• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1802-1806
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• 2007

Nowadays, many configurations and applications of small atmospheric plasma source have been investigated with growing interest, as it provides the bacteria inactivation, the surface modification and removal of unwanted small regions, and so on. In this paper, the non-thermal micro plasma source under atmospheric pressure by means of submicrosecond pulse voltage waveforms is suggested. Plasma operates in helium is appears as a small (sub-mm) glow at the tip of a plasma gun. Electrical measurements show that the plasma source operates at low voltage (about 500V) and the power consumption is about 1W at 25kHz. Moreover, the emission spectrum shows the relatively higher emission intensity of oxygen particles than those of helium and nitrogen.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.5
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• pp.717-720
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• 2012

Various types of dielectric-barrier-discharge (DBD) devices have been developed for diverse applications for the last decade. In this study, a flat non-thermal DBD micro plasma source under atmospheric pressure has been developed. The flat-panel type plasma is generated by bipolar pulse voltages, and driving gas is air. In this study, the plasma source was investigated with intensified charge coupled device (ICCD) images and Optical Emission Spectroscopy (OES). The micro discharges are generated on the crossed electrodes. For theoretical analysis, 2-dimensional fluid simulation was performed. The plasma source can be driven in air, and thus the operation cost is low and the range of application is wide.

• Journal of the Korean institute of surface engineering
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• v.45 no.2
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• pp.53-60
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• 2012

Modulated Pulse Power (MPP) magnetron sputtering is a new high-power pulsed magnetron sputtering (HPPMS) technology which overcomes the low deposition rate problem by modulating the pulse voltage shape, amplitude, and the duration. Highly ionized magnetron sputtering can be performed without arcing because it can be controlled as multiple steps of micro pulses within one overall pulse period in the range of 500-3,000 ${\mu}s$. In this study, the various waveforms of discharge voltage and current for micro pulse sets of MPP were investigated to find the possibility of controlling the strongly ionized plasma mode. Enhanced ionization of the sputtered metal atoms was obtained by OES. Large grained columnar structure can be grown by the strongly ionized plasma mode in the AZO deposition using MPP. In the most highly ionized deposition condition, the preferred orientation of (002) plane decreased, and the resistivity, therefore, increased by the plasma damage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1218-1222
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• 2008

We investigate the effect of rise time of a pulse bias voltage on atmospheric plasma generation. With the faster rise time of the pulse bias, the glow discharge appears to be more uniformly generated along the electrodes. I-V measurement confirms that higher loading power can be obtained using the faster rise time. A new understanding for atmospheric plasma generation at a micro-gap electrode is suggested.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.117-128
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• 1999

This study was carried out to investigate the surface characteristics of SCM440 steel nitrided with various nitrogen contents for 7 hours at $520^{\circ}C$ by using micro-pulse plasma nitriding apparatus of hot wall type. The effects of oxidation treatment was also investigated on plasma nitrided in 30% nitrogen and post oxidized SCM440 steel at $500^{\circ}C$ in $H_2O$ atmosphere. The ${\gamma}^{\prime}-Fe_4N$ and ${\varepsilon}-Fe_{2-3}N$ phases were detected in compound layer of the nitrided steel. As the content of nitrogen in plasma gas increased with 30, 50, 70% on the micro-pulse plasma nitriding for SCM440 steel, the thickness of compound, diffusion layer and the surface hardness were increased. From the wear test results, the best wear resistance was appeared in the condition of ductile ${\gamma}^{\prime}-Fe_4N$ phase formed specimen at 30% nitrogen, whereas that of the treated with 50% and 70% nitrogen decreased owing to the exfoliation of brittle ${\varepsilon}-Fe_{2-3}N$ phase in the compound layer. On the nitrided and subsequently oxidized SCM440 steel, the surface layer consisted of $Fe_3O_4$, ${\gamma}^{\prime}-Fe_4N$, and ${\varepsilon}-Fe_{2-3}N$ phases. In these treatments, the dissolution of nitrides affect hardness and hardening depth in compound and diffusion layers. For the nitrided in 30% nitrogen and post oxidized specimen at $500^{\circ}C$ for 1 hour, the wear resistance was lower than that of the only nitrided one in 30% nitrogen but higher than those of the nitrided ones in 50 and 70% nitrogen.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.430-430
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• 2012

