• Journal of the Korean Ceramic Society
• /
• v.39 no.6
• /
• pp.582-588
• /
• 2002

IrO$_2$-RuO$_2$ films were deposited on plasma sprayed TiO$_2$ buffer layer above Ti metal by sol-gel and dip-coating method. Organic vehicle (ethyl cellulose and $\alpha$-terpineol) and glass frit were added to improve adherence of the coatings. Taguchi method and L$_{18}$ (2$^1$$\times$3$^{7}$ ) orthogonal arrays were evalvated in terms of current density to determine the optimal combination of levels of factors that best satisfy the bigger is better quality characteristic. The observed conditions were as fellows: ethyl cellulose (100 cp), drying temperature and time (17$0^{\circ}C$,20 min), heat treatment temperature and time (75$0^{\circ}C$,10 min), the weight ratio of IrO$_2$-RuO/powders to glass frit (99:5), final heat treatment time (120 min) and flow rate of air (5 sccm), respectively. ANOVA analysis suggested that the influence of the factors within $\alpha$= 0.1 was significant with a 90% confidence level.

• Korean Journal of Optics and Photonics
• /
• v.21 no.1
• /
• pp.33-37
• /
• 2010

We performed time-domain terahertz (THz) spectroscopy to determine optical constants of highly conductive carbon nanotube (CNT) films. The CNT films have been fabricated on a flexible plastic substrate by using spin-coating or vacuum filtration. We found that the transmission of THz waves can be controlled by manipulating the thickness of the films and by post-treatments. From amplitude and phase information of the transmitted THz waves, we obtain optical constants such as refractive indices and dielectric constants of the CNT films. The frequency dependent dielectric constants show good metallic behaviors, relevant to the Drude free electron models with high plasma frequencies. It is also found that the dielectric constants are higher for the acid-treated films. Finally, the frequency dependent dielectric constants which are free from substrate effects have been demonstrated by using CNT films deposited on cellulose membranes.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.163-163
• /
• 2010

중적외선 영역 ($3{\sim}5\;{\mu}m$)은 공기 중에 존재하는 이산화탄소나 수증기에 의해 흡수가 일어나지 않기 때문에 군사적으로 중요한 파장 영역이며, 야간에 적을 탐지하는데 응용되고 있다. InSb는 77 K에서 중적외선 파장 흡수에 적합한 밴드갭 에너지 (0.228 eV)를 갖고 있으며, 다른 화합물 반도체와 달리 전하 수송자 이동도 (전자: $10^6\;cm^2/Vs$, 정공: $10^4\;cm^2/Vs$)가 매우 빠르기 때문에 적외선 화상 감지기 재료로 매우 적합하다. 또한 현재 중적외선 영역대에서 널리 사용되는 HgCdTe (MCT)와 대등한 소자 성능을 나타냄과 동시에 낮은 기판 가격, 소자의 제작 용이성 때문에 MCT를 대체할 물질로 주목 받고 있다. 하지만, 기판과 절연막의 계면에 존재하는 결함 때문에 에너지 밴드갭 내에 에너지 준위를 형성하여 높은 누설 전류 특성을 보인다. 따라서 InSb 적외선 소자의 구현을 위하여 고품질의 절연막의 연구가 필수적이라고 할 수 있겠다. 절연막의 특성을 알아보기 위해, n형 InSb 기판에 플라즈마 화학 기상 증착법 (PECVD)을 이용하여 $SiO_2$, $Si_3N_4$를 증착하였으며, 증착 온도를 $120^{\circ}C$에서 $240^{\circ}C$까지 $40^{\circ}C$ 간격으로 변화하여 증착온도가 미치는 영향에 대하여 알아보았다. 절연막과 기판의 계면 특성을 분석하기 위하여 77 K에서 커패시턴스-전압 (C-V) 분석을 하였으며, 계면 트랩 밀도는 Terman method를 이용하여 계산하였다 [1]. $Si_3N_4$를 증착하였을 경우, $120{\sim}240^{\circ}C$의 증착 온도에서 $2.4{\sim}4.9{\times}10^{12}\;cm^{-2}eV^{-1}$의 계면 트랩 밀도를 가졌으며, 증착 온도가 증가할수록 계면 트랩 밀도가 증가하는 경향을 보였다. 또한 모든 증착 온도에서 flat band voltage가 음의 전압으로 이동하였다. $SiO_2$의 경우 $120{\sim}200^{\circ}C$의 증착온도에서 $7.1{\sim}7.3{\times}10^{11}\;cm^{-2}eV^{-1}$의 계면 트랩 밀도 값을 보였으나, $240^{\circ}C$ 이상에서 계면 트랩밀도가 $12{\times}10^{11}\;cm^{-2}eV^{-1}$로 크게 증가하였다. $SiO_2$ 절연막을 사용함으로써, $Si_3N_4$ 대비 약 25% 정도 낮은 계면 트랩 밀도를 얻을 수 있었으며, 모든 증착 온도에서 양의 전압으로 flat band voltage가 이동하였다. 두 절연막에 대한 계면 트랩의 원인을 분석하기 위하여 XPS 측정을 진행하였으며, 깊이에 따른 조성 분석을 하였다. 본 실험에서 최적화된 $SiO_2$ 절연막을 이용하여 InSb 소자의 pn 접합 연구를 진행하였다. Be+ 이온 주입을 진행하고, 급속열처리(RTA) 공정을 통하여 p층을 형성하였다. -0.1 V에서 16 nA의 누설 전류 값을 보였으며, $2.6{\times}10^3\;{\Omega}\;cm^2$의 RoA (zero bias resistance area)를 얻을 수 있었다.

