• Corrosion Science and Technology
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• v.22 no.4
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• pp.221-231
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• 2023

Interest in aluminum alloys for the hydrogen valves of fuel cell electric vehicles (FCEVs) is growing due to the reduction in fuel efficiency by the high weight. However, when an aluminum alloy is used, deterioration in mechanical characteristics caused by hydrogen embrittlement and wear is regarded as a problem. In this investigation, the aluminum alloy used to prevent hydrogen embrittlement was subjected to surface treatments by performing hard anodizing and plasma ion nitriding processes. The hard anodized Al alloy exhibited brittleness in which the mechanical characteristics rapidly deteriorated due to porosity and defects of surface, resulting in a decrease in the ultimate tensile strength and modulus of toughness by 15.58 and 42.51%, respectively, as the hydrogen charging time increased from 0 to 96 hours. In contrast, no distinct nitriding layer in the plasma ion-nitrided Al alloy was observed due to oxide film formation and processing conditions. However, compared to 0 and 96 hours of hydrogen charging time, the ultimate tensile strength and modulus of toughness decreased by 7.54 and 13.32%, respectively, presenting excellent resistance to hydrogen embrittlement.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.309-314
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• 2023

This study aimed to address the limitations of traditional plasma nitriding methods by implementing a short-term plasma oxy-nitriding treatment on the surface of AISI 420 martensitic stainless steel. This treatment involved the sequential formation of nitride and oxide layers, to enhance surface hardness and corrosion resistance, respectively. The process resulted in the formation of a 20 ㎛-thick nitride layer and a 3 ㎛-thick oxide layer on the steel surface. Initially, the hardness increased by 2.2 times after nitriding, followed by a subsequent decrease of approximately 31 % after oxidation. While the nitriding process reduced corrosion resistance, the subsequent oxidation process led to the formation of a passive oxide film, effectively resolving this issue. The pitting corrosion of the oxide passive film started at 82.6 mVssc, providing better corrosion resistance characteristics than the nitride layer. Consequently, the trade-off between surface hardness and corrosion resistance in plasma oxy-nitrided AISI 420 martensitic stainless steel is anticipated to be recognized as an innovative and comprehensive surface treatment process for biomedical components.

• Journal of Surface Science and Engineering
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• v.56 no.5
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• pp.328-334
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• 2023

The carbon-based films have various properties, which have been widely applied in industrial application. However, it has critical drawback for poor adhesion between films and metal substrate. In the present work, we have deposited carbon-based films on injection mold steel by plasma assisted chemical vapor deposition (PACVD). In order to improve adhesion, prior to film deposition, the substrate was nitriding-treated using PACVD. And its effect on the adhesion was investigated. Due to the pre-nitriding, the amorphous carbon nitride (a-CN:H) films presented 10 times higher adhesion (34.9 N) than that of un-nitirided. In addition, a friction coefficient was decreased from 0.29 to 0.15 for the amorphous carbon (a-C:H) due to improved adhesion. The obtained results demonstrated that pre-nitriding considerably improved the adhesion, and the relationship among adhesion, hardness, and surface roughness was discussed in detail.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.443-450
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• 1993

Self-alignment gatc Schottky contact structure on Si- implanted GaAs was formed by plasma enhanced chemical vapor dcposirion. Tungsten nitride thin films (ahclut 1600$\AA$) \vcre dopositcd on GaAs at $350^{\circ}C$ in order to fahricarc GaAs 1Cs and ttwn rapidly annealed at $750^{\circ}C$ to $900^{\circ}C$. Thermal charac tcristics of PECVD)-$W_{67}N_{43}$/GaAs structure were investigated by X-ray diffraction, photolumintesccnce. and optical deep level transient specrroscopy. Results revealed that $W_{67}N_{33}$ gate was more thermally sta ble with GaAs substrate than W gate and Si atoms implanted In $W_{67}N_{33}$/GaAs structure became morr active than those In W/GaAs after annealing. I-V characteristics of $W_{67}N_{33}$/GaAs diod c exhibired a nearly ideal diode behavior. The termal stability of $W_{67}N_{33}$/GaAs diode was better than that of W/GaAs diode with the post annealing at temperatures from 800 to $900^{\circ}C$ for 20s without As overpressure.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.212-217
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• 2000

