• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.105-105
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• 2012

We have developed a photoemission-assisted plasma-enhanced chemical vapor deposition (PAPE-CVD) [1,2], in which photoelectrons emitting from the substrate surface irradiated with UV light ($h{\nu}$=7.2 eV) from a Xe excimer lamp are utilized as a trigger for generating DC discharge plasma as depicted in Fig. 1. As a result, photoemission-assisted plasma can appear just above the substrate surface with a limited interval between the substrate and the electrode (~10 mm), enabling us to suppress effectively the unintended deposition of soot on the chamber walls, to increase the deposition rate, and to decrease drastically the electric power consumption. In case of the deposition of DLC gate insulator films for the top-gate graphene channel FET, plasma discharge power is reduced down to as low as 0.01W, giving rise to decrease significantly the plasma-induced damage on the graphene channel [3]. In addition, DLC thickness can be precisely controlled in an atomic scale and dielectric constant is also changed from low ${\kappa}$ for the passivation layer to high ${\kappa}$ for the gate insulator. On the other hand, negative electron affinity (NEA) of a hydrogen-terminated diamond surface is attractive and of practical importance for PAPECVD, because the diamond surface under PAPE-CVD with H2-diluted (about 1%) CH4 gas is exposed to a lot of hydrogen radicals and therefore can perform as a high-efficiency electron emitter due to NEA. In fact, we observed a large change of discharge current between with and without hydrogen termination. It is noted that photoelectrons are emitted from the SiO2 (350 nm)/Si interface with 7.2-eV UV light, making it possible to grow few-layer graphene on the thick SiO2 surface with no transition layer of amorphous carbon by means of PAPE-CVD without any metal catalyst.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.440-440
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• 2012

Nanomaterials have emerged as new building blocks to construct light energy harvesting assemblies. Size dependent properties provide the basis for developing new and effective systems with semiconductor nanoparticles, quantized charging effects in metal nanoparticle or their combinations in 2 and 3 dimensions for expanding the possibility of developing new strategies for photovoltaic system. As top-down approach, we developed a simple and effective method for the large scale formation of self-assembled Cu(In,Ga)$Se_2$ (CIGS) nanostructures by ion beam irradiation. The compositional changes and morphological evolution were observed as a function of the irradiation time. As the ion irradiation time increased, the nano-dots were transformed into a nano-ridge structure due to the difference in the sputtering yields and diffusion rates of each element and the competition between sputtering and diffusion processes during irradiation. As bottom-up approach, we developed the growth of CIGS nanowires using thermal-chemical vapor deposition (CVD) method. Vapor-phase synthesis is probably the most extensively explored approach to the formation of 1D nanostructures such as whiskers, nanorods, and nanowires. However, unlike binary or ternary chalcogenides, the synthesis of quaternary CIGS nanostructures is challenging because of the difficulty in controlling the stoichiometry and phase structure. We introduced a method for synthesis of the single crystalline CIGS nanowires in the form of chalcopyrite using thermal-CVD without catalyst. It was confirmed that the CIGS nanowires are epitaxially grown on a sapphire substrate, having a length ranged from 3 to 100 micrometers and a diameter from 30 to 500 nm.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.376-376
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• 2012

Semiconductor nanowires (NWs) are future building block for nano-scale devices. Especially, Ge NWs are fascinated material due to the high electrical conductivity with high carrier mobility. It is strong candidate material for post-CMOS technology. However, thermal stability of Ge NWs are poor than conventional semiconductor material such as Si. Especially, when it reduced size as small as nano-scale it will be melted around CMOS process temperature due to the melting point depression. Recently, Graphene have been intensively interested since it has high carrier mobility with single atomic thickness. In addition, it is chemically very stable due to the $sp^2$ hybridization. Graphene films shows good protecting layer for oxidation resistance and corrosion resistance of metal surface using its chemical properties. Recently, we successfully demonstrated CVD growth of monolayer graphene using Ge catalyst. Using our growth method, we synthesized Ge/graphene core/shell (Ge@G) NW and conducted it for highly thermal stability required devices. We confirm the existence of graphene shell and morphology of NWs using SEM, TEM and Raman spectra. SEM and TEM images clearly show very thin graphene shell. We annealed NWs in vacuum at high temperature. Our results indicated that surface melting phenomena of Ge NWs due to the high surface energy from curvature of NWs start around $550^{\circ}C$ which is $270^{\circ}C$ lower than bulk melting point. When we increases annealing temperature, tip of Ge NWs start to make sphere shape in order to reduce its surface energy. On the contrary, Ge@G NWs prevent surface melting of Ge NWs and no Ge spheres generated. Furthermore, we fabricated filed emission devices using pure Ge NWs and Ge@G NWs. Compare with pure Ge NWs, graphene protected Ge NWs show enhancement of reliability. This growth approach serves a thermal stability enhancement of semiconductor NWs.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.123.2-123.2
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• 2010