• Journal of Powder Materials
• /
• v.24 no.6
• /
• pp.437-443
• /
• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2018.06a
• /
• pp.124-124
• /
• 2018

Polydopamine은 수중 접착력, 친환경 접착제, nanoparticle absorption 등 다양한 특성으로 많이 연구되고 있는 소재이다. 본 연구에서는 dopamine을 이용하여 수중 금속을 흡착시키는 thin film을 제작하였다. 종래의 Polydopamine coating 방법으로 wet coating 이 사용되고 있다. 하지만 wet 방식의 경우 시간이 오래 걸릴 뿐만 아니라 in-line, roll to roll 방식을 적용하는 것이 어렵기 때문에 생산적이지 않다. 이에 본 연구에서는 Atmospheric Pressure Plasma(APP)를 이용 하여 Polydopamine-like film을 coating 하였다. APP의 경우 vacuum system, solution tank가 필요 없고 in-line, roll to roll 방식을 적용 할 수 있기 때문에 더 경제적이고 생산적인 공정이다. 또한 기존의 Plasma polymerization 방법은 Plasma energy가 높기 때문에 source의 분자구조가 바뀌거나 atom 단위로 분해된다. source의 분자구조가 바뀌는 "Atomic polymerization", Neiswender-Rosskamp Mechanism이 적용되면 wet 방식 coating한 film과는 다른 특성을 갖게 된다. 하지만 APP polymerization은 Plasma energy가 vacuum plasma 보다 매우 낮기 때문에 stile polymerization mechanism을 구현 하는데 적합 하다. stile polymerization mechanism은 Plasma 내부에서 polymer source를 분해 성장 시켜서 Polymer film 얻는 것이 아닌 source의 분자구조가 깨지지 않으면서 polymer growing 시키는 방법이다. dopamine source의 분자구조를 최대한 유지하려고 하는 이유는 metal absorption과 같은 특성이 dopamine chemical structure에 영향을 받기 때문이다. 많은 논문들에서 dopamine의 catechol group이 metal absorption, adhesion force에 영향을 주는 주요 인자라고 주장하고 있기 때문이다. 그래서 본 논문에서는 Dopamine source의 형태를 보존하면서 Polymerization 하는 방법으로 APP process를 사용 하여 낮은 전압에서 Polydopamine-like film을 제작 하였다. APP system 의 Plasma 방전부 에 Dopamine source를 유입하기 위하여 본 논문에서는 Piezo Spray 방식을 사용 하였다. Dopamine을 evaporator 하는 것이 어렵고 chemical composition이 유사한 monomer를 사용해서 Plasma Polymerization으로 Dopamine 분자 구조를 재현하는 것도 어렵다. 그래서 본 연구에서는 Dopamine을 water에 immerse 하고 Dopamine solution을 mist 상태로 만들어서 Plasma discharge area에 유입하였다. 이러한 방법으로 만들어진 film은 Polydopamine film은 아니지만 Polydopamine film과 유사한 Chemical composition, chemical structure, metal absorption을 갖는 것을 FT-IR, SEM, XPS을 이용 하여 확인 하였다. Dopamine source의 보존에 대하여 명확하게 확인하기 위하여 FT-IR을 측정 하였다. 전압에 따른 Benzene ring, hydroxyl group의 비율을 확인 하였다. 낮은 전압으로 coating 된 Polydopamine-like film 일수록 hydroxyl group peak($3400{\sim}3000cm^{-1}$)과 비교하여 Benzene ring peak($1600{\sim}1580cm^{-1}$ and $1510{\sim}500cm^{-1}$)이 흡수를 더 많이 하는 것을 확인 할 수 있다. 이것은 Benzene ring이 파괴되지 않고 보존되는 것을 보여준다. Dopamine에서 Benzene ring은 absorption main factor인 catechol에 있는 chemical structure이다. 즉 Benzene ring peak이 높을수록 Catechol이 잘 보존 되었다는 의미 이다. Catechol의 보존은 absorption main factor가 보존 된다는 의미 이다. 이러한 Polydopamine-like film으로 As, Cr, Mg, Cu 200ppm solution에 대한 filtration 능력을 확인 하였다. As, Cr, Cu, Mg 의 제거율이 각각 약25%, 35%, 45%, 65%인 것을 확인 하였다. 이 수치는 시중에 판매되는 제품들과 비교했을 때 300%~500% 향상된 수치 이다.

