• Journal of Korean Vacuum Science & Technology
• /
• 제3권2호
• /
• pp.116-120
• /
• 1999

Possible role of hydrogen atoms on the formation of microcrystalline silicon films was schematically investigated using a plasma enhanced chemical vapor deposition system. A layer-by-layer technique that can alternate deposition of ${\alpha}$-Si thin film and then exposure of H2 plasma was used for this end. The experimental process was extensively carried out under different hydrogen plasma times (t2) at a fixed number of 20 cycles in the deposition. structural properties, such as crystalline volume fractions and grain shapes were analyzed by using a Raman spectroscopy and a scanning electron microscopy. Electrical transports were characterized by the temperature dependence of the dark conductivity that gives rise to the calculation of activation energy (Ea). Optical absorption was measured using an ultra violet spectrophotometer, resulting in the optical energy gap (Eopt). Our experimental results indicate that both of the hydrogen etching and the structural relaxation effects on the film surface seem to be responsible for the growth mechanism of the crystallites in the ${\mu}$c-si films.

• 대한기계학회논문집B
• /
• 제31권10호
• /
• pp.832-839
• /
• 2007

The geometry and dimensions of an expansion chamber are decisive factors in thermal puffer plasma chamber designs. Because they together dominate the temperature and speed at which the cooling gas from the chamber flows back through a flow channel to the arcing zone for the successful interruption of fault currents. In this study, we calculated the flow and mass transfer driven by arc plasma, and investigated the effects of a flow guide installed inside a thermal puffer plasma chamber. It is found that the existing cold gas of the chamber mixes with hot gases entrained from the arcing zone and is subjected to compression due to pressure build-up in the chamber. The pressure build-up with the flow guide is larger than that without due to a vortex which rotates clockwise around the chamber center. By the reverse pressure gradient, the mixing gas of the chamber flows back out for cooling down the residual plasma near current zero. In the case with the flow guide, the temperature just before current zero is lower than that without, and the Cu concentration with high electrical conductivity is also less than that without the flow guide.

• 마이크로전자및패키징학회지
• /
• 제29권4호
• /
• pp.63-69
• /
• 2022

이산화 바나듐은 금속-절연체 전이라는 독특한 특성으로 인해 기초적인 소재 연구 및 산업에의 응용을 위한 연구가 꾸준하게 진행되고 있다. 본 연구에서는 통전활성소결법으로 제조한 이산화 바나듐의 금속-절연체 전이 특성에 마그네슘과 텅스텐 첨가가 미치는 영향을 연구하였으며, 덩어리 시편을 대상으로 그 거동을 고찰하였다. 상용 분말과 통전활성소결법을 이용하여 열처리를 진행하여 제작한 시편의 경우 격자 상수의 변화는 크지 않고 이차상이 존재하였으며, 이로 인해 상전이 온도는 64.2-64.6℃에 분포하는 것으로 나타났다. 반면 불순물의 종류와 함량에 따라 전기전도도는 최대 2.4배 증가하거나 최대 57.4배 감소하는 거동을 나타냈다. 열전도도는 불순물의 첨가에 따라 증가하는 거동을 나타냈으며, 상전이 온도 이전에서는 1.8~2.5 W/m·K, 성전이 온도 이후에서는 1.9~2.8 W/m·K의 값을 가졌다. 이러한 물성 변화는 불순물의 첨가로 인한 전하 나르개 농도의 변화, 불순물의 산란중심, 미세구조의 변화 등이 복합적으로 작용한 결과로 해석할 수 있다.

• Carbon letters
• /
• 제12권4호
• /
• pp.185-193
• /
• 2011

Carbon nanotubes (CNTs) have developed into one of the most competitively researched nano-materials of this decade because of their structural uniqueness and excellent physical properties such as nanoscale one dimensionality, high aspect ratio, high mechanical strength, thermal conductivity and excellent electrical conductivity. Mass production and structure control of CNTs are key factors for a feasible CNT industry. Water and ethanol vapor enhance the catalytic activity for massive growth of vertically aligned CNTs. A shower system for gas flow improves the growth of vertically aligned single walled CNTs (SWCNTs) by controlling the gas flow direction. Delivery of gases from the top of the nanotubes enables direct and precise supply of carbon source and water vapor to the catalysts. High quality vertically aligned SWCNTs synthesized using plasma enhance the chemical vapor deposition technique on substrate with suitable metal catalyst particles. This review provides an introduction to the concept of the growth of vertically aligned SWCNTs and covers advanced topics on the controlled synthesis of vertically aligned SWCNTs.