Fuel Cell cogeneration system is a promising technology for generating electricity and heat with high efficiency of low pollutant emission. We have been developed 5kW class fuel cell cogeneration system for commercial and residential application. The fuel processor is a crucial part of producing hydrogen from the fossil fuels such as LNG and LPG. The 5kW class high efficiency fuel processor consists of steam reformer, CO shift converter, CO preferential oxidation(PrOx) reactor, burner and heat exchanger. The one-stage CO shift converter process using a metal oxide catalyst was adopted. The efficiency of 5 kW class fuel processor shows 75% based on LHV. In addition, for the purpose of continuous operation with load fluctuations in the commercial system for residential use, load change of fuel processor was tested. Efficiency of 30%, 50%, 70% and 100% load shows 75%, 75%, 73% and 72%(LHV), respectively. Also, during the load change conditions, the product gas composition was stable and the outlet CO concentration was below 5 ppm. The Fuel processor operation was carried out in residential fuel cell cogeneration system with fuel cell stack under dynamic conditions. The 5kW class fuel processor have been evaluated for long-term durability and reliability test including with improvement in optimal operation logic.

• Bulletin of the Korean Chemical Society
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• 제35권9호
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• pp.2649-2654
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• 2014

Synthesis of north-5'-methylbicyclo[3.1.0]hexyl adenine and hypoxanthine nucleosides with an ethenyl group at C3' position was successfully achieved by a highly facile method. Methylbicyclo[3.1.0]hexanone (${\pm}$)-7 with three contiguous chiral centers and its epimer (${\pm}$)-6 was remarkably simply constructed only by four steps involving a carbenoid insertion reaction in the presence of rhodium (II) acetate dimer as a metal catalyst, giving a correct relative stereochemistry of the generated three chiral centers. Due to steric hindrance from the concave face of the bicyclo[3.1.0]hexanone system, a Grignard reaction of (${\pm}$)-7 with ethenylmagnesium bromide showed exclusive diastereoselectivity towards the b-face. The Grignard reaction chemoselectively proceeded without reacting with ester functionality. Coupling reaction of glycosyl donor (${\pm}$)-11 with 6-chloropurine nucleobase afforded only the desired $N^9$-alkylated nucleoside without the formation of $N^7$-regioisomer. By the conventional method, 6-chloro group was converted into 6-amino and 6-hydroxy groups to give the desired adenine and hypoxanthine bicyclo[3.1.0]hexyl carbanucleosides with 3'-ethenyl group, respectively.

• Bulletin of the Korean Chemical Society
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• 제35권9호
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• pp.2726-2732
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• 2014

The promoting effect of rhodium on the structure and activity of the supported Cu-Co based catalysts for CO hydrogenation was investigated in detail. The samples were characterized by DRIFTS, $N_2$-adsorption, XRD, $H_2$-TPR, $H_2$-TPD and XPS. The results indicated that the introduction of rhodium to Cu-Co catalysts resulted in modification of metal dispersion, reducibility and crystal structure. DRIFTS results of CO hydrogenation at reaction condition (P=2 MPa, $T=260^{\circ}C$) indicated the addition of 1 wt % rhodium improved hydrogenation ability of Cu-Co catalysts. The ethanol selectivity and CO conversion were both improved by 1 wt % Rh promoted Cu-Co based catalysts. The alcohol distribution over un-promoted and rhodium promoted Cu-Co based catalysts obeys A-S-F rule and higher chain growth probability was got on rhodium promoted catalyst.

