• 한국재료학회지
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• 제24권12호
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• pp.694-699
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• 2014

We report the chemical vapor deposition growth characteristics of graphene on various catalytic metal substrates such as Ni, Fe, Ag, Au, and Pt. 50-nm-thick metal films were deposited on $SiO_2/Si$ substrates using dc magnetron sputtering. Graphene was synthesized on the metal/$SiO_2$/Si substrates with $CH_4$ gas (1 SCCM) diluted in mixed gases of 10% $H_2$ and 90 % Ar (99 SCCM) using inductively-coupled plasma chemical vapor deposition (ICP-CVD). The highest quality of graphene film was achieved on Ni and Fe substrates at $900^{\circ}C$ and 500 W of ICP power. Ni substrate seemed to be the best catalytic material among the tested materials for graphene growth because it required the lowest growth temperature ($600^{\circ}C$) as well as showing a low ICP power of 200W. Graphene films were successfully grown on Ag, Au, and Pt substrates as well. Graphene was formed on Pt substrate within 2 sec, while graphene film was achieved on Ni substrate over a period of 5 min of growth. These results can be understood as showing the direct CVD growth of graphene with a highly efficient catalytic reaction on the Pt surface.

• 한국분말재료학회지
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• 제24권6호
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• pp.464-471
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• 2017

A metal mesh TCE film is fabricated using a series of processes such as UV imprinting of a transparent trench pattern (with a width of $2-5{\mu}m$) onto a PET film, filling it with silver paste, wiping of the surface, and heat-curing the silver paste. In this work nanosized (40-50 nm) silver particles are synthesized and mixed with submicron (250-300 nm)-sized silver particles to prepare silver paste for the fabrication of metal mesh-type TCE films. The filling of these silver pastes into the patterned trench layer is examined using a specially designed filling machine and the rheological testing of the silver pastes. The wiping of the trench layer surface to remove any residual silver paste or particles is tested with various mixture solvents, and ethyl cellosolve acetate (ECA):DI water = 90:10 wt% is found to give the best result. The silver paste with 40-50 nm Ag:250-300 nm Ag in a 10:90 wt% mixture gives the highest electrical conductance. The metal mesh TCE film obtained with this silver paste in an optimized process exhibits a light transmittance of 90.4% and haze at 1.2%, which is suitable for TSP application.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.53-53
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• 2011

This paper describes results for surface and bulk characterization of the most promising thin film solar cell material for high performance devices, (Ag,Cu) (In,Ga) Se2 (ACIGS). This material in particular exhibits a range of exotic behaviors. The surface and general materials science of the material also has direct implications for the operation of solar cells based upon it. Some of the techniques and results described will include scanning probe (AFM, STM, KPFM) measurements of epitaxial films of different surface orientations, photoelectron spectroscopy and inverse photoemission, Auger electron spectroscopy, and more. Bulk measurements are included as support for the surface measurements such as cathodoluminescence imaging around grain boundaries and showing surface recombination effects, and transmission electron microscopy to verify the surface growth behaviors to be equilibrium rather than kinetic phenomena. The results show that the polar close packed surface of CIGS is the lowest energy surface by far. This surface is expected to be reconstructed to eliminate the surface charge. However, the AgInSe2 compound has yielded excellent atomic-resolution images of the surface with no evidence of surface reconstruction. Similar imaging of CuInSe2 has proven more difficult and no atomic resolution images have been obtained, although current imaging tunneling spectroscopy images show electronic structure variations on the atomic scale. A discussion of the reasons why this may be the case is given. The surface composition and grain boundary compositions match the bulk chemistry exactly in as-grow films. However, the deposition of the heterojunction forming the device alters this chemistry, leading to a strongly n-type surface. This also directly explains unpinning of the Fermi level and the operation of the resulting devices when heterojunctions are formed with the CIGS. These results are linked to device performance through simulation of the characteristic operating behaviors of the cells using models developed in my laboratory.

• 대한의용생체공학회:의공학회지
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• 제36권6호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.450-450
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• 2006

Organic light-emitting diodes (OLED) as pixels for flat panel displays are being actively pursued because of their relatively simple structure, high brightness, and self-emitting nature [1, 2]. The top-emitting diode structure is preferred because of their geometrical advantage allowing high pixel resolution [3]. To enhance the performance of TOLEDs, it is important to deposit transparent top cathode films, such as transparent conducting oxides (TCOs), which have high transparency as well as low resistance. In this work, we report on investigation of the characteristics of an indium tin oxide (ITO) cathode electrode, which was deposited on organic films by using a radio-frequency magnetron sputtering method, for use in top-emitting organic light emitting diodes (TOLED). The cathode electrode composed of a very thin layer of Mg-Ag and an overlaying ITO film. The Mg-Ag reduces the contact resistivity and plasma damage to the underlying organic layer during the ITO sputtering process. Transfer length method (TLM) patterns were defined by the standard shadow mask for measuring specific contact resistances. The spacing between the TLM pads varied from 30 to $75\;{\mu}m$. The electrical properties of ITO as a function of the deposition and annealing conditions were investigated. The surface roughness as a function of the plasma conditions was determined by Atomic Force Microscopes (AFM).