Modulated pulsed power (MPP) 스퍼터링은 펄스 전압 shape, amplitude, duration의 modulation을 통해 증착율 손실을 극복하는 고출력 펄스 마그네트론 스퍼터링의 한 종류이다. Micro second 범위에서 on/off 시간을 다중 세트 형태로 자유롭게 프로그램 할 수 있어서 아킹 없이 고전류 영역의 마그네트론 동작을 할 수 있으므로, 고주파 유도 결합 플라즈마원이나 마이크로웨이브 투입 등의 부가적인 플라즈마 없이도 스퍼터링 재료의 이온화 정도를 획기적으로 높일 수 있는 장점을 가지고 있다. 본 연구에서는 $2{\times}1{\times}0.2$의 sputtering system에서 기판 캐리어를 이용해서 $400{\times}400mm$ 기판을 $272{\times}500mm$ 크기의 AZO target (Al 2 wt%)이 설치되어 있는 moving magnet cathode (MMC)을 이용하여 MPP로 증착했다. 두 종류의 micro pulse set을 하나의 macro pulse에 사용함으로서 weakly ionized plasma와 strongly ionized plasma를 만들 수 있다. 다양한 micro pulse set을 이용하여 평균 전력 2 kW에서 peak 전력을 4 kW에서 45 kW까지 상승 시킬 수 있으며, 이 때 타겟-기판 거리 80 mm에서 이온전류밀도는 $5mA/cm^2$에서 $20mA/cm^2$까지 상승했다. MPP는 같은 평균 전력에서 repetition frequency가 증가할 때, 증착 속도가 증가했으며, 같은 repetition frequency에서 macro pulse length가 증가할 때도, 증착 속도가 증가했다. 최적화된 marco, micro pulse set에서 증착 속도는 평균 전력 2 kW에서 110 nm/min이었고, 700 nm의 박막에서 비저항은 $1-2{\times}10^{-3}ohm{\cdot}cm$였다. 표면거칠기 Rrms는 약 3 nm였고, 400-700 nm 영역의 평균 투과도는 72-76%였다.

• Journal of the Korean institute of surface engineering
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• v.55 no.5
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• pp.292-298
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• 2022

In this study, PEO (plasma electrolytic oxidation) film formation behavior of AZ31 Mg alloy under application of 300 Hz pulse current was studied by the analyses of V-t curve, arc generation behavior, PEO film thickness and morphology of PEO films with treatment time in 0.05 M NaOH + 0.05 M Na₂SiO₃ + 0.1 M NaF solution. PEO films was observed to grow after 10 s of application of pulse current together with generation of micro-arcs. PEO film grew linearly with treatment time at a growth rate of about 5.58 ㎛/min at 200 mA/cm² of pulse current but increasing rate of film formation voltage became lowered largely with increasing treatment time after passing about 250 V, suggesting that resistivity of PEO films during micro-arc generation decreases with increasing film formation voltage at more than 250 V.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1063-1067
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• 2001

The effect of the pulse parameters(pulse ratio and frequency) on the characteristics of the nitrided layer in the pulsed plasma nitrified SCM435 Steels was investigated. Material properties of the nitrided layer were analysed by employing optical microscope, scanning electron microscope(SEM), X-ray diffractometer(XRD) and micro-Vickers hardness tester. It was found that both the compound layer thickness and the surface hardness decreased with decreasing of pulse ratios. At high pulse ratio, the compound layer thickness and the surface hardness were rapidly decreased with decreasing frequency compared to lower pulse ratios.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.712-720
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• 1998

The effect of H2:N2 gas ratio on the case thickness hardness and nitrides formation in the sur-face of SCM440 machine structural steel have been studied by micro-pulse plasma process. The thickness of compound layer increased with the increase of nitrogen content in the gas com-position. The maximum thickness of compound layer the maximum case depth and the maximum surface hardness were about 15.8${\mu}m$, 400${\mu}m$ and Hv765 respectively in the nitriding condition of 250Pa and 70% nitrogen content at $520^{\circ}C$ for 7hrs. Generally only nitride phases such as ${\'{\gamma}}$($Fe_4N$)$\varepsilon(Fe_2}{_3N}$ phases were detected in compound and diffusion layer by XRD analysis. The amount of $\varepsilon(Fe_2}{_3N}$ phase increased with the increase of nitrogen content. The relative amounts and kind of phases formed in the nitrided case changed with the change of nitrogen content in the gas composition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.2
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• pp.65-69
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• 2014

Crystallographic phases of Plasma electrolytic oxidized Al alloy, A1100, A5052, A6061, A6063, A7075, were investigated. Two types of electrolyte $Na_2Si_2O_3$ and Na2P2O7 were also compared. Bipolar pulse, $2000{\mu}sec$ with $400{\mu}sec+420V$ impulse and $300{\mu}sec$ - impulse were applied for 20 min. ${\alpha}-alumina$, ${\gamma}-alumina$, ${\eta}-alumina$, $Al_{4.95}Si_{1.05}O_{9.52}$, and $(Al_{0.9}Cr_{0.1})_2O_3$ were mainly observed. Si, component of electrolyte, were moved into the PEO layer by bipolar pulse. Glassy phase was also observed at the surface of $Na_2Si_2O_3$ electrolyte treated PEO layer, and increased with the Mg content of Al alloy. It is concluded that at first glassy phase was formed by the micro plasma, and the high temperature of plasma turns glassy phase to several crystalline phases. And we could expect that many other crystalline phase could be formed by PEO process.