• 한국결정성장학회지
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• 제27권6호
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• pp.282-288
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• 2017

본 논문에서는 광전 음극 이미지 센서로 사용될 수 있는 광소자용 재료로 III-V 족 화합물 반도체인 GaAs/AlGaAs 다층 구조를 LPE(Liquid Phase Epitaxy) 방법에 의해 성장하였다. n형 GaAs 기판 위에 수십 nm의 GaAs 완충층을 형성 한 후 Zn가 도핑된 p-AlGaAs 에칭 정지 층(etching stop layer)과 Zn가 도핑된 p-GaAs 층 그리고 Zn가 도핑된 p-AlGaAs 층을 성장하였다. 성장된 시료의 특성을 조사하기 위하여 주사전자현미경(SEM)과 이차이온질량분석기(SIMS) 그리고 홀(Hall) 측정 장치 등을 이용하여 GaAs/AlGaAs 다층 구조를 분석하였다. 그 결과 $1.25mm{\times}25mm$의 성장 기판에서 거울면(mirror surface)을 가지는 p-AlGaAs/p-GaAs/p-AlGaAs 다층 구조를 확인할 수 있었으며, Al 조성은 80 %로 측정 되었다. 또한 p-GaAs층의 캐리어 농도는 $8{\times}10^{18}/cm^2$ 범위까지 조절할 수 있음을 확인하였다. 이 결과로부터 LPE 방법에 의해 성장된 p-AlGaAs/p-GaAs/AlGaAs 다층 구조는 광전 음극 이미지 센서의 소자로서 이용될 수 있을 것으로 기대한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.145-145
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• 2011

Recently, multi-hole electrode RF capacitively coupled plasma discharge is being used in the deposition of microcrystalline silicon for thin film solar cell to increase the speed of deposition. To make efficient multi-hole electrode RF capacitively coupled plasma discharge, the hole diameter is to be designed concerning the plasma parameters. In past studies, the relationship between plasma parameters such as pressures and gas species, and hole diameter for efficient plasma density enhancement is experimentally shown. In the presentation, the relationship between plasma deriving frequency and hole diameter for efficient multi-hole electrode RF capacitively coupled plasma discharge is shown. In usual capacitively coupled plasma discharge, plasma parameter, such as plasma density, plasma impedence and plasma temperature, change as frequency increases. Because of the change, the optimum hole diameter of the multi-hole electrode RF capacitively coupled plasma for high density plasma is thought to be modified when the plasma deriving frequency changes. To see the frequency effect on the multi-hole RF capacitively coupled plasma is discharged and one of its electrode is changed from a plane electrode to a variety of multi-hole electrodes with different hole diameters. The discharge is derived by RF power source with various frequency and the plasma parameter is measured with RF compensated single Langmuir probe. The shrinkage of the hole diameter for efficient discharge is observed as the plasma deriving frequency increases.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.403-406
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• 2006

본 연구에서는 양극의 two-phase simulation 모델을 확립하고 GDL 물성과 작동조건이 전지성능에 미치는 영향에 대해 시행하였다. 모델로는 Multi-phase $mixture(M^2)$ 모델을 사용하였는데 이 모델은 각 상의 balance식을 하나의 mixture-phase식으로 통합하여 수학적 계산이 용이할 뿐만 아니라 실제 전지 성능에 매우 근사하여 신뢰성성도 확보할 수 있었다. 최적의 GDL 구조와 작동조건을 규명하기 위해 기체투과도, 접촉각, 기공도, 기체 공급가스 차이에 따른 전지 성능 분석을 시행하였는데 그 결과 모든 파라미터들이 증가할수록 비례적으로 전지 성능이 증가하였다. 기체 공급가스>기공도>>접촉각>기체투과도 순으로 전지에 미치는 영향이 큰 것으로 나타났다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1091-1091
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• 2005

• 소성∙가공
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• 제13권3호
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• pp.279-284
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• 2004

Electroforming is the highly specialized use of electrodeposition for the manufacture of metal parts and basically a specialized form of electroplating. So, we can apply electrochemical system analysis for electroforming process. Electrochemical systems are concerned with the interplay between electricity and chemistry, namely the measurements of electrical quantities, such as current density, potential, and charge, and their relationship to chemical parameters. This paper based on the basic equations of electrics and electrochemical kinetics, was employed for a theoretical explanation of the current density distribution on electroforming process. We calculated current density distribution and potential distribution on cathode. Also, calculated current density distribution of vertical direction. It was shown that current density is related with distance of between anode and cathode and mass transfer process.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
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• pp.486-489
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• 2007

Carbon nanotube (CNT) cathodes having a trench structure similar to the structure of the gated triodetype cathode were successfully fabricated by a screenprinting method with multi-walled carbon nanotubes. We observed that a liquid method not only readily removes the organic residues on the CNT films, but also satisfactorily protrudes the CNTs out of the electrode surface. The CNT cathodes prepared by the liquid method showed a turned-on field of $1.4\;V/{\mu}m$. The emission current density of them was about $3.1\;mA/cm^2$ at the electric field of $3\; V/{\mu}m$. The liquid method appears to be a promising surface treatment of CNT cathode for gated triode-type FEDs applications.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.33-36
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• 2008

