• Journal of the Korean Applied Science and Technology
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• v.32 no.4
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• pp.789-794
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• 2015

In this study, we investigated the stability with respect to the Langmuir-Blodgett(LB) monolayer films of stearic acid and phospholipid(L-${\alpha}$-dimyristoylphosphatidyl choline, DMPC) mixture. LB films of stearic acid and DMPC monolayer were deposited by the LB method on the indium tin oxide(ITO) glass. The electrochemical properties measured by cyclic voltammetry with three-electrode system in $0.05N\;NaClO_4$ solution, -0.3 V initial, 1650 mV switching potential and -1350 mV final potential. As a result, monolayer LB films of stearic acid and phospholipid mixture was appeared on irreversible process caused by the oxidation current from the cyclic voltammogram. Diffusion coefficient (D) of stearic acid and DMPC mixture(molar ratio 1:1, 1:2, 1:3) was calculated $1.4{\times}10^{-3}$, $1.7{\times}10^{-3}$ and $1.6{\times}10^{-3}(cm^2/s)$ in $0.05N\;NaClO_4$ solution, respectively.

• Journal of the Korean Applied Science and Technology
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• v.30 no.1
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• pp.64-70
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• 2013

We investigated an electrochemical properties for Langmuir-Blodgett (LB) monolayer films of sphingomyelin and polyamic acid(1:1 molar ratio) mixture. LB monolayer films of mixture was deposited by the LB method on the indium tin oxide(ITO) glass. The electrochemical properties measured by cyclic voltammetry with three-electrode system in $KClO_4$ solution. The current of reduction and oxidation range was measured from 1650 mV to -1350 mV, continuously. The scan rates were 50, 100, 150, 200 and 250 mV/s, respectively. As a result, LB monolayer films of sphingomyelin and polyamic acid mixture was appeared on irreversible process caused by the reduction current from the cyclic voltammogram. Diffusion coefficient (D) in the sphingomyelin and polyamic acid mixture was calculated $2.67cm^2s^{-1}{\times}10^5$, $5.23cm^2s^{-1}{\times}10^6$ at 0.1 N and 0.2 N $KClO_4$ solutions, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.566-566
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• 2012

그래핀(Graphene)은 모든 탄소 동소체의 기본구성 요소로 2 차원 결정구조를 가지며, 양자홀 효과(quantum Hall effect), 뛰어난 열 전도도, 고 탄성, 광학적 투과성 등과 같은 탁월한 물리적 성질을 보이는 물질이다. 이러한 그래핀의 우수한 특성은 전계 효과 트랜지스터(field effect transistor), 화학/바이오 센서, 투명 전극(transparent electrode) 등의 다양한 전자소자를 개발하는 응용 가능하다. 그 중, 그래핀 투명전극의 제조는 가장 응용가능성이 높은 분야이다. 현재 투명전극 물질로는 인듐-주석 산화물(indium tin oxide; ITO)가 널리 이용되고 있으나, 인듐의 고갈로 인한 공급부족 문제 및 고 생산비용, 휘어지지 않는 취성 등의 단점을 지니고 있다. 따라서, 우수한 광학적 투과성과 전기전도성을 지닌 그래핀이 ITO의 대체 물질로서 각광받고 있다.[1-5] 본 연구에서는 그래핀의 투명전도필름의 응용을 위해 면저항을 낮추기 위한 방법으로 화학적 도핑(doping)을 이용하였다. 그래핀은 구리(copper; Cu) 호일을 촉매로 사용하여 열 화학증착법(Thermal Chemical Vapor Deposition)을 이용하여 합성하였다. 합성된 그래핀은 PMMA(Poly(methyl methacrylate)) 전사법을 이용하여 산화실리콘(SiO2) 기판에 전사 후, 염화은(AgCl)과 클로로벤젠(C6H5Cl)으로 만든 콜로이드(colloid) 용액에 디핑(dipping)하여 그래핀에 은 입자를 도핑 하였다. 그 결과, 은 입자 도핑 농도에 따라 면저항이 감소하는 양상을 보였다. 제작된 그래핀 투명전도성 필름의 투과도는 자외선-가시광선-근적외선 분광법(UV-Vis-NIR spectroscopy)를 이용하여 측정하였고, 라만 분광법(Raman spectroscopy)을 통해 그래핀 필름의 질적 우수성과 성장 균일도를 조사하였다.