• Korean Chemical Engineering Research
• /
• v.43 no.1
• /
• pp.27-32
• /
• 2005

We propose an effective and environmentally friendly dry stripping method using a supercritical carbon dioxide ($SCCO_2$) system modified by a single and multiple cosolvents to remove ion-implanted photoresist and residue from a wafer surface at three different temperatures (97, 148, $200^{\circ}C$) and pressures (200, 300, 400 bar). After high dose of ion implantation the photoresist was not easily removed by using pure $SCCO_2$, but swollen. The $SCCO_2$ system modified by single cosolvents and multiple cosolvents mixed with aprotic solvents could not effectively remove the heavy organics, but swell them. However, the $SCCO_2$ system modified with multiple cosolvent (5%, v/v) composed of DMSO and DIW showed high removal efficiency for ion-implanted photoresists at $97^{\circ}C$ and 200 bar for 30 min (about 80%). In this study it has been shown that the dry stripping method using $SCCO_2$ system modified with multiple cosolvents could replace either plasma ashing or acid and solvent wet bench method and dramatically reduce accompanied chemical usage and disposal.

• Korean Chemical Engineering Research
• /
• v.46 no.6
• /
• pp.1100-1106
• /
• 2008

In this study, we presented rapid and simple fabrication method of functionalized surface on various substrates as a universal platform for the selective immobilization of cells. The functionalized surface was achieved by using deposition of polyelectrolyte such as poly(allyamine hydrochloride) (PAH), poly(diallyldimethyl ammonium chloride) (PDAC), poly(4-ammonium styrene sulfonic acid) (PSS), poly(acrylic acid) (PAA) and fabrication of poly(ethylene glycol) (PEG) microstructure through micro-molding in capillaries (MIMIC) technique on each glass, poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(dimethyl siloxane) (PDMS) substrate. The polyelectrolyte multilayer provides adhesion force via strong electrostatic attraction between cell and surface. On the other hand, PEG microstructures also lead to prevent non-specific binding of cells because of physical and biological barrier. The characteristic of each modified surface was examined by using static contact angle measurement. The modified surface onto several substrates provides appropriate environment for cellular adhesion, which is essential technology for cell patterning with high yield and viability in the micropatterning technology. The proposed method is reproducible, convenient and rapid. In addition, the fabrication process is environmentally friendly process due to the no use of harsh solvent. It can be applied to the fabrication of biological sensor, biomolecules patterning, microelectronics devices, screening system, and study of cell-surface interaction.