Dielectric thin films for TFT(thin film transistor)s, such as silicon nitride$(Si_3N_4)$ and silicon oxide$(SiO_2)$, are usually deposited at $200~300^{\circ}C$. In this study, authors have tried to form dielectric films not by deposition but by oxidation with ECR(Electron Cyclotron Resonance) oxygen plasma, to improve the interface properties was not intensionally heated during oxidation. THe oxidation was performed consecutively without breaking vacuum after the deposition of a-Si: H films on the substrate to prevent the introduction of impurities. In this study, especially pulse mode of microwave power has been firstly tried during FCR oxygen plasma formation. Compared with the case of the continuous wave mode, the oxidation with the pulsed ECR results in higher quality silicon oxide$SiO_X$ films in terms of stoichiometry of bonding, dielectric constants and surface roughness. Especially the surface roughness of the pulsed ECR oxide films dramatically decreased to one-third of that of the continuous wave mode cases.

• Korean Chemical Engineering Research
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• v.47 no.2
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• pp.150-156
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• 2009

Plasma Display Panels(PDPs) require to have improved luminous efficiency, low manufacturing cost, and high image quality to compete with other flat display devices such as Liquid Crystal Displays(LCDs) and organic light-emitting diodes(OLEDs). In addition, the diversity of product line-up may be needed for high market share. In this paper, the optical characteristics of typical green phosphor for PDP application are reviewed and the problem-based solution will be proposed. We also shortly describe the principle of 3D-PDPs which are promising. Then, the requirement of green phosphor for 3D-PDP application is summarized and research achievement, as of now, is described. The typical problems of $Zn_2SiO_4:Mn$ phosphor, which is the most well-known, are the negatively charged surface property and the long decay time, which leads to unstable discharge in green cell and afterimage. These problems were solved by coating the phosphor surface with metallic oxide. It was found that $Al_2O_3$ would be the best material for $Zn_2SiO_4:Mn$ phosphor. It gives longevity as well as low operating voltage due to the charging effect in green cells. Also, new phosphors, $(Y,\;Gd)Al_3(BO_3)_4:Tb$ and $(Mg,\;Zn)Al_2O_4:Mn$ phosphor are proposed for increasing the luminance and reducing the decay time, which are capable to apply for 3D-PDP application.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.148-148
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• 1999