• 공업화학
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• 제5권5호
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• pp.764-771
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• 1994

친핵성용매하에서 p-toluenesulfonic acid나 bezensulfonic acid와 같은 유기산을 지지전해질 겸 dopant로 사용하여 전도성 Polypyrrole필름을 전해중합하였고 분해 특성과 기계적 물성증가에 대하여 고찰하였다. Dimethyformamide/p-toluenesulfonic acid에서 합성한 polypyrrole 필름이 전도도 10-40S/cm, 인장강도 $25N/mm^2$. 연신율은 10%로 가장 좋은 특성을 나타내었다. 또한 전해중합시 최적 조건은 0.5M의 pyrrole과 0.5M의 p-toluenesulfonic acid를 첨가하여 정전류법에서는 $2mA/cm^2$의 전류밀도가, 정전위법으로는 0.9V vs. $Ag/Ag^+$에서 중합할 때였으며 생성된 필름은 공기중에서 안정하였고 도핑, 탈-도핑이 가역적이어서 2차 전지로서의 특성을 갖고 있었다. 온도에 따른 분해과정이 1차 반응으로 dopant 음이온이 분해반응에 관여하지 않아 산화안정성이 좋았으며 분해활성화 에너지는 $1.01JK^{-1}mol^{-1}$, $25^{\circ}C$에서의 분해속도상수는 $3.1{\times}10-7min^{-1}$였다. 여러 가지 host polymer와의 composite를 검토한 결과 인장강도는 50%, 연신율은 100% 정도로 기계적 물성을 증가시킬 수 있었다.

• 한국식품과학회지
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• 제30권5호
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• pp.1140-1145
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• 1998

대황추출물, 황련추출물, 지르코니움계 은치환무기 이온교환체 등의 항균성 소재를 1% 농도로 함유시킨 LDPE 필름($O_2$, 투과도 : $68{\sim}80\;mL/m^2$ atm hr, $CO_2$ 투과도 : $304{\sim}360\;mL/m^2$ atm hr)을 사용하여 200 g 단위의 딸기에 대해서 환경기체조절포장을 실시하고 $5^{\circ}C$에서 저장하면서 포장내 기체조성, 미생물 증식, 물리화학적 품질변화를 측정하였다. 또한 대황추출물 함유 필름의 포장에 0.5 mm의 핀홀을 2개 낸 세공성 포장, 항균제 무첨가의 대조구 LDPE 밀봉포장, PVC wrap 포장과도 비교하였다. 항균성 LDPE 필름은 포장된 딸기의 총균수, 유산균수, 효모수에서 미생물의 생육을 억제하였고, 밀봉포장될 때 4% 이하의 낮은 $O_2$ 농도 및 $6.3{\sim}9.0%$의 $CO_2$ 농도의 변형기체조성을 유지하였다. 포장필름의 미생물생육억제와 변형기체의 복합적인 상승 효과로 인해 항균성 LDPE 밀봉포장은 대조구 LDPE 포장, 통기성의 PVC wrap 및 세공성 핀홀 포장에 비해 현저하게 낮은 부패율을 보였다. 그리고 이러한 포장은 딸기의 경도 유지에도 긍정적인 효과를 가짐과 아울러 다른 물리화학적 변화에도 부정적인 영향을 주지 않았다.

• 한국재료학회지
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• 제10권9호
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• pp.593-600
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• 2000

본 연구에서는 도핑하지 않은 다이아몬드 박막에서의 전류전도 경로를 체계적으로 규명하고 다이아몬드 박막의 전도기구에 대해 조사하였다. 도핑되지 않은 다결정 다이아몬드 박막에서 두께와 측정방향에 따른 교류 임피던스법에 의해 측정된 저향값이 기존의 표면전도 모델과는 일치하지 안니하였다. 다이아몬드 박막에 구리를 전기도금한 결과 구리는 결정립계에만 불연속적으로 도금되었고 다이아몬드 박막 위에 은을 증착한 후 전지에칭을 한 결과 결정립계가 우선 에칭이 되어 전류가 결정립계를 통하여 흐름을 확인하였다. 또, 리본형 다이아몬드 박막의 표면을 절연층으로 형성시킨 후 박막 내부의 결정립계를 통하여 전류가 흘러 전기도금이 되는 것으로부터 다결정 다이아몬드 박막의 주요 전기전도 경로는 결정립계임을 확인하였다. 높은 전기전도도를 보여주는 다이아몬드 박막은 전도 활성화 에너지가 45meV 정도이었고 dangling bond 밀도는 낮았다. 그러나 산소 열처리나 수소플라즈마처리가 Si passivation 이론과는 반대로 dangling bond 밀도를 증가시키면서 전기전도성을 떨어뜨렸다. 이 결과들과 표면의 탄소화학결합을 연결시켜 높은 전도성을 야기시키는 결합은 H-C-C-H 결합임을 추론하였다.

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.241-245
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• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.13-16
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• 2003

Adhesion of $SrZrO_3$ resistive oxide barrier on Ag sheathed Bi(2223) tapes prepared by the sol-gel and dip-coating method was evaluated with an aid of Taguchi method and Lie($2^1{\times}3^7$) orthogonal arrays to determine the optimal process combination of levels of factors that best satisfy the bigger is better quality characteristic (QC=B). For analyses of results statistical calculations such as average and analysis of variance (ANOVA) were employed to analyze the results for improving the performance qualities of the dip-coated $SrZrO_3$ film. Experimentally, the performance of the films was evaluated in terms of bond strength by varying Sr/Zr moi ratio (A), amount of organic vehicle additives (B), drying temperature (C) and time (D), heat treatment temperature (E) and time (F), respectively. The optimal combination of levels of factors was determined to be $A_3B_2C_3D_2E_1F_3$ having a 90% confidence level.