• Carbon letters
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• v.12 no.4
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• pp.207-217
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• 2011

We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.725-729
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• 2015

Organic light emitting diodes (OLEDs) are regarded as the next generation display and solid-state lighting due to their superb achievements from extensive research efforts on improving the efficiency and stability of OLEDs in addition to developing new materials. Herein, efficient green phosphorescent OLEDs were obtained by using hexaazatrinaphthylene (HAT) derivatives as a hole injection layer. External quantum and current efficiencies of OLEDs were enhanced from 8.8% and 30.8 cd/A to 13.6% and 47.7 cd/A, respectively by inserting a thin layer of HAT derivatives between the ITO and hole transporting layer. The enhancement of OLEDs was found to be originated from the inserted HAT derivatives, which resulted in the optimized hole-electron balance inside the emission layer.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.559-565
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• 2011

The following noble series of statistical copolymers, poly[(2-(3-thienyl)ethanol n-butoxycarbonylmethylurethane)-co-3-hexylthiophene] (PURET-co-P3HT), were synthesized by the chemical dehydrogenation method using anhydrous $FeCl_3$. The structure and electro-optical properties of these copolymers were characterized using $^1H$-NMR, UV-visible spectroscopy, elemental analysis, GPC, DSC, TGA, photoluminescence (PL), and cyclic voltammetry (CV). The statistical copolymers, PURET-co-P3HT (1:0, 2:1, 1:1, 1:2, 1:3), were soluble in common organic solvents and easily spin coated onto indium-tin oxide (ITO) coated glass substrates. Hybrid bulk heterojunction photovoltaic cells with an ITO/G-PEDOT/PURET-co-P3HT:PCBM:Ag nanowires/$TiO_x$/Al configuration were fabricated, and the photovoltaic cells using PURET-co-P3HT (1:2) showed the best photovoltaic performance compared with those using PURET-co-P3HT (1:0, 2:1, 1:1, 1:3). The optimal hybrid bulk heterojunction photovoltaic cell exhibits a power conversion efficiency (PCE) of 1.58% ($V_{oc}$ = 0.82 V, $J_{sc}$ = 5.58, FF = 0.35) with PURET-co-P3HT (1:2) measured by using an AM 1.5 G irradiation (100 mW/$cm^2$) on an Oriel Xenon solar simulator (Oriel 300 W).

• 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.

• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.165-169
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• 2008

It is very important to decompose uniformly the metal film in semiconductor devices process. The thickness uniformity of the ITO film by standard magnetron sputtering system are about $\pm4%\sim\pm5%$ and the center of the wafer is more thick than the edge of the wafer. We designed and made the discharge electrode structure and controlled the direction of sputtering materials in magnetron sputtering system. The thickness uniformity are increased to $\pm0.8\sim1.3%$ in 4" wafer using the new sputtering gun in magnetron sputtering system. In wafer to wafer thickness uniformity, $\pm$5.3% are increased to $\pm$1.5% using the new sputtering gun. The thickness uniformity of the Al film are about $\pm$1.0% using the new sputtering gun in magnetron sputtering system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.309-310
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• 2005

In the fabrication of high performance red organic light emitting diode, 2-TNA TA [4,4',4" -tris (2-naphthylphenyl- phenylamino)-triphenylamine] as hole injection material and N PH [N,N'-bis (1-naphthyl) -N,N' -diphenyl-1, 1'-biphenyl-4,4'- diamine] as hole transport material were deposited on the ITO (indium tin oxide)/glass substrate by vacuum evaporation, And then, red color emission layer was deposited using Alq3 as a host material and Rubrene (5,6,11,12- tetraphenylnaphthacene) and GDI 4234 as dopants. Finally, small molecular weight OLED with the structure of ITO/2-TNATA/ NPB/Alq3+Rubrene+GDI4234/Alq3/LiF/Al was obtained by in-situ deposition of Alq3, LiF and Al as electron transport material, electron injection material and cathode. respectively. Green OLED fabricated in our experiments showed the color coordinate of CIE(0.65,0.35) and the maximum luminescence efficiency of 2.1 lm/W at 7 V with the peak emission wavelength of 632 nm.

• Journal of the Korean Applied Science and Technology
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• v.22 no.4
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• pp.315-322
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• 2005

We investigated the electrochemical properties for Langmuir-Blodgett (LB) films mixed with 4-octyl-4'-(5-carboxylpentamethyleneoxy)azobenzene (denoted as 8A5H) and $phospholipid(L-{\alpha}-dimyristoylphosphatidylcholine$, denoted as DMPC). LB films of 8A5H monolayer and 8A5H-DMPC were deposited by using the Langmuir-Blodgett method on the indium tin oxide(ITO) glass. The electrochemical properties measured by using cyclic voltammetry with a three_electrode system, an Ag/AgCl reference electrode, a platinum wire counter electrode and LB film-coated ITO working electrode at various concentrations(0.1, 0.5, and 1.0mol/L) of $NaClO_4$ solution. A measuring range was reduced from initial potential to -1350mV, continuously oxidized to 1650mV and measured to the initial point. The scan rates were 50, 100, 150 and 200mV/s, respectively. As a result, LB films of 8A5H monolayer appeared irreversible process caused by only the oxidation current from the cyclic voltammogram and LB films of 8A5H-DMPC mixture were found to be caused by a reversible oxidation-reduction process.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.487-487
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• 2011

Recently graphene has emerged as a fascinating 2D system in condensed-matter physics as well as a new material for the development of nanotechnology. The unusual electronic band structure of graphene allows it to exhibit a strong ambipolar electric field effect with high mobility. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ${\sim}60{\Omega}$/sq and ~85 % transmittance in the visible range (400?900 nm), the CVD-grown graphene electrodes have a higher/flatter transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition, for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10 ~ 15 nm in mean size were decorated along the surface of the graphene after 1.5 MeV-e-beam irradiation. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• 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.