• 한국수소및신에너지학회논문집
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• 제12권4호
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• pp.277-285
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• 2001

본 논문은 연료전지 자동차용 10kWe급 정제일체형 메탄올개질기에 대한 연구결과이다. 이 개질기에서는 메탄올이 수증기와 반응하켜 수소를 포함한 혼합가스로 개질되고, 그 혼합가스는 다시 Palladium 합금막을 통하여 순수한 수소로 분리된다. 정제되고 남은 폐 가스중 가연성분들은 wire-mesh 형태의 연소촉매상에서 연소되어 개질반응에 필요한 열을 직접 공급함으로써 높은 메탄올 전환율, 고품질의 수소생산, 그리고 높은 시스템 열효율을 가능하게 한다. 동시에 이러한 개질, 분리 및 연소반응이 하나의 반응기에서 일어나 전체 시스템이 소형화될 수 있으며 운전이 용이한 장점도 있다. 본 연구팀에서 개발한 10kWe급 시스템은 운전연구를 통하여 수소생산량은 $8.2Nm^3/hr$ (10kWe급), 수소순도 99.999% 이상, CO 농도 5 ppm 미만, 총합열효율 81%, 초기기동 소요시간 20분, 부하변동웅답 1 분 이내를 달성했으며, 장처의 크기와 무게는 각각 16 L, 25 kg 이다.

• 공업화학
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• 제2권3호
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• pp.279-288
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• 1991

몇 종류의 산화물을 혼합하여 그 장점들이 촉매의 특성으로 나타나도록 하는 복합산화물 촉매의 한 종류로서 스피넬 구조를 이루는 Mg- 및 Zn-페라이트를 촉매로 선정하여 Cr 치환에 따른 물성을 분석하고, 에틸벤젠의 탈수소 반응에 대하여 연구하였다. 촉매의 특성 분석에는 XRD, BET, TG/DTA, ESCA, TEM, TPD등의 분석법을 사용하였다. 페라이트 촉매에 대한 Cr 치환 효과를 검토하기 위하여 물성을 종합적으로 분석한 결과, 표면으로의 확산이 용이한 Cr 은 촉매의 표면적 증가와 구조의 안정성에 기여하는 구조적인 조촉매로서 작용하였다. 촉매의 반응성 실험에 있어서는 Cr의 치환에 따른 활성변화를 검토하였는데, $MgCr_xFe_{2-x}O_4$ 촉매에서 Cr 치환량이 증가할수록 산소의 유동성이 작아져 완전산화반응이 억제되고 스티렌으로의 선택도가 증가하였다.

• 공업화학
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• 제7권5호
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• pp.813-822
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• 1996

온실효과에 주요한 기여를 하는 이산화탄소를 줄이기 위하여 새로운 형태의 고분자인 폴리(알킬렌 카보네이트)가 합성되어졌다. 이산화탄소와 여러 가지 에폭시드로부터 칼복시산의 아연염을 촉매로 하여 교대 공중합체가 만들어졌다. 중합체의 수 평균 분자량은 50,000 정도이면 중합 분산도는 5~10 정도로 비교적 넓은 분포를 갖는다. 이 중합체는 비 결정성이고, 투명한 물질로써 열분해가 쉽게 일어난다. 높은 온도와 불활성 분위기 하에서도 완벽한 분해가 일어나 탄소 잔류물을 남기지 않는 것으로 알려졌다. 간단한 에폭시드와의 공중합체의 물리적인 성질을 개선하기 위하여 입체 장애가 큰 에폭시드와의 삼원 공중합체도 만들 수 있다. 이러한 분해성을 이용하여 세라믹, 금속, 전자 산업용 바인더나 lost-foam casting에 활용이 검토되었다. 또한 포장용 필름이나 가소제로의 활용도 연구될 수 있을 것으로 기대된다.

• 한국재료학회지
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• 제26권5호
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• pp.250-257
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• 2016

Octahedral $Co_3O_4$/carbon nanofiber (CNF) composites are fabricated using electrospinning and hydrothermal methods. Their morphological characteristics, chemical bonding states, and electrochemical properties are used to demonstrate the improved photovoltaic properties of the samples. Octahedral $Co_3O_4$ grown on CNFs is based on metallic Co nanoparticles acting as seeds in the CNFs, which seeds are directly related to the high performance of DSSCs. The octahedral $Co_3O_4$/CNFs composites exhibit high photocurrent density ($12.73mA/m^2$), superb fill factor (62.1 %), and excellent power conversion efficiency (5.61 %) compared to those characteristics of commercial $Co_3O_4$, conventional CNFs, and metallic Co-seed/CNFs. These results can be described as stemmnig from the synergistic effect of the porous and graphitized matrix formed by catalytic graphitization using the metal cobalt catalyst on CNFs, which leads to an increase in the catalytic activity for the reduction of triiodide ions. Therefore, octahedral $Co_3O_4$/CNFs composites can be used as a counter electrode for Pt-free dye-sensitized solar cells.