• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.310-310
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• 2014

ZnO박막은 넓은 밴드갭 (3.37 eV), 높은 여기 결합 에너지 (60 meV)를 가지는 육방정계 우르자이트(hexagonal wurtzite) 결정구조를 가지는 II-VI족 화합물 반도체로, 가시광선 영역에서의 높은 광학적 투과도 특성과 자외선 파장에서 발광이 가능한 장점을 가진다. 최근, ZnO박막 성장 기술이 상당히 발전하였지만, 아직까지도 p-형 ZnO박막 성장 기술은 충분히 발전하지 못하여 ZnO의 동종접합 LED는 아직 상용화되지 않고 있는 실정이다. 따라서, 많은 연구 그룹에서 p-GaN, p-SiC, p-diamond, p-Si 등과 같은 p-type 물질 위에 n-type ZnO를 성장시킨 이종접합 다이오드가 연구되고 있다. 특히, p-GaN의 경우 ZnO와의 격자 불일치 정도가 1.8 % 정도로 작다는 장점이 있어 많은 연구가 이루어 지고 있다. 일반적으로 c-축을 기반으로 한 극성ZnO 발광다이오드에서는 자발 분극과 압전 분극 현상에 의해 밴드 휨 현상이 발생하고, 이로 인해 전자와 정공의 공간적 분리가 발생하게 되어 발광 재결합 효율이 제한되고 있다는 문제가 발생한다. 따라서, 본 연구에서는 극성 (0001) 및 비극성 (10-10) n-ZnO/p-GaN 발광다이오드의 성장 및 발광 소자의 전기 및 광학적 특성에 대한 비교 연구를 진행하였다. 금속유기 화학증착법을 이용하여 c-면과 m-면 위에 각각 극성 (0001) 및 반극성 (11-22) GaN박막을 $2.0{\mu}m$ 성장시킨 후 Mg 도핑을 한 p-GaN을 $0.4{\mu}m$ 성장시켜 각각 극성 (0001) 및 반극성 (11-22) p-GaN템플릿을 준비하였다. 이후, N2분위기 $700^{\circ}C$에서 3분동안 열처리를 통하여 Mg 도펀트를 활성화시킨 후 원자층 증착법을 이용하여 동시에 극성 및 반극성 p-GaN의 위에 n-ZnO를 $0.11{\mu}m$ 성장시켜 이종접합구조의 발광소자를 형성하였다. 이때, 극성 (0001) p-GaN 위에는 극성의 n-ZnO 박막이 성장되는 반면, 반극성 (11-22) p-GaN 위에는 비극성 (10-10) n-ZnO 박막이 성장됨을 HR-XRD로 확인하였다. 극성 (0001) n-ZnO/p-GaN이종접합 발광다이오드의 전계 발광 스펙트럼에서는 430 nm 와 550 nm의 두 피크가 동시에 관찰되었다. 430 nm 대역의 파장은 p-GaN의 깊은 준위에서 발광하는 것으로 판단되며, 550 nm 피크 영역은 ZnO의 깊은 준위에서 발광되는 것으로 판단된다. 특히, 10 mA 이하의 저전류 주입시 550 nm의 피크는 430 nm 영역보다 더 큰 발광세기를 나타내고 있다. 하지만, 10 mA 이상의 전류주입 하에서는 550 nm의 영역보다 430 nm의 발광세기가 더욱 증가하는 것을 확인할 수 있었다. 이것은 ZnO의 밴드갭이 3.37 eV로 GaN의 밴드갭인 3.4 eV다 작기 때문에 우선적으로 ZnO의 깊은 준위에서 발광하는 550 nm가 더욱 우세하지만, 지속적으로 전류주입 증가에 따른 캐리어 증가시 n-ZnO에서 p-GaN로 전자가 넘어가며 p-GaN의 깊은 준위인 430 nm에서의 피크가 우세해지는 것으로 판단된다. 반면에, 비극성 (10-10) n-ZnO/반극성 (11-22) p-GaN 구조의 이종접합 발광다이오드로 전계 발광 스펙트럼에서는 극성 (0001) n-ZnO/p-GaN에 비하여 매우 낮은 전계 발광 세기를 나타내고 있다. 이는, 극성 n-ZnO/p-GaN에 비하여 비극성 n-ZnO/반극성 p-GaN의 결정성이 상대적으로 낮기 때문으로 판단된다. 또한, 20 mA 영역에서도 510 nm의 깊은 준위와 430 nm의 발광이 관찰되었다. 동일한 20 mA하에서 두 피크의 발광세기를 비교하면 430 nm의 영역은 극성 n-ZnO/p-GaN에 비하여 매우 낮은 값을 나타내고 있다. 이는 반극성 (11-22) p-GaN의 경우 극성 (0001) p-GaN에 비하여 우수한 p-형 특성에 기인한 것으로 판단된다.