• Journal of Biomedical Engineering Research
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• v.36 no.6
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• pp.283-290
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• 2015

We proposed blink based online speller for the locked-in syndrome (LIS) patients, paralyzed in nearly all voluntary muscles expect for the eyes, with a simple and easy-to-use eye blink detection glasses. Electrooculogram (EOG) is the golden standard method of eye movement or blink measurement with Ag/AgCl electrodes. However, this method has several drawbacks such as skin irritation and dehydration of conductive gel. To resolve the shortcomings, we used a blink detection system based on a transparent capacitively coupled electrode, which is conductive indium tin oxide (ITO) films. The films make it possible to measure eye blink without direct skin contact and obstruction of field of view. We finally developed user-friendly blink based online speller with the blink detection system. To classify voluntary and non-voluntary blink, we used the double blink for command of the speller. The online speller experiment result with six healthy subjects shows that mean accuracy is 98.96% and letter per minute (LPM) is 4.73, which are better result by comparison with conventional P300 or auditory brain-computer interface (BCI) paradigm. The result of the experiment demonstrates the possibility of applying the proposed system as a communication method for the LIS patients.

• Journal of the Korean Applied Science and Technology
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• v.31 no.3
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• pp.352-358
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• 2014

We were investigated the stability through the electrochemical characteristics of saturated fatty acid(C12, C14, C16, C18) monolayer LB films by cyclic voltammetry. Saturated fatty acid monolayer LB films was deposited on the indium tin oxide(ITO) glass by the LB method. The electrochemical properties were measured by cyclic voltammetry with a three-electrode system in 0.1 N $NaClO_4$ solution. The measuring range was continuously oxidized to 1650 mV, with an initial potential of -1350 mV was reduced. Scanning rates of 50, 100, 150, 200, and 250 mV/s were set. As a result, LB monolayer films of saturated fatty acid were appeared on irreversible processes by the oxidation current from the cyclic voltammogram. Diffusion coefficient(D) of saturated fatty acid(C12, C14, C16, and C18) was calculated 22.231, 2.461, 7.114 and 2.371 ($cm^2s^{-1}{\times}10^{-4}$) in 0.1 N $NaClO_4$ solution, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.1
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• pp.29-33
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• 2018

Flexible electronics must be stable under various deformations such as bending, folding, and rolling. The reliability of ITO (Indium Tin Oxide) film used widely as a transparent electrode for flexible electronics has been studied using rolling fatigue test and bending test. During repeated rolling deformations, the electrical resistance was in-situ measured with different number of rotation. During rolling fatigue test, the electrical resistance of ITO film was significantly increased with increasing the number of rotation. As the stress state of ITO film is different according to the relative position of ITO and substrate, the rolling fatigue test was investigated under both outer and inner bending conditions. Inner rolling fatigue test showed superior electrical stability because the crack nucleation and propagation were retarded under compressive stress state.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.433.1-433.1
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• 2014

The research of graphene, a monolayer of carbon atoms with honeycomb lattice structure, has explosively increased after appeared in 2004. As a result, its high transmittance, mobility, thermal conductivity, and outstanding mechanical and chemical stability have been proved. Especially, many researches were executed about the field of transparent electrode highlighting material of substituting the indium tin oxide (ITO). In addition, qualitative and quantitative improvements have been achieved due to many synthesis methods were discovered. Among them, mostly used method is chemical vapour deposition of graphene grown on copper or nickel. The transmittance, mobility, sheet resistance, and other many properties are completely changed according to these two types of synthesis method of graphene. In this research, considering the difference of characteristics as the synthesis method of graphene, what types of graphene should be used and how to use it were studied. The stacked graphene harvested on copper and multi-layer graphene harvested on nickel were compared and analyzed, as a result, the transmittance of 90% and the sheet resistance of $70{\Omega}{\square}$ was showed even though stacked graphene layers were 4 layers. The reason that could bring these results is lowered sheet resistance due to stacked monolayer graphenes. Moreover, light output power of the three stacked graphene spreading layer shows the highest value, but light-emitting diode with multi-layer graphene died out from 12mA due to also its high sheet resistance. Therefore, we need to clarify about what types of graphene and how to use the graphene in use.

