• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.258-262
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• 2005

We report on the field emission properties from vertically aligned carbon nanotubes (CNTs) produced by a triode PECVD with a SiNx capping layer on metal catalyst. It is found that the CNTs density can be controlled by the capping layer thickness and decreases with increasing SiNx thickness. The CNT density of $\~$ 104/$cm^{2}$ exhibited highest electron emission characteristics, the threshold field of 1.2 V/$\mu$m and the current density of 0.17 mA/$cm^{2}$ at 3.6 V/$\mu$m. We have carried out investigation of electron emission stability under ambient gas of N2. The electron emission stability was improved with decreasing CNT density. Under $1\times$$10^{-5}$ Torr ambient pressure, the CNTs in 5 $\mu$m hole show electron emission current higher than $1\times$$10^{-4}$ A/cm2 and it's electron emission uniformity has $2\%$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.941-945
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• 2006

In the development of electricity generating wind turbines for wind farm application, only two types have survived as the methods of power regulation; stall regulation and fun span pitch control. The sound measurement procedures of IEC 61400-11 are applied to field test and evaluation of noise emission from each of 1.5 MW and 660 kW wind turbine generators (WTG) utilizing the stall regulation and the pitch control for the power regulation, respectively. Apparent sound power level, wind speed dependence and third-octave band levels are evaluated for both of WTGs. It is found that while 1.5 MW WTG using the stall control is found to emit lower sound power than 660 kW one using the pitch control at low wind speed (below 8 m/s), sound power from the former becomes greater than that of the latter in the higher wind speed. Equivalent continuous sound pressure levels (ECSPL) of the stall control type of WTG vary more widely with wind speed than those of the pitch control type of WTG These characteristics are believed to be strongly dependent on the basic difference of the airflow around the blade between the stall regulation and the pitch control types of WTG. These characteristics according to the methods of power regulation lead to the very different noise emission characteristics of WTG depending on the seasons because the average wind speed in summer is lower than the critical velocity over which the airflow on the suction side of blade in the stall types of WT are separated. These results propose that, in view of environmental noise regulation, the developer of wind farm should give enough considerations to the choice of power regulation of their WTG based on the weather conditions of potential wind farm locations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.50-53
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• 2001

In this study, gate leakage current mechanism has been analyzed for GaAs MESFET with different temperatures ranging from 27$^{\circ}C$ to 300$^{\circ}C$ . It is expected that the thermionic and field emission at the MS contact will dominate the current flow. Thermal cycle is applied to test the reliability of the device. From the results, it is proved that thermal stress gradually increases the gate leakage current at the same bias conditions and leads to the breakdown and failure mechanism which is critical in the field equipment. Finally the gate contact under the repeated thermal shock has been tested to check the quality of Schottky barrier and the current will be expressed in the analytical from to associate with the electrical characteristics of the device.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.108-116
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• 2001

The in-cylinder flow field of gasoline engine comprises unsteady compressible turbulent flows caused by the intake port, combustion chamber geometry. Thus, the quantitative analysis of the in-cylinder flow characteristics plays an important role in the improvement of engine performances and the reduction of exhaust emission. In order to obtain the quantitative analysis of the in-cylinder gas flows for a gasoline engine, the single-frame particle tracking velocimetry was developed, which is designed to measure 2-dimensional gas flow field. In this paper, influences of the swirl and tumble intensifying valves on the in-cylinder flow characteristics under the various intake flow conditions were investigated by using this PTV method. Based on the results of experiment, the generation process of swirl and tumble flow in a cylinder during intake stroke was clarified. Its effect on the tumble ratio at the end of compression stroke was also investigated.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1137-1139
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• 1995

$SiN_x$ films deposited on bare Si and wet-etched Si by RPCVD were fabricated to investigated the effect of wet-etched surface of Si on the characteristics of the interface between $SiN_x$ and Si. FT-IR spectra on each film showed similar characteristics. However, it was confirmed that the electric characteristics(I-V, C-V) of the interface between $SiN_x$ and Si have been degraded by the wet etching process of Si, which is applied for the formation of Si field emitter array. Therefore, we suggest that the stacked structure of insulating layer with good interface characteristics is desirable for FED application.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.5
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• pp.15-24
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• 2013

Numerical studies were conducted to investigate the internal flow field and combustion characteristics of DISI engine with methanol blended in gasoline. Dual injection was applied and the characteristics were compared to single injection strategy. The amount of the fuel injection was corresponded to air-fuel ratio of each fuel for complete combustion. The preforming model in this study, software STAR-CD was employed for both modeling and solving. The operating speed condition were at 4000 rpm/WOT (Wide open throttle) where the engine was fully warmed. The results of single injection with M28 showed that the uniformity, equivalence ratio, in-cylinder pressure and temperature increased comparing to gasoline (M0). When dual injection was applied, there was no significant change in uniformity and equivalence ratio but the in-cylinder pressure and temperature increased. When M28 fuel and single injection was applied, the CO (Carbon monoxide) and NO (Nitrogen oxides) emission inside the combustion chamber increased approximately 36%, 9% comparing with benchmarking case in cylinder prior to TWC (Three Way Catalytic converter). When dual stage injection was applied, both CO and NO emission amount increased.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1597-1599
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• 2004