• Korean Chemical Engineering Research
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• v.45 no.2
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• pp.178-182
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• 2007

Non-aqueous supercapacitors by using activated C and $LiMn_2O_4$ as an active material in a positive electrode were prepared and characterized. From the cyclic voltammetry and AC impedance analysis, the capacitive effect by electric double layer of activated carbon and the faradic effect by intercalation/deintercalation of $Li^+$ ion were observed. Increasing the ratio of $LiMn_2O_4$, specific capacitances and energy densities of supercapacitor were increased. At the ratio of 0.86:0.14 ($LiMn_2O_4:C$), the maximum specific capacitance of 17.51 Wh/L and energy density of 23.83 F/cc were obtained, which were more than twice of those for a conventional electric double layer capacitor. Even after 1,000 charge/discharge cycle, the supercapacitor by using the electrode containing 14% of activated carbon and 86% of $LiMn_2O_4$ showed 60% better specific capacitance and energy density than that by using the electrode containing 100% activated carbon.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.232-239
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• 2008

The dental orthodontic mini-screw requires good mechanical properties and high corrosion resistance for implantation in the bone. The purpose of this study was to investigate the electrochemical characteristics of TiN and ZrN coated orthodontic mini-screws, mini-screws were used for experiment. Ion plating was carried out for mini-screw using Ti and Zr coating materials with nitrogen gas. Ion plated surface of each specimen w as o bserved with f ield emission scanning e lectron microscopy ( FE-SEM), e nergy dispersive x-ray spectroscopy (EDX), and electrochemical tester. The surface of TiN and ZrN coated mini-screw were more smooth than that of other kinds of non-coated mini-screw due to dercrease of machined defects. The corrosion current density of the TiN and ZrN coated mini-screw decreased compared to non-coated sample. The corrosion potential of TiN and ZrN coated mini-screw were higher than that of non-coated mini-screw in 0.9% NaCl solution. The pitting corrosion resistance increased in the order of ZrN coated, TiN coated and non-coated wire. Pitting potential of ZrN coated mini-screw was the highest in the other specimens.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.226-231
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• 2008

Titanium and its alloy have been widely used in dental implant and orthopedic prostheses. Electrochemical characteristics of dental implant in the various simulated body fluids have been researched by using electrochemical methods. Ti-6Al-4V alloy implant was used for corrosion test in 0.9% NaCl, artificial saliva and simulated body fluids. The surface morphology was observed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The electrochemical stability was investigated using potentiosat (EG&G Co, 263A). The corrosion surface was observed using scanning electron microscopy (SEM). From the results of potentiodynamic test in various solution, the current density of implant tested in SBF and AS solution was lower than that of implant tested in 0.9% NaCl solution. From the results of passive film stability test, the variation of current density at constant 250 mV showed the consistent with time in the case of implant tested in SBF and AS solution, whereas, the current density at constant 250mV in the case of implant tested in 0.9% NaCl solution showed higher compared to SBF and AS solution as time increased. From the results of cyclic potentiodynamic test, the pitting potential and |$E_{pit}\;-\;E_{corr}$| of implant tested in SBF and AS solution were higher than those of implant tested in 0.9% NaCl solution.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.3
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• pp.115-121
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• 2008

Microstructure of glass-ceramics obtained by heat treating silicate glass containing 50 wt% electric arc furnace dust (EAF dust) and nucleation agents were observed. The crystallization temperature, $T_c$ of glassy specimen measured around $850^{\circ}C$ from different thermal analysis, so the heat treatment condition to obtain glass-ceramic specimen was selected as $950^{\circ}C/15 hr$. The nucleation agent, $TiO_2$ showed the superior effect on enhancing franklinite crystal growth which has stronger mechanical properties and more durable chemical resistance than willemite phase. Some specimens containing $TiO_2$ had the augite crystal phase and increasing $TiO_2$ amount decreased a fraction of willemite and increased a franklinite. Especially, the specimen with 5 wt% $TiO_2$ showed no willemite crystal phase and $1{\sim}2\;{\mu}m$ franklinite crystals dispersed uniformly in glassy matrix. Also, the specimens containing 5 wt% $TiO_2$ mixed with $Fe_2O_3$ showed a dendrite-shaped franklinite crystals caused by coalescence of small crystallites.

• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.79-84
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• 2013

The seawater pipes in the engine rooms of ships are surrounded by severely corrosive environments caused by fast flowing seawater containing chloride ions, high conductivity, etc. Therefore, it has been reported that seawater leakage often occurs at a seawater pipe because of local corrosion. In addition, the leakage area is usually welded using shielded metal arc welding with various electrodes. In this study, when seawater pipes were welded with four types of electrodes(E4311, E4301, E4313, and E4316), the difference between the corrosion resistance values in their welding zones was investigated using an electrochemical method. Although the corrosion potential of a weld metal zone welded with the E4316 electrode showed the lowest value compared to the other electrodes, its corrosion resistance exhibited the best value compared to the other electrodes. In addition, a heat affected zone welded with the E4316 electrode also appeared to have the best corrosion resistance among the electrodes. Furthermore, the corrosion resistance of the weld metal zone and heat affected zone exhibited relatively better properties than that of the base metal zone in all of the cases welded with the four types of electrodes. Furthermore, the hardness values of all the weld metal zones were higher than the base metal zone.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.802-807
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• 2012

The autothermal reforming of methane to syngas has been carried out in a reactor charged with both a Ni (15 wt%)-Ru (1 wt%)/$Al_2O_3$-MgO metallic monolith catalyst and an electrically-heated convertor (EHC). The standalone type reactor has a start-up time of less than 2 min with the reactant gas of $700^{\circ}C$ fed to the autothermal reactor. The $O_2/CH_4$ and $H_2O/CH_4$ ratio governed the methane conversion and temperature profile of reactor. The reactor temperature increased as the reaction shifted from endothermic to exothermic reaction with decreasing $H_2O/CH_4$ ratio. Also the amount of $CO_2$ in the products increases with increasing $H_2O/CH_4$ ratio due to water gas shift reaction. The 97% of $CH_4$ conversion was obtained and the reactor temperature was maintained $600^{\circ}C$ at the condition of $GHSV=10,000\;h^{-1}$ and feed ratio ($H_2O/CH_4=0.6$ and $O_2/CH_4=0.5$). In this condition, the maximum flow rate of the syngas generated from the reactor charged with 170 cc of the metallic monolith catalyst is $0.94\;Nm^3/h$.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.150-156
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• 2014

In this study, we implemented a research for improving performance of redox flow battery (RFB) via enhancing reaction rate of vanadium reaction ($[VO]^{2+}/[VO_2]^+$) that was a rate determining step. For doing that, porous catalyst, CMK3 was employed and its perfoamance was compared with that of Vulcan(XC-72) and commercial Pt/C (Johnson-Matthey Pt 20wt.%). Cyclic voltammetry (CV) was used for inspecting reactivity, while its structural feature was measured by TEM and BET&BJH. Also, Charge-discharge trend was evaluated by single cell tests. As result, CMK3 showed 6 times better catalytic activity and twice better reversibility than Vulcan(XC-72), while it showed larger surface area than Vulcan XR due to its porous structure. Furthermore, CMK3 indicated 85% of reactivity and reversibility of commercial Pt/C despite its Pt-less situation. In single cell tests, when RFB adopted CMK3 as catalyst for positive electrode, its charge-discharge curve result was better than that adopted commercial Pt/C.

