• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.311-314
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• 2005

We investigated the composition dependence of the tunneling magnetoresistance (TMR) behavior and the stability of the magnetic tunnel junctions (MTJs) with TiAlOx barrier and the microstructural evolution of TiAl alloy films. The TMR ratio increased up to $49\%$ at $5.33\;at\%$ Ti. In addition, a significant tunneling magnetoresistance (TMR) value of $20\%$ was maintained after annealing at $450^{\circ}C$, and the breakdown voltage ($V_B$) of and 1.35 V were obtained in the MTJ with $5.33\;at\%$ Ti-alloyed AlOx barrier. These results were closely related to the enhanced quality of the barrier material microstructure in the pre-oxidation state. Ti alloying enhanced the barrier/electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal and electrical stability of the MTJs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.111-115
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• 2003

200nm 정도의 두께를 가진 SBT 박막이 liquid delivery MOCVD 공정에 의해 (111) oriented Pt/Ti/$SiO_2$/Si 기판 위에 증착되었다 이 실험에서는 $Sr(TMHD)_2$tetraglyme, $Bi(ph)_3$ 그리고 $Ta(O^iPr)_4$(TMHD)를 출발 물질로 사용하였다. Sr 출발 물질의 열적 안정화를 위해서 adduct로 tetraglyme를 사용하여 실험하였고 유기 용매로는 n-butyl acetate를 사용하였다 Substrate temperature와 reactor pressure는 각각 $570^{\circ}C$와 5Torr로 유지시켰다. 또한 vaporizer의 용도는 $190-200^{\circ}C$, 그리고 delivery line 의 온도는 vaporizer 보다 높게 유지 $(220-230^{\circ}C)$하여 출발 용액을 분당 0.1ml로 50분간 주입하였다. 수송가스로 Ar, 산화제로 $O_2$ 가스를 사용하였다. 제조한 SBT 박막은 $750^{\circ}C$에서 열처리한 후 인가전압 3V와 5V에서 $2P_r$값이 각각 6.47, $8.98{\mu}C/cm^2$이었으며, $2E_c$값은 인가전압 3V와 5V에서 각각 2.05, 2.31V이었다 그리고 $800^{\circ}C$에서는$750^{\circ}C$에서 열처리한 SBT 박막보다 다소 우수한 이력특성을 나타내어 $2P_r$ 값은 인가전압 3V와 5V에서 각각 7.59, $10.18{\mu}C/cm^2$ 이었으며, $2E_c$값은 인가 전압 3V와 5V에서 각각 2.00, 2.21V 이었다.

• Journal of Sensor Science and Technology
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• v.8 no.3
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• pp.274-282
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• 1999

The In doped ZnO(ZnO:In)thin films sensitive to $NH_3$ gas were prepared by the double layer depositions of In film by vacuum evaporation and ZnO film by rf magnetron sputtering method onto a $SiO_2$/Si wafer substrate, and subsequent heat treatment process. The structural and electrical characteristics of the ZnO:In thin films were studied as a function of heat treatment temperature by x-ray diffraction, scanning electron microscope and 4 point probing method. And the dependence of the sensitivity, the selectivity and the time response of the thin films on heat treatment temperature was investigated. The thin film heat-treated at $400^{\circ}C$ showed the highest sensitivity of 140% at an operating temperature of $300^{\circ}C$. The sensitivity towards CO, $NO_x$, gases observed in the same temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.1
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• pp.1-9
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• 2007

The performance of the small scale cyclone incinerate system (100kg/hr) to process the sewage sludge containing high moisture is evaluated. The incinerate system design is based on properties of the domestic sewage sludge. The combustion characteristics of the incinerate system is tested and analyzed with the various operation conditions of the moisture level, the sludge feed rate and the auxiliary fuel feed rate. The pressure loss of the whole system is appeared relatively small of 700mmAq under the normal operating condition and the temperature distribution of the incinerator internal combustion is maintained less than 1000C. Auxiliary fuel of 4.7 1/hr is required to incinerate 100kg sludge which include 87% moisture. Because the inside temperature of the incinerator is maintained less than $1000^{\circ}C$, it is predicted that the most NOx measured is produced not from the heat during the combustion process but from the oxidation of the N ingredient in the sludge. From the component analysis of ash, the organic matter is not entirely detected. Accordingly, it is estimated that the complete combustion has been accomplished in the incinerator.

