• Applied Microscopy
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• 제50권
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• pp.17.1-17.9
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• 2020

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70% at 10 kV, slightly lower than that of the planar device (≈ 81%). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 센서 박막재료 반도체재료 기술교육
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• pp.70-73
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• 2002

Thin films of vanadium oxide($VO_{x}$) have been deposited by r.f. magnetron sputtering from $V_{2}O_{5}$ target in gas mixture of argon and oxygen. The oxygen/(oxygen+argon) partial pressure ratio of 0% and 8% is adopted. Crystal structure, chemical composition, molecular structure and optical properties of films sputter-deposited under different oxygen gas pressures and in-situ annealed in vacuum at $400^{\circ}C$ for 1h and 4h are characterized through XRD. RBS, FTlR and optical absorption measurements. The films as-deposited are amorphous and those annealed for time longer than 4h are polycrystalline. $V_{2}O_{5}$ and lower oxides co-exist in sputter-deposited films and as the oxygen partial pressure is increased the films become more stoichiometric $V_{2}O_{5}$. When annealed at $400^{\circ}C$, the as-deposited films are reduced to a lower oxide. It is observed that the oxygen atoms located on the V-O plane of $V_{2}O_{5}$ layer participate more readily in the oxidation and reduction process. The optical transmission of the films annealed in vacuum decreases considerably than the as-deposited films and the optical absorption of all the films increases rapidly between 400 and 550nm.

• Asian Journal of Atmospheric Environment
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• 제8권1호
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• pp.15-24
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• 2014

The capital city of Himalayan Country Nepal, Kathmandu Valley is surrounded by consecutive high mountains, which limits the air distribution and mixing effects significantly. It in turn generates steady air flow pattern over a year except in monsoon season. The air shed in the Valley is easily trapped by the surrounded mountains and the inversion layer formulated as the cap. The $PM_{10}$ concentration was noticeably higher than the standard level (120 ${\mu}g/m^3$) in urban and suburban area of Kathmandu valley for all seasons except monsoon period. The Valley area experiences similar wind patterns (W, WWS, and S) for a year but the Easterly wind prevails only during the monsoon period. There was low and calm wind blows during the winter season. Because of this air flow structure, the air emission from various sources is accumulated within the valley air, high level of air pollution is frequently recorded with other air polluted cities over the world. In this Valley area, brick kilns are recognized as the major air pollution source followed by vehicles. Mostly Bull Trench Kiln (BKT), Hoffman Kiln and Vertical Shaft Brick Kiln (VSBK) are in operation for brick firing in Kathmandu valley where the fuels such as crushed coal, saw dust, and natural gas are used for processing bricks in this study. Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) was used for screening and quantifying the potential impacts of air emission from firing fuels. The total Environmental Performance Score (EPS) was estimated and the EPS of coal was approximately 2.5 times higher than those of natural gas and saw dust. It is concluded that the crushed coal has more negative impact to the environment and human health than other fuel sources. Concerning the human health and environment point of view, alternative environment friendly firing fuel need to be used for brick industry in the kiln and the air pollution control devices also need to be applied for minimizing the air emissions from the kilns.

• Korean Chemical Engineering Research
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• 제47권1호
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• pp.79-83
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• 2009

본 연구에서 고밀도 플라즈마 식각 장치를 사용한 비정질 실리콘 막의 게이트 전극선 형성공정에서 여러 가지 식각 변수가 치수 제어와 식각 속도 및 식각 선택비 등 식각 특성에 미치는 영향을 분석하였다. $Cl_2/HBr/O_2$로 구성된 식각 기체의 전체 유량을 증가시키면 비정질 실리콘의 식각 속도가 증가하나 식각 전후의 형상치수는 변화없이 거의 일정하였다. 전체 유량을 고정시키고 $Cl_2$와 HBr 간의 유량비를 변화시키면 HBr의 유량이 커질수록 비정질 실리콘의 식각 속도가 감소하였다. $O_2$의 유량을 증가시키면 산화막의 식각 속도가 상대적으로 낮아져 식각 선택비를 증가시켜 식각 공정의 안정성을 높이나 게이트 전극선을 경사지게 하는 특성을 보인다. Source power의 증가는 비정질 실리콘 식각 속도의 증가와 더불어 형상치수의 증가를 가져오며, bias power의 증가는 비정질 실리콘과 산화막의 식각 속도를 증가시키나 식각 선택비를 크게 감소시키는 경향을 보였다.