다이아몬드에 버금가는 높은 경도뿐만 아니라 높은 화학적 안정성 및 열전도성 등 우수한 물리화학적 특성을 가진 입방정 질화붕소(cubic Boron Nitride)는 마찰.마모, 전자, 광학 등의 여러 분야에서의 산업적 응용이 크게 기대되는 자료이다. 특히 탄화물형성원소에 대해 안정하여 철계금속의 가공을 위한 공구재료로의 응용 또한 기대되는 재료이다. 특히 탄화물형성원소에 대해 안정하여 철계금속의 가공을 위한 공구재료로의 응용 또한 크게 기대된다. 이 때문에 각종의 PVD, CVD 공정을 이용하여 c-BN 박막의 합성에 대한 연구가 광범위하게 진행되어 많은 성공사례들이 보고되고 있다. 그러나 이러한 c-BN 박막의 유용성에도 불구하고 아직 실제적인 응용이 이루어지지 못한 것은 증착직후 급격한 박리현상을 보이는 c-BN 박막의 밀착력문제때문이다. 본 연구에서는 평행자기장을 부가한 ME-ARE(Magnetically Enhanced Activated Reactive Evaporation)법을 이용하여 c-BN 박막을 합성하고, 합성된 c-BN 박막의 밀착력에 미치는 공정인자의 영향을 규명하여, 급격한 박리현상을 보이는 c-BN 박막의 밀착력 향상을 위한 최적 공정을 도출하고자 하였다. BN 박막 합성은 전자총에 의해 증발된 보론과 (질소+아르곤) 플라즈마의 활성화반응증착(activated reactive evaporation)에 의해 이루어졌다. 기존의 ARE장치와 달리 열음극(hot cathode)과 양극(anode)사이에 평행자기장을 부여하여 플라즈마를 증대시켜 반응효율을 높혔다. 합성실험용 모재로는 p-type으로 도핑된 (100) Si웨이퍼를 30$\times$40 mm크기로 절단 후, 100%로 희석된 완충불산용액에 10분간 침적하여 표면의 산화층을 제거한후 사용하였다. c-BN 박막을 얻기 위한 주요공정변수는 기판바이어스 전압, discharge 전류, Ar/N가스유량비이었다. 증착공정 인자들을 변화시켜 다양한 조건에서 c-BN 박막의 합성하여 밀착력 변화를 조사하였다. 합성된 박막의 결정성 분석을 FTIR을 이용하였으며, Bn 박막의 상 및 미세구조관찰을 위해 투과전자현미경(TEM;Philips EM400T) 분석을 병행하였고, 박막의 기계적 물성 평가를 위해 미소경도를 측정하였다. 증착된 c-BN 박막은 3~10 GPa의 큰 잔류응력으로 인해 증착직후 급격한 박리현상을 보였다. 이의 개선을 위해 증착중 기판바이어스 제어 및 후열처리를 통해 밀착력을 수~수백배 향상시킬 수 있었다. c-BN 박막의 합성을 위해서는 증착중인 박막표면으로 큰 에너지를 갖는 이온의 충돌이 필요하기 때문에 기판 바이어스가 요구되는데, c-BN의 합성단계를 핵생성 단계와 성장 단계로 구분하여 인가한 기판바이어스를 달리하였다. 이 결과 그림 1에서 나타낸 것처럼 c-BN 박막의 핵생성에 필요한 기판바이어스의 50% 정도만을 인가하였을 때 잔류응력은 크게 경감되었으며, 밀착력이 크게 향상되었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.06a
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• pp.8-8
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• 2001

초고속 증착은 짧은 시간에 박막 형성을 가능하게 하므로 window glass 코팅등의 대면적 코팅에 있어서 비용을 절감 시키고, 대량생산을 가능하게 만들기 때문에 관심이 집중되고 있다. 고속증착 공정으로는 high current arc, laser arc, hollow cathode discharge ion plating 그리고 마그네트론 스퍼터링법 등이 있다. 특별히 마그네트론 스퍼터링법은 3m이상의 넓이에 코팅을 할때 두께가 매우 균일하며, 증착율은 evaporation 공정에 비해 경제적, 기능적인 면에서 효율적이다. 그리고 증착된 박막은 매우 조밀하고 좋은 밀착력을 갖고 있으며, 고융점 금속을 포함하여 금속 합금 및 혼합물의 비율을 조정 및 금속 산화물, 질화물, 탄화물 등과 같은 금속의 증착도 stoichiometry를 조정하여 박막을 합성 시키는데 있어서 효과적이다. 이러한 초고속 증착을 만들기 위한 마그네트론 스퍼터링법의 요건은 마그네트론 원이 높은 타켓 power density를 가져야 하며, 타켓에서 효율적으로 플라즈마를 구속하여 스퍼터 되는 이온의 양을 최대화 시킬 수 있어 한다. 따라서 본 실험에서는 초고속 증착을 위해서 직경 50mm 타켓의 UBM magnetron원을 설계 제작하였다. 고밀도의 플라즈마를 형성시키기 위해서, Poisson simulation c code를 이용하여 자기장의 방향, 세기 및 밀도를 측정 하였고, 자기장 측정기(Gauss meter)를 이용하여 실제 자장을 측정 비교 분석하였다. 상기의 data를 바탕으로 여러 형상의 마그네트론원을 설계, 제작하였고. 마그네트론 원의 특성 분석을 위해 I-V 방전 특성을 평가하였고 substrate ion current density와 박막의 증착율을 측정하였다.duty-on 시간의 증가에 따라 $Cr_2N$ 상의 형성이 점점 많아져 80% duty-on 시간 경우에는 거의 CrN과 $Cr_2N$ 상이 공존하는 것으로 나타났다. 또한 duty-on 시간이 증가할수록 회절피크의 세기가 증가하여 결정화가 더 많이 진행되어짐을 알 수 있었다. 마찬가지로 바이어스 펄스이 주파수에 다른 결정성의 변화도 펄스의 주파수가 증가할수록 박막이 결정성이 좋아지고 $Cr_2N$ 상이 쉽게 형성되었다. 증착 진공도에 따른 결정성은 상대적으로 질소의 농도가 높은 낮은 진공도에서는 CrN 상이 주로 형성되었으며, 반대로 높은 진공도에서는 $Cr_2N$ 상이 많이 만들어졌다. 즉 $1.3{\times}10^{-2}Torr$의 증착 진공도에서는 CrN 상만이 보이는 반면 $9.0{\tiems}1-^{-2}Torr$ 진공도에서부터 $Cr_2N$ 상이 형성되기 시작하여 $5.0{\tiems}10^{-2}Torr$ 진공도에서는 두개의 상이 혼재되어 있음을 알 수 있었다. 박막의 내마모성을 조사한 결과 CrN 박막의 마찰 계수는 초기에 급격하게 증가한 후 0.5에서 0.6 사이의 값으로 큰 변화를 보이지 않았으며, $Cr_2N$ 박막도 비슷한 거동을 보였다.차 이, 목적의 차이, 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lrcorner$