The transient behavior of a passive air breathing direct methanol fuel cell (DMFC) operated on vapor-feeding mode is studied in this paper. It generally takes 30 minutes after starting for the cell response to come to its steady-state and the response is sometimes unstable. A mathematical dynamic one-dimensional model for simulating transient response of the DMFC is presented. In this model a DMFC is decomposed into its subsystems using lumped model and divided into five layers, namely the anodic diffusion layer, the anodic catalyst layer, the proton exchange membrane (PEM), the cathodic catalyst layer and the cathodic diffusion layer. All layers are considered to have finite thickness, and within every one of them a set of differential-algebraic governing equations are given to represent multi-components mass balance, such as methanol, water, oxygen and carbon dioxide, charge balance, the electrochemical reaction and mass transport phenomena. A one-dimensional, isothermal and mass transport model is developed that captures the coupling between water generation and transport, oxygen consumption and natural convection. The single cell is supplied by pure methanol vapor from a methanol reservoir at the anode, and the oxygen is supplied via natural air-breathing at the cathode. The water is not supplied from external source because the cell uses the water created at the cathode using water back diffusion through nafion membrane. As a result of simulation strong effects of water transport were found out. The model analysis provides several conclusions. The performance drop after peak point is caused by insufficiency of water at the anode. The excess water at the cathode makes performance recovery impossible. The undesired crossover of the reactant methanol through the PEM causes overpotential at the cathode and limits the feeding methanol concentration.

• 한국재료학회지
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• 제19권5호
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• pp.233-239
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• 2009

The electrocatalytic behavior of the PtCo catalyst supported on the multi-walled carbon nanotubes (MWNTs) has been evaluated and compared with commercial Pt/C catalyst in a polymer electrolyte membrane fuel cell(PEMFC). A PtCo/MWNTs electrocatalyst with a Pt:Co atomic ratio of 79:21 was synthesized and applied to a cathode of PEMFC. The structure and morphology of the synthesized PtCo/MWNTs electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. As a result of the X-ray studies, the crystal structure of a PtCo particle was determined to be a face-centered cubic(FCC) that was the same as the platinum structure. The particle size of PtCo in PtCo/MWNTs and Pt in Pt/C were 2.0 nm and 2.7 nm, respectively, which were calculated by Scherrer's formula from X-ray diffraction data. As a result we concluded that the specific surface activity of PtCo/MWNTs is superior to Pt/C's activity because of its smaller particle size. From the electrochemical impedance measurement, the membrane electrode assembly(MEA) fabricated with PtCo/MWNTs showed smaller anodic and cathodic activation losses than the MEA with Pt/C, although ohmic loss was the same as Pt/C. Finally, from the evaluation of cyclic voltammetry(CV), the unit cell using PtCo/MWNTs as the cathode electrocatalyst showed slightly higher fuel cell performance than the cell with a commercial Pt/C electrocatalyst.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.392-392
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• 2011

Carbon nanotubes (CNT) emitter has widely become an attractive mechanism that draws growing interests for cold cathode field emission.$^{1,2}$ CNT yarns have demonstrated its potential as excellent field emitters.$^3$ Extensive simulations were carried out in designing a CNT yarn-based cathode assembly. The focal spot size dependence on the anode surface of the geometric parameters such as axial distance of the electrostatic focus lens from the cathode and the applied bias voltages at the cathode, grid mesh and electrostatic focus lens were studied. The detailed computer simulations using Opera 3D electromagnetic software$^4$ had revealed that a remarkable size of focal spot under a focusing lens triode type set-up design was achieved. The result of this optimization simulation would then be applied for the construction of the CNT yarn based micro-focus x-ray tube with its field emission characteristics evaluated.

• 대한기계학회논문집A
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• 제35권7호
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• pp.729-736
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• 2011

TOPSIS(Technique for Order Preference by Similarity to Ideal Solution)는 상충되는 다수의 속성이 존재하는 상황에서 의사결정이 요구되는 다속성 의사결정법(Multi Attribute Decision Making) 중 하나이다. 이는 선택된 대체안이 최선의 이상적 대체안으로부터 가장 가까운 거리에 위치해야 하고, 동시에 부정적으로 이상적인 대체안으로부터는 가장 멀리 위치해야 한다는 논리에 입각한 의사결정 기법이다. TOPSIS 는 최소화와 최대화가 공존하는 다목적함수 형상 최적설계에 적용이 가능하다. 본 연구에서는 TOPSIS 와 베지어 곡선(Rational Bezier Curve)을 적용하여 CRT(Cathode Ray Tubes) 후면유리의 다중목적 형상최적설계를 수행하였다. 무게와 1 차 주응력의 두 가지 다중목적 함수를 최적화하기 위하여, 다중목적 함수의 성능지표를 TOPSIS 의 상대적 근접도로 정의하고 이를 반응표면모델로 구성하여 다중목적 형상최적설계가 가능한 방법론을 제안하였다. 이를 통해 하나의 최적해가 아닌 최적해의 군이 선정되어, 무게와 주응력 최적해의 모순관계를 확인하면서 다양한 설계요구 스펙을 만족시켜줄 수 있는 방안을 설계자가 스스로 선택하도록 하였다.