• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.133-133
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• 1998

In the thin film alloy formation of the transition metals ion-beam-mixing technique forms a metastable structure which cannot be found in the arc-melted metal alloys. Sppecifically it is well known that the studies about the electronic structure of ion-beam-mixed alloys pprovide the useful information in understanding the metastable structures in the metal alloy. We studied the electronic change in the ion-beam-mixed ppt-Ct alloys by XppS and XANES. These analysis tools pprovide us information about the charge transfer in the valence band of intermetallic bonding. The multi-layered films were depposited on the SiO2 substrate by the sequential electron beam evapporation at a ppressure of less than 5$\times$10-7 Torr. These compprise of 4 ppairs of ppt and Cu layers where thicknesses of each layer were varied in order to change the alloy compposition. Ion-beam-mixing pprocess was carried out with 80 keV Ae+ ions with a dose of $1.5\times$ 1016 Ar+/cm2 at room tempperature. The core and valence level energy shift in these system were investigated by x-ray pphotoelectron sppectroscoppy(XppS) pphotoelectrons were excited by monochromatized Al K ａ(1486.6 eV) The ppass energy of the hemisppherical analyzer was 23.5 eV. Core-level binding energies were calibrated with the Fermi level edge. ppt L3-edge and Cu K-edge XANES sppectra were measured with the flourescence mode detector at the 3C1 beam line of the ppLS (ppohang light source). By using the change of White line(WL) area of the each metal sites and the core level shift we can obtain the information about the electrons pparticippating in the intermetallic bonding of the ion-beam-mixed alloys.

• 한국표면공학회지
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• 제39권5호
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• pp.206-209
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• 2006

Indium tin oxide (ITO) films were synthesized on polymer (PES, polyethersulfone) at room temperature by pulsed DC magnetron sputtering. By the control of introducing hydrogen to argon atmosphere, the resistivity of ITO films was obtained at $5.27\;{\times}\;10^{-4}\;{\Omega}{\cdot}cm$ without substrate heating in comparison with $2.65\;{\times}\;10{-3}\;{\Omega}{\cdot}cm$ under hydrogen free condition. ITO film synthesized at Ar condition was changed from amorphous to crystalline. These result from the enhancement of electron temperature in $Ar\;+\;H_2$ plasma, which induces the increase of ionization of target materials and argon. The dominant increase of ions such as In II and O II and neutral Sn I was monitored by optical emission spectroscopy (OES). Thermal energy required for the crystalline film formation is compensated by kinetic energy transfer through ion bombardments to substrate.

• Advances in nano research
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• 제13권1호
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• pp.97-111
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• 2022

In the present article, silica nanoparticles (SNPs) were exploited to improve the tribological and mechanical properties of vinyl ester/glass fiber composites. To the best of our knowledge, there hasn't been any prior study on the wear properties of glass fiber reinforced vinyl ester SiO₂ nanocomposites. The wear resistance is a critical concern in many industries which needs to be managed effectively to reduce high costs. To examine the influence of SNPs on the mechanical properties, seven different weight percentages of vinyl ester/nano-silica composites were initially fabricated. Afterward, based on the tensile testing results of the silica nanocomposites, four wt% of SNPs were selected to fabricate a ternary composite composed of vinyl ester/glass fiber/nano-silica using vacuum-assisted resin transfer molding. At the next stage, the tensile, three-point flexural, Charpy impact, and pin-on-disk wear tests were performed on the ternary composites. The fractured surfaces were analyzed by scanning electron microscopy (SEM) images after conducting previous tests. The most important and interesting result of this study was the development of a nanocomposite that exhibited a 52.2% decrease in the mean coefficient of friction (COF) by augmenting the SNPs, which is beneficial for the fabrication/repair of composite/steel energy pipelines as well as hydraulic and pneumatic pipe systems conveying abrasive materials. Moreover, the weight loss due to wearing the ternary composite containing one wt% of SNPs was significantly reduced by 70%. Such enhanced property of the fabricated nanocomposite may also be an important design factor for marine structures, bridges, and transportation of wind turbine blades.

• 분석과학
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• 제20권5호
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• pp.406-412
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• 2007

분광 광도법을 이용하여 ${\beta}$-CD와 $[Cu(dien)(sub-py)]^{2+}$ 이온 간의 복합체 형성에 관한 연구를 하였다. ${\beta}$-CD와 $Cu^{2+}$ 착물이 복합체를 형성 할 때 ${\gamma}_{max}$은 리간드에 전자 주는기($CH_3$)가 치환 된 경우는 $^2T_2{\rightarrow}^2E$로 한 곳에서, 전자 끄는기(Cl)가 치환된 경우는 $^2T_2{\rightarrow}^2E$와 MLCT에 의하여 두 곳에서 나타났다. 형성상수는 온도가 올라가면 결합에너지의 감소로 작아졌다. 모든 반응은 엔트로피의 감소를 보였으나 큰 발열반응으로 자발적 반응이었다. 치환기 상수(${\sigma}_x$)에 따른 Hammett plot 결과 좋은 직선성(${\gamma}=0.996$)을 보여 형성상수를 정량적으로 설명할 수 있었다.

• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.361-368
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• 2023

In lithium-sulfur (Li-S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid-liquid-solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li-S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge-discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge-discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li-S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.

• 한국환경보건학회지
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• 제28권2호
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• pp.117-129
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• 2002

Concentration of welding fumes and their components is known to be hazardous to welder and adjacent worker. To determine the generation rates of metals in fumes, $CO_2$ flux cored arc welding on stainless steel was performed in well designed fume collection chamber. Variables were different products of flux cored wire(2 domestic products and 4 foreign products) and input energy(low-, optimal- , high input energy). Mass of welding fumes was determined by gravimetric method(NIOSH 0500 method), and 17 metals were analysed by inductively coupled plasm-atomic emission spectroscopy(NIOSH 7300 method). Flux cored wire tube and flux were analysed by scanning electron microscopy to determine their metal composition. 17 metals were classified by their generation rates. Generation rates of iron, manganese, potassium and sodium were all above 50mg/min at optimal input energy level. Generation rates of chromium and amorphous silica were 25~50mg/min. At 1~25mg/min level, nickel, titanium, molybdenum, and aluminum were included. Copper, zinc, calcium, lead, magnesium, lithium, and cobalt were generated below 1 mg/min. Generation rates of metal components in fumes were influenced by input energy, types of flux cored wire. Flux cored wire was consisted of outer shell tube and inner flux. Iron, chromium, and nickel were the major components of outer tube. Flux contained iron, chromium, nickel, potassium, sodium, silica, and manganese. The use of flux cored wire can increase the hazards by increasing the amounts of fumes formed relative to that of solid wire. The reason might be the direct transfer of elements from the flux, since the flux is fine power. Ratio of metals to the fume of flux cored wire was lower than that of solid wire because non-metal components of flux were transferred. Total metal content of fumes in flux cored arc welding was 47.4(24.3~57.2) percent that is much lower than that of solid wire, 75.9 percent. We found that generation rates of iron, manganese, chromium and nickel, all well known to cause work related disease to welder, increased more rapidly with increasing input energy than those of fumes. To reduce worker exposure to fumes and hazardous component at source, further research is needed to develop new welding filler materials that decrease both the amount of fumes and hazardous components.

• 대한환경공학회지
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• 제36권11호
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• pp.753-757
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• 2014

산화전극부 전극은 단순히 전자를 받아 전달할 수 있는 역할 뿐만 아니라 공극이 많아 표면적이 큰 구조로 미생물을 고정화할 수 있는 표면적을 제공할 수 있어야 한다. 미생물의 수가 많을수록 폐수처리 효율과 전류발생을 높일 수 있기 때문이다. 따라서 전극은 미생물연료전지의 효율을 높일 수 있는 중요한 역할을 하는 인자 중의 하나이다. 본 연구는 미생물연료전지에 사용하는 고가의 흑연펠트를 스텐철사 타래(철 수세미)로 대체할 수 있는지 알아보기 위한 것이다. 이 연구에 사용된 가축분뇨는 전처리를 거친 후 유기오염물질(COD)로 500 mg/L로 희석한 것을 이용하였고, 이때 전류 발생은 스텐철사 타래를 적용하였을 때 약 5% 정도 낮았지만 큰 차이가 없는 것으로 나타났다. 유기오염물질(COD)의 감소는 스텐철사 타래를 이용하였을 때 88.3%이었으며, 흑연펠트를 사용하였을 때 82.4%로 스텐철사 타래의 제거율이 더 높게 나타났다. 암모니아성 질소 이온의 경우는 두 경우 모두 반응시간에 따라 농도 변화가 거의 없는 것으로 나타났다. 이 결과 스텐철사 타래를 적용하였을 때 전류발생이나 수처리 측면 모두 효과가 유사하거나 더 좋은 결과를 보였으며, 초기 시스템을 구축하는 비용을 약 1/50 정도로 줄일 수 있는 것으로 예상되어. 흑연펠트 대체제로 적용이 가능할 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.286-286
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• 2016