• Journal of the Korean Institute of Gas
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• v.18 no.5
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• pp.33-39
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• 2014

Heat transfer oils are used in applications such as chemical plant heating systems, refinery heat exchange systems, certain gas processes, injection molding systems, and pulp and paper processing. These oils are extremely stable and resistant to thermal and oxidative degradation. In the event of a spill or accidental release of heat transfer oils, it can be ignited easily when there is an ignition source. This study discusses the status of safety management through the actual status of the heat transfer oils to prevent fire and explosion accidents in industries for process safety management. The actual status of the heat transfer oils in process system of industries surveyed by a questionnaire developed. The results of this study can be used to help establishment of safety management to prevent fire and explosion accidents, such as the management of heat transfer oils, safe operation and maintenance in heat transfer oil processes.

• Membrane Journal
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• v.22 no.1
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• pp.35-45
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• 2012

We prepared the highly ordered nano-wires of polypyrrole, polyaniline conductive polymers and polypyrrole/ polyaniline conductive copolymers by templating the anodic aluminum oxide (AAO) porous membrane, in which pore diameter was 20 nm, 100 nm and 200 nm. Those conductive polymers were grown from pore inner surface of AAO membrane forming hollow tubes and then wire structures were formed after 3 hour polymerization. By removing AAO membrane templates using sodium hydroxide solution, the conductive polymer nano-wires were successfully obtained, of which diameter and length were close to the ones of nano-pores in AAO membrane template. Crystallinity and thermal stability of the conductive polymer nano-wires were higher than irregular ones that prepared by solution polymerization. Furthermore, the electrical resistance of conductive polymer nano-wires were reduced by about 4~60% compared with that of the irregular polymers prepared by solution polymerization.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.72-72
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• 2010

탄소나노튜브(carbon nanotubes : CNTs)는 뛰어난 전기적, 물리적인 특성을 가지고 있기 때문에 다양한 분야에서 이를 활용하려는 노력들이 활발히 이루어지고 있다. CNTs의 전기적인 특성은 직경에 의해 결정되므로, 직경을 균일하게 제어하는 일이 CNTs를 기반으로 한 전자소자 응용에 가장 중요한 사항이라 할 수 있다. 일반적으로 화학기상증착법(chemical vapor deposition, CVD)으로 합성된 CNTs의 직경은 촉매의 크기에 의존하기 때문에, 촉매의 크기를 제어하기 위한 다양한 연구들이 활발히 진행되고 있다[1-3]. 하지만 CNTs의 성장온도 근처에서 촉매 입자는 표면 확산(surface diffusion)에 의해 응집(agglomeration)되기 때문에 작고 균일한 크기의 촉매를 얻기 어렵다. 본 연구에서는 Si(001) 기판 위에 지지층(supporting layer)인 Al의 두께를 변화시켜 증착하고, 열적산화과정을 통해 $Al_2O_3$ 층을 형성한 후 Fe을 증착하여 CNTs를 합성하였다. $Al_2O_3$ 지지층과 Fe 촉매입자의 구조와 화학적 상태를 원자힘현미경 (atomic force microscopy, AFM), 주사전자현미경 (scanning electron microscopy, SEM), 투과전자현미경 (transmission electron microscopy, TEM), X-선 광전자 분광기(X-ray photoelectron spectroscopy)를 통해 분석하였고, 성장된 CNTs는 SEM, TEM, 라만 분광법 (Raman spectroscopy)을 통해 분석하였다. 그 결과, $Al_2O_3$ 층은 두께에 따라 각기 다른 표면 거칠기(RMS roughness)와 결정립(grain)의 크기를 갖게 되며, 이러한 표면구조가 Fe 촉매입자의 표면확산에 의한 응집에 관여하여 CNTs의 직경에 영향을 미치는 것을 확인하였다. 또한 $Al_2O_3$ 지지층의 두께가 15 nm인 경우, Fe의 응집현상이 억제되어 좁은 직경분포를 지닌 고순도 단일벽 탄소나노튜브(Single-walled CNTs)가 성장되는 것을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.106-106
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• 2010

