• Journal of Powder Materials
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• v.4 no.4
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• pp.268-274
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• 1997

Characteristics of plasma nitriding and nitrocarburizing for steam treated sintered steels were studied. Fe-0.8%C powder containing Ni, Cu were sintered at 112$0^{\circ}C$ and steamed at 52$0^{\circ}C$. Temperature of plasma nitriding and nitrocarburizing was varied from 50$0^{\circ}C$ to $600^{\circ}C$. Gas mixture of nitriding was set at $N_2$ : $H_2$ =80:20 (vol.%), but $CH_4gas$ was added 1~2 vol.% for nitrocarburizing. Steam treatment for sintered steels brought not only the formation of oxide layer but also decarburizing near the surface. Decrease in hardness near the surface resulted from the formation of ferrite due to decarburizing. Thus, the low hardness was recovered not with plasma nitriding but with plasma nitrocarburixing. Wear resistance properties of steamed specimens and ni-trocarburized specimens were better than those of nitrided specimens according to the pin-on-disk wear test. On the other hand, the fatigue life of steamed specimen was shorter than that of nitrocaiburized specimen.

• Journal of Powder Materials
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• v.11 no.1
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• pp.69-73
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• 2004

The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1034-1037
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• 2002

In this study, we fabricated red organic electrolu-minescent device with a doping material (DCJTB), and The cell structure used ITO:indium tin oxide $[20{\Omega}]$/CuPc:Hole injection layer 20nm/NPB: Hole transfer layer 40nm/$Alq_3$ (host) + DCJTB(1% or 3%) (guest) Emitting layer 40nm/$Alq_3$ : Electron transfer layer 30nm/Al :Cathode layer 150nm. the luminescent layer consisted of a host material. 8-hydrozyquinoline aluminum $(Alq_3)$, and DCJTB dye as the dopant. a stable red emission (chromaticity coordinates : x=0.64, y=0.36) was obtained in this cell with the luminance range of $100-600cd/m^2$. we study the electrical and optical properties of devices.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.247-247
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• 2006

Chemical and physical synthesis routes were combined to prepare macroporous thin films of semiconducting metal-oxides such as $CaCu_{3}Ti_{4}O_{12}\;and\;TiO_{2}$ by sputtering onto (PMMA) microsphere templated substrates. Subsequently, the colloidal templates were removed by thermal decomposition. The remaining inorganic films comprised a monolayer of hollow hemispheres with diameter commensurate with that of the microspheres. This unique morphology increases the surface area and reduces the interfacial area between film and substrate. Consequently, the surface activity is markedly enhanced while deleterious interfacial effects between film and substrate are significantly reduced. Both effects are highly advantageous for gas sensing applications.

• Journal of Magnetics
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• v.11 no.4
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• pp.160-163
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• 2006

We have prepared crystalline Ag nanoparticles with an average size of 4 nm in diameter by using an inductively coupled plasma reactor equipped with the liquid nitrogen cooling system. Our magnetic data show that the nano-sized effect of Ag nanoparticles on the magnetic properties is ferromagnetic, instead of a diamagnetic component of the Ag bulk and a superparamagnetic component of magnetic nanoparticles. We have also studied the magnetic properties of Ag-Cu nanocomposites with an opposite concentration profile between surface and core. These comparisons indicate that the ferromagnetic component strongly depends on the surface of Ag nanoparticles, while the paramagnetic component is strongly affected by the outer oxide layer, with the background of a diamagnetic component from the core of Ag.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.10-13
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• 1999

For large scale applications of high temperature superconductor(HTS) such as transmission cables, motors and generators, long length of flexible HTS conductors is required. Currently, HTS tape that is capable of being fabricated in long length by industrial processes is the Bi-2223 HTS tape. In this study, we fabricated 19 filamentary Bi-2223($Bi_{1.8}$$Pb_{0.4}$$Sr_{2}$$Ca_{2}$$Cu_{3}$$O_{10+X}$) HTS tape with 100m length by PIT(Powder In Tube) process. Critical current(Ic) of this long length tape was measured 18.5 A at 77 K, self field and short sample Ic is 32.5 A at the same condition. Critical current of 100m length tape was decreased by about 1/3 compared to that of short tape. This was mainly resulted from the increase of non homogeneity in oxide layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1440-1442
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• 2005

We have fabricated vertical type organic thin film transistors (OTFTs) using organic semiconductor materials such as F16CuPc, NTCDA, PTCDI C-8 and C60. The layers of OTFT were fabricated by vacuum evaporation technique and spin casting method onto the Indium Tin Oxide (ITO) coated glass. I-V characteristics and on-off ratios of the fabricated OTFTs were investigated. In addition, we have fabricated light emitting transistor using MEH-PPV and then investigated EL electroluminescent properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.984-987
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• 2003

유기발광소자 안에 존재하는 비발광영역(dark spot)의 전압에 대한 영향을 근접장 마이크로파 현미경(near-field scanning microwave microscope)을 이용하여 관찰하였다. 유기발광소자는 glass/indiumtin oxide(ITO)/Cu-Pc/tris-(8-hydroquinoline)aluminum(Alq3)/aluminum(Al) 의 기본구조로 제작하였다. Dark spot은 ITO 기판을 부분적으로 에칭하여서 형성시켰다. Dark spot에 $0{\sim}l5 V$ 까지 전압을 인가시키면서 인가 전압에 따른 전기적 특성을 근접장 마이크로파 현미경 image의 변화와 반사계수인 $S_{11}$ 측정을 통하여 연구하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1270-1273
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• 2004

The combination of methane-chemical activation and Self-propagating High-temperature synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d < $1{\mu}m$ is developed. The specific feature of the technique is formation of the $YBa_2Cu_3O_{7-x}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.981-984
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• 2004

유기 발광소자(OLED)Glass/indium-tin-oxide(ITO)/Cu-Pc(copper-phthalocyanine)N,N'-Bis(3-methylphenyl)-1,1'-biphenylbenzidineltris-(8-hydroquinoline) aluminum(Alq3)/aluminum(Al)의 기본구조로 제작된 OLED에 다양한 전압을 인가하면서, 마이크로파 근접장 현미경을 이용하여 시간에 따른 소자의 전류-전압특성을 측정함으로써 전기적 전도 특성을 연구하였다. 또한 다양한 인가전압의 시간에 따른 EL(electro luminance)을 측정하여 소자의 광학적 특성과 전기적 특성을 연구 비교하였다.