Hexagonal boron nitride (hBN) is a dielectric insulator with a two-dimensional (2D) layered structure. It is an appealing substrate dielectric for many applications due to its favorable properties, such as a wide band gap energy, chemical inertness and high thermal conductivity[1]. Furthermore, its remarkable mechanical strength renders few-layered hBN a flexible and transparent substrate, ideal for next-generation electronics and optoelectronics in applications. However, the difficulty of preparing high quality large-area hBN films has hindered their widespread use. Generally, large-area hBN layers prepared by chemical vapor deposition (CVD) usually exhibit polycrystalline structures with a typical average grain size of several microns. It has been reported that grain boundaries or dislocations in hBN can degrade its electronic or mechanical properties. Accordingly, large-area single crystalline hBN layers are desired to fully realize the potential advantages of hBN in device applications. In this presentation, we report the growth and transfer of centimeter-sized, nearly single crystal hexagonal boron nitride (hBN) few-layer films using Ni(111) single crystal substrates. The hBN films were grown on Ni(111) substrates using atmospheric pressure chemical vapor deposition (APCVD). The grown films were transferred to arbitrary substrates via an electrochemical delamination technique, and remaining Ni(111) substrates were repeatedly re-used. The crystallinity of the grown films from the atomic to centimeter scale was confirmed based on transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED). Careful study of the growth parameters was also carried out. Moreover, various characterizations confirmed that the grown films exhibited typical characteristics of hexagonal boron nitride layers over the entire area. Our results suggest that hBN can be widely used in various applications where large-area, high quality, and single crystalline 2D insulating layers are required.

• 마이크로전자및패키징학회지
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• 제23권4호
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• pp.87-92
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• 2016

전자소자의 방열모듈에서 두께 방향의 열방출 특성에 대한 중요성이 증가하고 있다. 금속과 금속의 본딩 및 유전체와 금속의 본딩 구조를 갖는 2가지 종류의 2층 층상재료를 제조한 후 두께 방향으로 열확산계수를 측정하였다. 금속(STS439)과 금속(Al6061)으로 이루어진 2층 층상재료에서는 섬광법(LFA)으로 열확산계수를 측정했을 때, 열흐름의 방향을 반대로 변화시켜도 열확산계수의 변화가 없었다. 그런데, 유전체(AlN-Polymer)와 금속(Al6061)의 2층 층상재료에서는 열흐름의 방향을 반대로 인가하였을 때 열확산계수는 17.5% 정도 다르게 나타났다. 유전체와 금속의 단면구조를 갖는 2층 층상재료에서, 금속에서 유전체 방향으로 측정한 열확산계수가 유전체에서 금속 방향으로 측정한 열확산계수에 비해 17.5% 작게 나타난 이유는, 금속내의 전자가 갖고 있던 에너지가 유전체 쪽으로 전달되기 위해서는 계면 주변에서 포논의 에너지 형태로 변환될 때 저항이 생기기 때문이다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권5호
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• pp.285-295
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• 1999

Electroluminescent(EL) devices based on organic materials have been of great interest due to their possible applications for large-area flat-panel displays. They are attractive because of their capability of multi-color emission, and low operation voltage. An approach to realize such device characteristics is to use active layers of lanthanide complexes with their inherent extremely sharp emission bands in stead of commonly known organic dyes. In general, organic molecular compounds show emission due to their $\pi$-$\pi*$ transitions resulting in luminescence bandwidths of about 80 to 100nm. Spin statistic estimations lead to an internal quantum efficiency of dye-based EL devices limited to 25%. On the contrary, the fluorescence of lanthanide complexes is based on an intramolecular energy transfer from the triplet of the organic ligand to the 4f energy states of the ion. Therefore, theoretical internal quantum efficiency is principally not limited. In this study, Powders of TPD, $Eu(TTA)_3(phen) and AlQ_3$ in a boat were subsequently heated to their sublimation temperatures to obtain the growth rates of 0.2~0.3nm/s. Organic electrolumnescent devices(OELD) with a structure of $glass substrate/ITO/Eu(TTA)_3(phen)/AI, glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AI and glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AIQ_3AI$ structures were fabricated by vacuum evaporation method, where aromatic diamine(TPD) was used as a hole transporting material, $Eu(TTA)_3(phen)$ as an emitting material, and Tris(8-hydroxyquinoline)Aluminum$(AlQ_3)$ as an electron transporting layer. Electroluminescent(EL) and current density-voltage(J-V) characteristics of these OELDs with various thickness of $Eu(TTA)_3(phen)$ layer were investigated. The triple-layer structure devices show the red EL spectrum at the wavelength of 613nm, which is almost the same as the photoluminescent(PL) spectrum of $Eu(TTA)_3(phen)$.It was found from the J-V characteristics of these devices that the current density is not dependent on the applied field, but on the electric field.