• Journal of the Korean Society for Heat Treatment
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• v.11 no.2
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• pp.99-110
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• 1998

The effects of pre-heat treatment(Q/T) on microstructure and hardness of SCM435 structural steel nitrided by micro-pulse plasma was investigated. The quenching and tempering temperatures for obtaining matrix hardness of SCM435 steel on range of HRC30 to HRC40 desired for machine parts were about $860^{\circ}C$ and $500^{\circ}C$ respectively. The case depth of SCM435 nitrided at $480^{\circ}C$ for 5 hours was independent of pre-heat treatment condition and was approximately $150{\mu}m$. However, hardness and compactness of nitrified layer on Q/T treated specimen were more heigher than annealed specimen. The case depth increased linearly with the increase of nitriding temperature, however, the hardness of nitrified layer decreased with the temperature. Phase mixture of ${\gamma}^{\prime}$-phase($Fe_4N$) and ${\varepsilon}$-phase($Fe_3N$) were detected by XRD analysis in the nitrified layer formed at optimum nitriding condition, and only single ${\gamma}^{\prime}$-phase was detected in the nitrified layer formed at higher nitriding temperature such as $540^{\circ}C$. The optimum nitriding temperature was approximately $480^{\circ}C$ which is lower than tempering temperature for preventing softening behavior of SCM435 matrix during nitriding process and the surface hardness of nitrified layer obtained by optimum preheat treatment condition was about Hv930.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.2
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• pp.106-112
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• 2010

In order to compete with other flat display devices such as Liquid Crystal Displays (LCDs) and organic light emitting diodes (OLEDs), Plasma Display Panels (PDPs) require to have high performances like high image quality, low power consumption and high speed driving. In this paper, Fe doped MgO protective layer was introduced for higher performance. Both the surface characteristics of the deposited thin films and the electro-optical properties of 4 inch test panels were investigated. It has been demonstrated experimentally that ac PDP with Fe doped MgO protective layer has lower discharge voltage than that of undoped MgO film, which corresponds to measured secondary electron emission coefficients. The crystallinity and surface roughness of thin films were determined by XRD patterns and AFM images. In addition, ac PDP with Fe doped MgO protective layer has improved address discharge time lag for high speed driving.