwiched between two electrodes, indium-tin oxide (ITO), and aluminum. In this structure, electron and hole inject from the electrodes to the PVK : Bu-PBD active layer. Respectively, Blue, green and orange colored emission spectrum by the use of TPB, C6, Rhodamine B dye emitted at 481nm, 500nm and 585nm were achieved during applied voltages. PVK materials can be useful as the host polymer to be molecularly doped with other organic dyes of the different luminescence colors. And EL color can be tuned to the full visible wavelength.

• Applied Chemistry for Engineering
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• v.34 no.3
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• pp.258-263
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• 2023

In this study, conductive polymers and the enzyme tyrosinase (Tyr) were deposited on the surface of a screen printed carbon electrode (SPCE), which can be fabricated as a disposable sensor chip, and applied to the detection of bisphenol F (BPF), an endocrine disruptor with proven links to male diseases and thyroid disorders, using electrochemical methods. On the surface of the SPCE working electrode, which was negatively charged by oxygen plasma treatment, a positively charged conductive polymer, poly(diallyldimethyl ammonium chloride) (PDDA), a negatively charged polymer compound, poly(sodium 4-styrenesulfonate) (PSS), and another layer of PDDA were layered by electrostatic attraction in the order of PDDA, PSS, and finally PDDA. Then, a layer of Tyr, which was negatively charged due to pH adjustment to 7.0, was added to create a PDDA-PSS-PDDA-Tyr sensor for BPF. When the electrode sensor is exposed to a BPF solution, which is the substrate and target analyte, 4,4'-methylenebis(cyclohexa-3,5-diene-1,2-dione) is generated by an oxidation reaction with the Tyr enzyme on the electrode surface. The reduction process of the product at 0.1 V (vs. Ag/AgCl) generating 4,4'-methylenebis(benzene-1,2-diol) was measured using cyclic and differential pulse voltammetries, resulting in a change in the peak current with respect to the concentration of BPF. In addition, we compared the detection performance of BPF using an ionic liquid electrolyte as an alternative to phosphate-buffered saline, which has been used in many previous sensing studies. Furthermore, the selectivity of bisphenol S, which acts as an interfering substance with a similar structure to BPF, was investigated. Finally, we demonstrated the practical applicability of the sensor by applying it to analyze the concentration of BPF in real samples prepared in the laboratory.