• Membrane Journal
• /
• v.6 no.3
• /
• pp.173-181
• /
• 1996

Common volatile organic compounds(VOCs) such as toluene and methanol were removed successfully from N$_{2}$ using a novel silicone-coated hollow fiber membrane module. This novel membrane is a thin film composite(TFC) and was highly efficient in removing VOCs selectively from a N$_{2}$ stream. This membrane had some innate advantages over other silicone-based membrane in that the selective barrier was ultrathin(~1 $\mu$m) and the porosity of the polypropylene substrate was high which leads to a low permeation resistance. The substram was very strongly bonded to the coating layer by plasma polymerization and can withstand a very high pressure. A small hollow fiber module having a length of 25cm and 50 fibers could remove 96~99% of toluene as well as methanol vapors when the feed flow rate was up to 60cc/min. The percent removal of VOCs were even higher when the feed inlet concentration was higher. This process is especially suitable for treating streams having a low flow rate and high VOCs concentration. The permeances of VOCs through this membrane was in the range of $4~30 \times 10^{-9}gmol/sec \cdot cm^{2}\cdot cmHg$ for both toluene and methanol, and nitrogen permeance was between $3~9 \times 10^{-10}gmol/sec \cdot cm^{2} \cdot cmHg$. High separation factor between 10~55 for toluene/N$_{2}$ and 15~125 for methanol/N$_{2}$ were obtained depending on the feed flow rate ranges and feed VOCs concentration levels.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.15 no.3
• /
• pp.191-197
• /
• 2017

The Korea Atomic Energy Research Institute (KAERI) has developed a safeguards technology for pyroprocessing based on the Safeguards-By-Design (SBD) concept. KAERI took part in a Member-State Support Program (MSSP) to establish a pyroprocessing safeguards approach. A Reference Engineering-scale Pyroprocessing Facility (REPF) concept was designed on which KAERI developed its safeguards system. Recently the REPF is being upgraded to the REPF+, a scaled-up facility. For assessment of the nuclear-material accountancy (NMA) system, KAERI has developed a simulation program named Pyroprocessing Material Flow and MUF Uncertainty Simulation (PYMUS). The PYMUS is currently being upgraded to include a Near-Real-Time Accountancy (NRTA) statistical analysis function. The Advanced Spent Fuel Conditioning Process Safeguards Neutron Counter (ASNC) has been updated as Non-Destructive Assay (NDA) equipment for input-material accountancy, and a Hybrid Induced-fission-based Pu-Accounting Instrument (HIPAI) has been developed for the NMA of uranium/transuranic (U/TRU) ingots. Currently, performance testing of Compton-suppressed Gamma-ray measurement, Laser-Induced Breakdown Spectroscopy (LIBS), and homogenization sampling are underway. These efforts will provide an essential basis for the realization of an advanced nuclear-fuel cycle in the ROK.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.2
• /
• pp.65-69
• /
• 2014

Crystallographic phases of Plasma electrolytic oxidized Al alloy, A1100, A5052, A6061, A6063, A7075, were investigated. Two types of electrolyte $Na_2Si_2O_3$ and Na2P2O7 were also compared. Bipolar pulse, $2000{\mu}sec$ with $400{\mu}sec+420V$ impulse and $300{\mu}sec$ - impulse were applied for 20 min. ${\alpha}-alumina$, ${\gamma}-alumina$, ${\eta}-alumina$, $Al_{4.95}Si_{1.05}O_{9.52}$, and $(Al_{0.9}Cr_{0.1})_2O_3$ were mainly observed. Si, component of electrolyte, were moved into the PEO layer by bipolar pulse. Glassy phase was also observed at the surface of $Na_2Si_2O_3$ electrolyte treated PEO layer, and increased with the Mg content of Al alloy. It is concluded that at first glassy phase was formed by the micro plasma, and the high temperature of plasma turns glassy phase to several crystalline phases. And we could expect that many other crystalline phase could be formed by PEO process.