• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.339-344
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• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.35.1-35.1
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• 2011

New photovoltaic (PV) materials and manufacturing approaches are needed for meeting the demand for lower-cost solar cells. The prototypal thin-film photovoltaic absorbers (CdTe and $Cu(In,Ga)Se_2$) can achieve solar conversion efficiencies of up to 20% and are now commercially available, but the presence of toxic (Cd,Se) and expensive elemental components (In, Te) is a real issue as the demand for photovoltaics rapidly increases. To overcome these limitations, there has been substantial interest in developing viable alternative materials, such as $Cu_2ZnSnS_4$ (CZTS) is an emerging solar absorber that is structurally similar to CIGS, but contains only earth abundant, non-toxic elements and has a near optimal direct band gap energy of 1.4~1.6 ev and a large absorption coefficient of ${\sim}10^4\;cm^{-1}$. The CZTS absorber layers are grown and investigated by various fabrication methods, such as thermal evaporation, e-beam evaporation with a post sulfurization, sputtering, non-vacuum sol-gel, pulsed laser, spray-pyrolysis method and electrodeposition technique. In the present work, we report an alternative method for large area deposition of CZTS thin films that is potentially high throughput and inexpensive when used to produce monolithically integrated solar panel modules. Specifically, we have developed an aqueous chemical approach based on chemical bath deposition (CBD) with a subsequent sulfurization heat treatment. Samples produced by our method were analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, absorbance and photoluminescence. The results show that this inexpensive and relatively benign process produces thin films of CZTS exhibiting uniform composition, kesterite crystal structure, and good optical properties. A preliminary solar cell device was fabricated to demonstrate rectifying and photovoltaic behavior.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.25.1-25.1
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• 2011

Over the past few decades, metallic nanoparticles (NPs) have been of great interest due to their unique mesoscopic properties which distinguish them from those of bulk metals; such as lowered melting points, greater versatility that allows for more ease of processability, and tunable optical and mechanical properties. Due to these unique properties, potential opportunities are seen for applications that incorporate nanomaterials into optical and electronic devices. Specifically, the development of metallic NPs has gained significant interest within the electronics field and technological community as a whole. In this study, gold (Au) pads for surface finish in electronic package were developed by inkjet printing of Au NPs. The microstructures of inkjet-printed Au film were investigated by various thermal treatment conditions. The film showed the grain growth as well as bonding between NPs. The film became denser with pore elimination when NPs were sintered under gas flows of $N_2$-bubbled through formic acid ($FA/N_2$) and $N_2$, which resulted in improvement of electrical conductance. The resistivity of film was 4.79 ${\mu}{\Omega}$-cm, about twice of bulk value. From organic anlayses of FTIR, Raman spectroscopy, and TGA, the amount of organic residue in the film was 0.43% which meant considerable removal of the solvent or organic capping molecules. The solder ball shear test was adopted for solderability and shear strength value was 820 gf (1 gf=9.81 mN) on average. This shear strength is good enough to substitute the inkjet-printed Au nanoparticulate film for electroplating in electronic package.

• 한국재료학회지
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• 제19권10호
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• pp.544-549
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• 2009

Activated carbon (AC) with very large surface area has high capacitance per weight. However, such activation methods tend to suffer from low yields, below 50%, and are low in electrode density and capacitance per volume. Carbon NanoFibers (CNFs) had high surface area polarizability, high electrical conductivity and chemical stability, as well as extremely high mechanical strength and modulus, which make them an important material for electrochemical capacitors. The electrochemical properties of immobilized CNF electrodes were studied for use as in electrical double layer capacitor (EDLC) applications. Immobilized CNFs on Ni foam grown by thermal chemical vapor deposition (CVD) were successfully fabricated. CNFs had a uniform diameter range from 50 to 60 nm. Surface area was 56 m$^2$/g. CNF electrodes were compared with AC and multi wall carbon nanotube (MWNT) electrodes. The electrochemical performance of the various electrodes was examined with aqueous electrolyte of 2M KOH. Equivalent series resistance (ESR) of the CNF electrodes was lower than that of AC and MWNT electrodes. The specific capacitance of 47.5 F/g of the CNF electrodes was achieved with discharge current density of 1 mA/cm$^2$.

• 한국항공우주학회지
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• 제36권9호
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• pp.916-922
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• 2008

우주용 구조물에 사용되는 재료는 치수 안정성을 위해서 열팽창계수를 최소화하도록 설계, 제작되어야 한다. 이를 위하여 우주용 재료 시편의 정밀한 열팽창계수를 측정하여, 그 재료의 열 특성에 대한 정확한 데이터를 확보할 필요가 있다. 그리고 시편뿐만 아니라 실제 사용될 구조물의 열 변형을 우주 환경에서 직접 측정할 필요가 있다. 따라서 본 연구에서는 고진공에서 정밀한 변위 측정을 위하여 변위 측정 간섭계와 항우연의 보조 챔버를 활용한 열팽창계수 측정 시스템을 설계하였다. 또한 본 측정 시스템은 길이 500mm 정도의 긴 구조물의 열 변형

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.230-230
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• 2013

In amorphous or microcrystalline thin-film silicon solar cells, p-i-n structure is used instead of p/n junction structure as in wafer-based Si solar cells. Hence, these p-i-n structured solar cells inevitably consist of many interfaces and the cell efficiency critically depends on the effective control of these interfaces. In this study, in-situ plasma treatment process of the interfaces was developed to improve the efficiency of a-Si:H solar cell. The p-i-n cell was deposited using a single-chamber VHF-PECVD system, which was driven by a pulsed-RF generator at 80 MHz. In order to solve the cross-contamination problem of p-i layer, high RF power was applied without supplying SiH4 gas after p-layer deposition, which effectively cleaned B contamination inside chamber wall from p-layer deposition. In addition to the p-i interface control, various interface control techniques such as thin layer of TiO2 deposition to prevent H2 plasma reduction of FTO layer, multiple applications of thin i-layer deposition and H2 plasma treatment, H2 plasma treatment of i-layer prior to n-layer deposition, etc. were developed. In order to reduce the reflection at the air-glass interface, anti-reflective SiO2 coating was also adopted. The initial solar cell efficiency over 11% could be achieved for test cell area of 0.2 $cm^2$.