Carbon nanotubes (CNTs) are grown on the TiN-coated silicon substrate by varying the thickness of Ni and Invar426 catalyst layers at 600$^{\circ}C$ using an inductively coupled plasma-chemical vapor deposition (ICP-CVD). The Ni and Invar426 catalysts are formed using an RF magnetron sputtering system with various deposition periods. Characterization using various techniques, such as FESEM, HRTEM, and Raman spectroscopy, shows that the physical dimension as well as the crystal quality of grown CNTs are strongly changed by the kind and thickness of catalyst materials. It is also seen that Ni catalysts would be more desirable for vertical-alignment of CNTs compared with Invar426 catalysts. However, the CNTs using Invar426 catalysts display much better electron emission capabilities than those using Ni catalysts. The physical reason for all the measured data obtained are discussed to establish the relationship between structural properties and field-emissive properties of CNTs.

• Carbon letters
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• v.12 no.1
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• pp.48-52
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• 2011

The conducting polymer-coated multi-walled carbon nanotubes (MWCNTs) were prepared by template polymerization of aniline and pyrrole on the surface of MWCNTs in order to develop the novel electromagnetic interference (EMI) shielding materials. The conducting polymer phases formed on the surface of MWCNTs were confirmed by field emission-scanning electron microscopy and field emission-transmission electron microscopy. Both permittivity and permeability were significantly improved for the conducting polymer-coated MWCNTs due to the intrinsic electrical properties of MWCNTs and the conducting properties of coated polymers. The electromagnetic waves were effectively absorbed based on the permittivity nature of conducting polymer and MWCNTs preventing the secondary interference from reflecting the electromagnetic waves. The highly improved EMI shielding efficiency was also obtained for the conducting polymer-coated MWCNTs showing the synergistic effects by combining MWCNTs and the conducting polymers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.2
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• pp.101-105
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• 2007

We have synthesized silicon nanowires by using RFCVD(Radio Frequency Chemical Vapor Deposition) system on Au deposited p-type Si(100) wafers, and investigated their physical and electrical properties. The silicon nanowires had been grown in the atmospheres of $H_{2},\;N_{2}\;and\;SiH_{4}$ at 10 Torr at the substrate temperatures of $700{\pm}5^{\circ}C\;and\;810{\pm}5^{\circ}C$ respectively. FE-SEM analysis revealed that diameters of the silicon nanowires are $50{\sim}60nm$ with the length of several ${\mu}m$. XRD analysis showed that the growth direction of the nanowires is Si[111]. Field emission characteristics showed that the turn-of voltages at the current of $0.01\;mA/cm^{2}$ are $10\;V/{\mu}m\;and\;8.5\;V/{\mu}m$ for the wires grown at $700{\pm}5^{\circ}C\;and\;810{\pm}5^{\circ}C$, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.369.2-369.2
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• 2014

Diamond-like Carbon(DLC) films doping Si were deposited by linear ion source(LIS)-physical vapor deposition method on Si wafer. We have studied the effects of Si content on friction and wear properties of DLC films and the characteristics of the films were investigated using Nano-indentation, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS). The films has been various low-friction and low-stress by varying the flow rates of silane gas. Under the about 2% of Si doping is very suitable for improving the adhesion of films and reducing internal stress while maintaining the surfaces hardness of DLC films. Linear ion source (LIS)를 사용하여 Si wafer위에 Si 이온이 첨가된 DLC 박막을 증착하였다. 참가된Si 이온의 양에 따라 DLC 박막에 미치는 영향을 분석하기 위하여 마찰 계수 및 경도를 비교하였고, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS)를 통하여 표면 상태를 분석하였다. 천체 주입된 가스량의 약 2%까지 Si 이온 주입이 늘어날수록 DLC 박막의 마찰계수는 낮아졌고, 경도는 Si 이온이 주입되지 않았을 경우와 비슷한 값(약 20~23 GPa)을 가졌다. 2% 이상의 주입량에서는 마찰계수는 주입량이 늘어날수록 높아졌으며 경도는 떨어지는 경향을 보였다. 이는 Si이온이 2%이하로 첨가되었을 경우, DLC 박막의 생성시 탄소 이온들의 결합 Stress를 줄여 마찰계수가 줄어든다고 볼 수 있으며, 그 양이 2%이상이 되면 오히려 불순물로 작용하여 DLC 박막의 Stress는 급격히 증가하고 마찰계수도 높아짐을 알 수 있다.