• Proceedings of the Korean Quaternary Association Conference
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• 2004.06a
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• pp.46-46
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• 2004

Van Mijenfjorden은 스발바드 군도의 Spitsbergen 서부에 위치하는 두 번째로 큰 피오르드로 온난하고 염분도가 높은 북대서양의 표층수가 북극해로 유입되는 Gateway에 위치하기 때문에 전지구적이며 지역적인 기후변화의 영향을 받는 지역이다. 1999년 IMAGES 프로그램의 일환으로 프랑스 탐사선인 'R/V Marion Dufresne'을 이용하여 북극해의 스발바드 군도에 위치하는 Van Mijenfjorden (77$^{\circ}$ 46.87'N and 15$^{\circ}$ 17.81'E)에서 약 18m의 빙ㆍ해양 퇴적물 코아(MD99-2305)를 시추하여 마지막 최대 빙하기 이후의 고환경변화를 연구하였다. AMS 14C 연대 측정에 의하면 diamicton 층인 하부 2m를 제외한 16m의 퇴적층은 지난 12cal. ka BP경에 피오르드에 존재하던 조수빙하(tidewater glacier)가 해빙되기 시작한 이후에 퇴적되었다. 특히 유기지화학 자료와 부유성과 저서성 유공충의 산출양상 그리고 저서성 유공충인 C. reniforme의 산소ㆍ탄소 안정동위원소 비에 의하면 코아 MD99-2305에는 Van Mijenfjorden에서 홀로세 동안에 일어난 퇴적환경변화를 잘 기록하고 있다. 특히 홀로세 동안에 피오르드내의 퇴적환경 변화는 조수빙하의 확장과 후퇴와 밀접한 관계가 있으며, 유기물의 탄소동위원소(13Corg) 비는 -24에서 -22$\textperthousand$ 값의 변화를 보인다. 이는 Van Mijenfjorden 퇴적물에 공급된 유기물은 육상과 해양기원이 혼합되어 퇴적되었음을 지시한다. 지난 12 cal. ka BP 이후 13Corg 값이 뚜렷하게 변하는 것은 Van Mijenfiorden에서 조수빙하의 변동과 표층수에서의 생산력의 변화를 강하게 반영한다. 강하게 반영한다.53%가 이공계 출신, 100대 기업 CEO의 38.4%가 이공계 출신, 대입수능시험에서 자연계 지원비율이 감소 -40.1%('99)\$\longrightarrow$34.7%('00)\$\longrightarrow$29.4%('01)\$\longrightarrow$26.9%('02)\$\longrightarrow$30.3%('03)\$\longrightarrow$31.5%\$\longrightarrow$'04)필요성, 효과적인 운전자 교육 정책 등이 그것이다. 자동차 긴급 피난 차선은 유용한 시설로 여러곳에서 그 기능이 발휘되고 있으므로 많은 고속도로 관계자들은 설계, 시공 및 유지 관리 측면에서 유의해야 할 것이다.미세조직을 광학현미경으로 압출방향에 평행한 방향과 수직방향으로 관찰하였고, 열간 압출재 이방성을 검토하기 위하여 X선 회절분석을 실실하여 결정방위를 확인하였다. 전기 비저항 및 Seebeck 계수 측정을 위하여 각각 2$\times$2$\times$10$mm^3$ 그리고 5$\times$5$\times$10TEX>$mm^3$ 크기의 시편을 준비하였다.준비하였다.전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다.se that were all low in two aspects, named "the Nonsignificant group". And the issues were

• Analytical Science and Technology
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• v.12 no.2
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• pp.141-150
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• 1999

Twenty organic chemical substances, tetrachloroethylene, toluene, ethylbenzene, p-xylene, m-xylene, isopropyl benzene, stylene, bromobenzene, 1,3,5-trimethylbenzene, 2-chlorotoluene 1,2,4-trimethylbenzene, p-isopropyltoluene, 4-chlorotoluene, n-butylbenzene, 1,2,4-trichlorobenzene, naphthalene, tert-butylbenzene, sec-butylbenzene, phenol, isopropyl benzene hydroperoxide were isolated from untreated and treated wastewater collected at 76 companys of 9 types industry in the basin of Young San River. Their organic compounds were elucidated by Gas Chromatography/Mass Spectrometry (GC/MS) and by comparison with each standard reagents. Especially, phenol compound is detected from effluent water but not detected from plant wastewater in the chemical industry. Heavy metal, which are Cr, Mn, Cu, Zn, Cd, Pb, As, Al and Fe, are contained in the plant wastewater of all industry, Fe, Al of them is more detected than the other metals in plant wastewater. Cr, Cd, Pb, As is contained much in plant wastewater of electricity and electron, metal molding industry. Nine metals is nearely treated when plant wastewater is treated, and then the concentration of each other metals is detected below water quality standard or not detected by using AA.