• 한국분말재료학회지
• /
• 제11권2호
• /
• pp.158-164
• /
• 2004

W-Cu composite has been used for the applications requiring both high strength, good thermal and electrical conductivity. A graded combination of W and Cu will reduce thermal stress concerned with heat conduction, maintaining good thermal conductivity and high mechanical strength. In the present work, an attempt was made to fabricate continuous W-Cu FGM by preparing the graded porous structure of W skeleton using spark plasma sintering (SPS) process followed by infiltrating Cu. The graded porous structure was prepared at 150$0^{\circ}C$ for 60s under pressure of 15MPa by SPS process using a graphite mold with varying crr)ss section in the longitudinal direction. Infiltration of Cu was performed at 115$0^{\circ}C$ for 1 hour under $H_2$. W-Cu composite with graded Cu composition of 14 to 27 wt％ was finally prepared. In this process the gradient of composition could be conveniently controlled by varying the gradient of cross sectional area of graphite mold, temperature and pressure.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 연구회
• /
• pp.201-203
• /
• 2001

This paper describes the information for quantitative simulation of weakly ionized plasma. We must grasp the meaning of the plasma state condition to utilize engineering application and to understand materials of plasma state. In this paper, the drift velocity of electron in Xenon gas calculated for range of E/N values from 0.01~500[Td] at the temperature is $300[^{\circ}K]$ and pressure is 1[Torr], using a set of electron collision cross sections determined by the authors and the values of drift velocity of electrons are obtained for TOF, PT, SST sampling method of Backward Prolongation by two term approximation Boltzmann equation method. it has also been used to predict swarm parameter using the values of cross section as input. The result of Boltzmann equation, the drift velocity of electrons, has been compared with experimental data by L. S. Frost and A. V. Phelps for a range of E/N. The swarm parameter from the study are expected to server as a critical test of current theories of low energy scattering by atoms and molecules.

• 한국표면공학회지
• /
• 제30권5호
• /
• pp.333-346
• /
• 1997

Plasma spray processes for functional coatings of tubular SOFC ( Soild oxide Fuel Cell).consisting of air electrode, oxide electrolyte, an fuel electrode, are optimized by fully saturated fractional factorial testing. Material and electric characteristics of each coating are analtsed by the implementation of SEM and optical microscope for evaluating microstructure and porosity, X-ray diffraction method for investigating compositional change between raw powder and sprayed coating, and Van der Pauw method for measuring electrical conductivity. LSM ($La_{0.65}Sr_{0.35}MnO_3$air electrode and Ni-YSL fuel electrode coatings have porosities of around 23~30% sufficient for effective fuel and oxidant gas supply to electrochemical reaction interfaces and electrical conductivities of around 90 S/cm and 1000 S/cm, respectively, enough for acting as current collecting electrodes. YSZ($ZrO_2-8mol%Y_2O_3$) electrolyte film has a high ionic conductivities of 0.05~0.07 S/cm at $1000^{\circ}C$ in air atmosphere, but appears to be somewhat too porous to reduce the thickness. for enhancing the cell efficiency. A unit tubular SOFC has beem fabricated by the optimized plasma spray processes for each functional coating and the cell. Its electrochemical chracteristics are investigated by measuring voltage-current and power density with variation of operationg temperature, radio of fuel to air gas flowrates, and total gas flowrate of reactants.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2011년도 제42회 하계학술대회
• /
• pp.1684-1685
• /
• 2011

This paper presents a theoretical and numerical analysis for thermal isolation of silicon micro-structures, especially for a large size with poor thermal conductivity, as well as straightforward solution for such an issue. Additional metal patterns underneath the silicon structures effectively reduces the thermal isolation. Heat transfer mechanism is analyzed using an equivalent circuit of thermal network including plasma, a heat source, heat capacitors, and thermal resistances. The FEM simulation was carried out to investigate the temperature change of silicon micro-structures according to process time. The temperature of silicon micro-structures with 2 ${\mu}m$ thick chrome layer at a steady state is $86^{\circ}C$, an approximately 40% decrease from the silicon microstructure without thin metal ($122^{\circ}C$)

• 한국기계가공학회지
• /
• 제12권6호
• /
• pp.3-9
• /
• 2013

Aluminum Oxide($Al_2O_3$) ceramics are excellent candidates for such applications due to their outstanding mechanical, thermal, and tribological properties. However, they are difficult to machine using conventional mechanical methods. Carbon fillers, such as carbon nanotubes(CNT) and graphene nanoplatelets(GNP)can be dispersed in a ceramic matrix to improve the mechanical and electrical properties. In this study, CNT and Graphene reinforced hybrid ceramic composites were fabricated using the spark plasma sintering method at a temperature of $1,500^{\circ}C$, pressure of 40 MPa, and soaking time of 10min. Besides this, the material properties such as microstructure, crystal structure, hardness, and electrical conductivity were analyzed using FE-SEM, XRD, Vickers, and the 4-point probe method. A micro machining test was carried out to compare the effects of the material properties and the machining performance for CNT and Graphene reinforced ceramic composites.

• 한국분말재료학회지
• /
• 제12권6호
• /
• pp.393-398
• /
• 2005

In-situ processing route was adopted to disperse carbon nanotubes (CNTs) into $Al_2O_3$ powders homogeneously. The $Al_2O_3$ composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for in-situ formation of CNTs on nano-sized Fe dispersed $Al_2O_3$ powders. CNTs/Fe/$Al_2O_3$ nanopowders were densified by spark plasma sintering (SPS). The hardness and bending strength as well as electrical conductivity increased with increasing sintering temperature. However, the electrical conductivity of the composites sintered at above $1500^{\circ}C$ showed decreased value with increasing sintering temperature due to the oxidation of CNTs.