• Transactions on Electrical and Electronic Materials
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• v.16 no.3
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• pp.124-129
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• 2015

Organic electronics are the domain in which the components and circuits are made of organic materials. This new electronics help to realize electronic and optoelectronic devices on flexible substrates. In recent years, organic materials have replaced conventional semiconductors in many electronic components such as, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic (OPVs). It is well known that organic light emitting diodes (OLEDs) have many advantages in comparison with inorganic light-emitting diodes LEDs. These advantages include the low price of manufacturing, large area of electroluminescent display, uniform emission and lower the requirement for power. The aim of this paper is to model polymer LEDs and OLEDs made with small molecules for studying the electrical and optical characteristics. The purpose of this modeling process is, to obtain information about the running of OLEDs, as well as, the injection and charge transport mechanisms. The first simulation structure used in this paper is a mono layer device; typically consisting of the poly (2-methoxy-5(2'-ethyl) hexoxy-phenylenevinylene) (MEH-PPV) polymer sandwiched between an anode with a high work function, usually an indium tin oxide (ITO) substrate, and a cathode with a relatively low work function, such as Al. Electrons will then be injected from the cathode and recombine with electron holes injected from the anode, emitting light. In the second structure, we replaced MEH-PPV by tris (8-hydroxyquinolinato) aluminum (Alq₃). This simulation uses, the Poole-Frenkel -like mobility model and the Langevin bimolecular recombination model as the transport and recombination mechanism. These models are enabled in ATLAS- SILVACO. To optimize OLED performance, we propose to change some parameters in this device, such as doping concentration, thickness and electrode materials.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.319-325
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• 1999

Direct current(d.c.)leakage current voltage characteristics of radio-frequencymagnetron sputtered BaTa\sub 2\O\sub 6\ film capacitors with aluminum(A1) top and indium tin oxide (ITO) bottom electrodes have been investigatedas a function of applied field and temperature. In order to study surfacetreatment effect on the electrical characteristics of as-deposited film weperformed exposure of oxygen plasma on $BaTa_2O_6$ surface. d. c.current-voltage (I-V), bipolar pulse charge-voltage (Q-V), d. c. current-time (I-t) andcapacitance-frequency (C-f) analysis were performed on films. All ofthe films exhibita low leakage current, a high breakdown field strength (3MV/cm-4.5MV/cm), and high dielectric constant (20-30). From the temperature dependence of leakage current,we can conclude that the dominant conduction mechanism is ascribed toSchottky emission at high electric field (>1MV/cm) and hopping conduction at lowelectric field (<1MV/cm). According to our results, the oxide plasma surfacetreatmenton as-deposited $BaTa_2O_6$ resulted in lowering interfacebarrier height and thus, leakage current when a negative voltage applied to the A1 electrode. This can be explained by reduction of surface contamination via etching surface and filling defects such as oxygen vacancies.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.284-284
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• 2009

We have fabricated semiconductor nanocrystals using phase separation on flexible substrates for future application in QD-LEDs. The phase separation between the CdSe semiconductor nanocrystals and TPD organic underlayer can occur during the solvent drying, and the CdSe may rise towards the surface of the coated films, which is arranged into close packed array called self-assembly process. In this work, the polyethylene naphthalate (PEN) films of $200{\mu}m$ thickness was used as a flexible substrate, which was coated with indium tin oxide(ITO) as a transparent electrode of <$15{\Omega}/cm^2$. A number of solvents such as chloroform, toluene, and hexane was used and their coating properties were investigated using the spin coating process. The dispersion of both QD and TPD was rather poor in toluene and hexane and resulted in rougher surface and some aggregates. Meanwhile, the surface roughness of templates can be a very critical issue in the fabrication of QD-LED devices. Some experiments was performed to reduce the ~4nm surface roughness of the PEN films and It can be decreased to the minimum of ~0.7nm. Also discussed are the optical properties of semiconductor nanocrystals used in this phase separation and possible large area and continuous coating process for future application.