• 한국재료학회지
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• 제21권11호
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• 한국분말재료학회지
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• 제24권3호
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• 한국유체기계학회 논문집
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• 제5권1호
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• pp.49-54
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• 2002

HANARO, 30 MW of research reactor, was installed at the depth of 13m in an open pool. The $90\%$ of primary coolant was designed to pass through the core and to remove the reaction heat of the cote. The rest, $10\%$, of the primary coolant was designed to bypass the core. And the reactor coolant through and bypass the core was inhaled at the top of chimney by the coolant pump to prevent the radiated gas from being lifted to the top of reactor pool. But, the part of core bypass coolant was not inhaled by the reactor coolant pump and reached at the top of reactor pool by natural convection, and increased the radiation lovel on the top of reactor pool. To reduce the radiation level by protecting the natural convection of the core bypass flow, the hot water layer (HWL, hereinafter) was installed with the depth of 1.2 m from the top of reactor pool. As the HWL was normally operated, the radiation level was reduced to five percent ($5\%$) in comparing with that before the installation of the HWL. When HANARO was operated at a higher temperature than the normal temperature of the HWL by operating the standby heater, it was found that the radiation level was more reduced than that before operation. To verify the reason, the heat loss of the HWL was calculated by Visual Basic Program. It was confirmed through the results that the larger the temperature difference between the HWL and reactor hall was, the more the evaporation loss increased. And it was verified that the radiation level above was reduced mote safely by increasing the capacity of heater.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.221-226
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• 2001

HANARO, 30MW of research reactor, was installed at the depth of 13m of open pool, The $90\%$ of primary coolant was designed to pass through the core and to remove the reaction heat of the core. The rest $10\%$, of the primary coolant was designed to bypass the core. And the reactor coolant through and bypass the core was inhaled at the top of chimney by the coolant pump to protect that the radiated gas was lifted to the top of reactor pool. But, the part of core bypass coolant was not inhaled by the reactor coolant pump and reached at the top of reactor pool by natural convection and increased the radiation level on the top of reactor pool. To reduce the radiation level by protecting the natural convection of the core bypass flow, the hot water layer (HWL, hereinafter) was installed with the depth of 1.2m from the top of reactor pool. As the HWL was normally operated, the radiation level was reduced to five percent ($5\%$) in comparing with that before the installation of the HWL. When HANARO was operated with higher temperature than the normal temperature of the HWL by operating the standby heater, it was found that the radiation level was more reduced than that before operation. To verify the reason, the heat loss of the HWL was calculated. It was confirmed through the results that the larger the temperature difference between the HWL and reactor hall was, the more the evaporation loss was increased. And it was verified that the radiation level above was reduced more safely by increasing the capacity of heater.

• 한국표면공학회지
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• 제54권6호
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• pp.365-370
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• 2021

In this research, we proceeded with research on plasma resistance of the cleaning process of APS(Atmospheric Plasma Spray)-Y₂O₃ coated parts used for semiconductor and display plasma process equipment. CF₄, O₂, and Ar mixed gas were used for the plasma environment, and respective alconox, surfactant, and piranha solution was used for the cleaning process. After APS-Y₂O₃ was exposed to CF₄ plasma, the surface changed from Y₂O₃ to YF₃ and a large amount of carbon was deposited. For this reason, the plasma corrosion resistance was lowered and contamination particles were generated. We performed a cleaning process to remove the defect-inducing surface YF₃ layer and carbon layer. Among three cleaning solutions, the piranha cleaning process had the highest detergency and the alconox cleaning process had the lowest detergency. Such results could be confirmed through the etching amount, morphology, composition, and accumulated contamination particle analysis results. Piranha cleaning process showed the highest detergency, but due to the very large thickness reduction, the base metal was exposed and a large number of contaminated particles were generated. In contrast, the surfactant cleaning process exhibit excellent properties in terms of surface detergency, etching amount, and accumulated contamination particle analysis.

• 한국분말재료학회지
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• 제21권2호
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• pp.119-123
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• 2014

Pt has been widely used as catalyst for fuel cell and exhausted gas clean systems due to its high catalytic activity. Recently, there have been researches on fabricating composite materials of Pt as a method of reducing the amount of Pt due to its high price. One of the approaches for saving Pt used as catalyst is a core shell structure consisting of Pt layer on the core of the non-noble metal. In this study, the synthesis of Pt shell was conducted on the surface of $TiO_2$ particle, a non-noble material, by applying ultraviolet (UV) irradiation. Anatase $TiO_2$ particles with the average size of 20~30 nm were immersed in the ethanol dissolved with Pt precursor of $H_2PtCl_6{\cdot}6H_2O$ and exposed to UV irradiation with the wavelength of 365 nm. It was confirmed that Pt nano-particles were formed on the surface of $TiO_2$ particles by photochemical reduction of Pt ion from the solution. The morphology of the synthesized Pt@$TiO_2$ nano-composite was examined by TEM (Transmission Electron Microscopy).