• 청정기술
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• 제19권3호
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• pp.272-278
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• 2013

EPDM 고무는 여러 가지 용도에 많이 사용되고 있는 소재이다. 화력발전소의 소각로에서 부산물로 발생하는 버텀애쉬(bottom ash)는 플라이애쉬(fly ash)와는 달리 재활용이 거의 되지 않고 있는데, 본 연구에서는 버텀애쉬 및 탈크를 포함하는 EPDM 복합소재를 roll-mill을 이용하여 제조한 후, 기계적, 열적, 전기적 및 경화 특성 등을 분석하였다. 또한 주사전자현미경(scanning electron microscopy, SEM)을 이용하여 복합재료의 모폴로지를 관찰하였다. 일부의 버텀애쉬는 계면활성제를 이용하여 개질한 후 EPDM 복합재료를 제조하여 개질의 효과를 조사하였다. 결과로 개질된 버텀애쉬 및 탈크를 포함하는 EPDM 복합재료는 우수한 인장 강도 및 인장 탄성률을 나타내었다. EPDM 복합재료의 체적 저항은 $10^{14}{\Omega}cm$ 이상으로 전기 절연체로서 저항 임계치를 만족하였고, 열적 물성 결과 버텀애쉬 및 탈크가 EPDM의 열적 안정성을 높여 주는 것으로 확인되었다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.1038-1041
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• 2003

In the paper, we investigated silicon surface microstructures formed by reactive ion etching in hollow cathode system. Wet anisotropic chemical etching technique use to form random pyramidal structure on <100> silicon wafers usually is not effective in texturing of low-cost multicrystalline silicon wafers because of random orientation nature, but High density hollow cathode plasma system illustrates high deposition rate, better film crystal structure, improved etching characteristics. The etched silicon surface is covered by columnar microstructures with diameters form 50 to 100nm and depth of about 500nm. We used $SF_{6}$ and $O_{2}$ gases in HCP dry etch process. This paper demonstrates very high plasma density of $2{\times}10^{12}$ $cm^{-3}$ at a discharge current of 20 mA. Silicon etch rate of 1.3 ${\mu}s/min$. was achieved with $SF_{6}/O_{2}$ plasma conditions of total gas pressure=50 mTorr, gas flow rate=40 sccm, and rf power=200 W. Our experimental results can be used in various display systems such as thin film growth and etching for TFT-LCDs, emitter tip formations for FEDs, and bright plasma discharge for PDP applications. In this paper we directed our study to the silicon etching properties such as high etching rate, large area uniformity, low power with the high density plasma.

• 대한공간정보학회지
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• 제20권2호
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• pp.109-117
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• 2012

최근 복합적 대형 재난이 빈번히 발생하면서 전지구적인 재해 재난 모니터링을 위해 인공위성 센서, 항공/지상 LiDAR 등 다양한 관측센서들이 활용되고 있다. 특히, 전지구를 주기적 반복적으로 관측하며 cm급 고해상도 공간 영상정보를 제공하는 상업 위성은 국가적 재해 재난 발생에 대한 전조 모니터링에서부터 신속한 복구 등 재해 재난업무에 그 활용범위가 확대되고 있다. 그러나, 기존의 독자적 위성운용 시스템만으로는 광역적이고 준실시간적 대응을 요하는 재해 재난 상황 대응에는 한계가 있으므로, 다중 센서가 탑재된 탑재체 운용, 여러 대의 탑재체를 연동하여 적시에 위성영상을 확보하기 위한 긴밀한 국제적 협력체계가 필요하다. 본 논문에서는 지난 2011년 발생했던 국내 폭설 및 집중호우 재난 대응을 위해 국립방재연구원과 국제재난기구인 International Charter와의 협업을 통하여 신속한 위성영상 수급과 자료처리, GIS 분석, 지도화(mapping)함으로써 적시적으로 의사결정지원이 가능한 재난관리 체계를 제시하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.370.1-370.1
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• 2014

Giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), and magnetic random-access memory (MRAM) are currently active areas of research. Magnetite, Fe3O4, is predicted to possess as half-metallic nature, ~100% spin polarization (P), and has a high Curie temperature (TC~850 K). On the other hand, Spinel ferrite CoFe2O4 has been widely studies for various applications such as magnetorestrictive sensors, microwave devices, biomolecular drug delivery, and electronic devices, due to its large magnetocrystalline anisotropy, chemical stability, and unique nonlinear spin-wave properties. Here we have investigated the magneto-transport properties of epitaxial CoxFe3-xO4 thin films. The epitaxial CoxFe3-xO4 (x=0; 0.4; 0.6; 1) thin films were successfully grown on MgO (100) substrate by molecular beam epitaxy (MBE). The quality of the films during growth was monitored by reflection high electron energy diffraction (RHEED). From temperature dependent resistivity measurement, we observed that the Werwey transition (1st order metal-insulator transition) temperature increased with increasing x and the resistivity of film also increased with the increasing x up to $1.6{\Omega}-cm$ for x=1. The magnetoresistance (MR) was measured with magnetic field applied perpendicular to film. A negative transverse MR was disappeared with x=0.6 and 1. Anomalous Hall data will be discussed.