CuO 나노입자는 전기화학적 전지, 가스 센서 및 태양전지와 같은 나노 전자소자에 응용할 수 있는 대단히 유용한 물질이다. CuO 나노구조를 형성하기 위한 방법은 솔-겔법, 전기 화학적 방법 및 전구체의 열적 탈착방법 등으로 연구되어 왔으나 CuO 나노입자의 열처리 효과는 상대적으로 연구가 미흡하다. 본 연구에서는 $Al_2O_3$ 기판 위에 스핀 코팅법과 열처리를 사용하여 형성한 CuO 나노입자의 물리적 성질을 살펴보았다. CuO 나노 입자를 형성하기 위해 methanol에 Cu(I) acetate (5 wt%) 을 적절히 분산한 용액을 $Al_2O_3$ 기판 위에 7000 rpm으로 스핀 코팅을 한 후 $300^{\circ}C$, $500^{\circ}C$ 및 $700^{\circ}C$로 각각 1 시간 동안 산소 분위기에서 열처리를 하였다. X-선 회절법 결과는 CuO의 (200)$K_{\alpha}$와 (400) $K_{\alpha}$ 회절에 해당하는 피크가 나타났고 주사 전자현미경 상의 결과는 CuO 나노입자가 형성되었음을 확인하였다. 나노입자의 크기는 고배율 투과 전자현미경상에 의하여 3-5 nm 인 것으로 확인하였고 300 K에서 측정한 광루미네선스 스펙트럼은 CuO의 주된 스펙트럼 피크가 푸른색 영역에서 나타남을 알 수 있었다. X-선 광전자 분광법 스펙트럼은 Cu $2p_{3/2}$와 O 1s의 전자상태를 보여주었으며 복잡한 산화상태를 갖는 CuO는 Cu-O 결합과 산소의 화학적 흡착상태를 가지는 것으로 확인되었다. 이러한 결과는 $Al_2O_3$ 기판 위에 최적화된 CuO 나노 입자의 형성 방법과 구조적, 광학적 및 전자적 특성을 이해하는데 도움을 제공해 줄 것이다.

• Polymer(Korea)
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• v.35 no.6
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• pp.526-530
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• 2011

Furan-2,5-dicarboxylic acid (FDCA) was synthesized by $KMnO_4$ oxidation of 2,5-dihydroxymethylfuran(DHMF) derived from biomass. Polyesters were synthesized by esterification and polycondensation of FDCA with various diols(ethane-1,2-diol, propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol, decane-1,10-diol). The composition of polyesters was characterized by using $^1H$ NMR. Thermal properties of the polyesters were characterized by DSC and TGA. Intrinsic viscosities(IV) of the polyesters were measured to be 0.78~1.2 dL/g comparable with IV of commercial poly(ethylene terephthalate)(PET). As the chain lengths of diols increased, Young's modulus and strength decreased and elongation-to-break generally increased. Young's modulus and strength of the polyesters were measured to be 3551 MPa and 103 MPa, respectively, comparable with commercial PET.

• Composites Research
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• v.34 no.2
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• pp.108-114
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• 2021

Graphene flakes are generally mass-produced by converting graphene oxide into reduced graphene oxide using chemical or thermal reduction. These graphene flakes can be stacked to form a free-standing graphene paper, which can be used for various applications. However, a graphene paper lacks stretchability, which hinders its application in stretchable devices. In this work, we introduced wrinkles in a graphene paper to make it stretchable. A graphene paper fabricated by vacuum-filtering a graphene dispersion was placed on a pre-stretched adhesive film. When the pre-stretched adhesive film returned to the original state, the graphene paper was wrinkled. The effect of the pre-stretching and wet condition of the graphene papers was experimentally investigated by using scanning electron microscopy. In addition, we observed the change of the period of the wrinkles in the graphene paper depending on the pre-stretching.