• Korean Journal of Materials Research
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• v.9 no.7
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• pp.735-739
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• 1999

In this study we investigated stress development and shrinkage of thickness for a single $PbTiO_3$(PT) layer prepared by sol-gel processing. Changes of microhardness for multideposited PT layers with temperatures are also monitored to understand the densification of thin films. Single PT layer shrank rapidly from room temperature to$ 220^{\circ}C$ yielding 83% of total shrinkage observed up to $500^{\circ}C$. A tensile stress of ~75MPa developed in an as-spun layer, and increased steadily beyond $130^{\circ}C$ until it reaches the maximum value of 147MPa at $250^{\circ}C$. The significant decrease of tensile stress in the film beyond $370^{\circ}C$ indicates that thermal expansion mismatch between the film and the substrate dominates the stress behavior in this temperature range. Microhardness of the multideposited coatings also increased rapidly above $300^{\circ}C$ regardless of the pyrolysis temperatures used. Large amount of perovskite phase formed in multideposited coatings after $550^{\circ}C$ may be due partly to enhanced homogeneous nucleation in the thicker coating.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.377-377
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• 2011

Organic solar cells (OSCs) with low cost have been studied to apply on flexible substrate by solution process in low temperature [1]. In previous researches, conventional organic solar cell was composed of metal oxide anode, buffer layer such as PEDOT:PSS, photoactive layer, and metal cathode with low work function. In this structure, indium tin oxide (ITO) and Al was generally used as metal oxide anode and metal cathode, respectively. However, they showed poor reliability, because PEDOT:PSS was sensitive to moisture and air, and the low work function metal cathode was easily oxidized to air, resulting in decreased efficiency in half per day [2]. Inverted organic solar cells (IOSCs) using high work function metal and buffer layer replacing the PEDOT:PSS have focused as a solution in conventional organic solar cell. On the contrary to conventional OSCs, ZnO and TiO2 are required to be used as a buffer layer, since the ITO in IOSC is used as cathode to collect electrons and block holes. The ZnO is expected to be excellent electron transport layer (ETL), because the ZnO has the advantages of high electron mobility, stability in air, easy fabrication at room temperature, and UV absorption. In this study, the IOSCs based on poly [N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) : [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) were fabricated with the ZnO electron-transport layer and MoO3 hole-transport layer. Thickness of the ZnO for electron-transport layer was controlled by rotation speed in spin-coating. The PCDTBT and PC70BM were mixed with a ratio of 1:2 as an active layer. As a result, the highest efficiency of 2.53% was achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.341-341
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• 2011

최근 AMOLED 구동이 가능한 소자에 대한 연구가 활발히 진행중이다. AMOLED구동 가능소자는 LTPS TFT, a-Si TFT, OTFT, Oxide TFT가 있으며 그 중에서 현재 대부분 LTPS TFT를 사용하고 있다. LTPS TFT는 높은 전자 이동도와 안정성을 가지고 있기 때문에 현재 각광 받는 AMOLED에 잘 맞는다. 하지만 LTPS TFT는 고비용, 250$^{\circ}C$ 이상의 공정온도, Substrate가 Glass, Metal로 제한 된다는 문제점이 있으며, 균일성이 낮고 현재 대면적 기술이 부족한 상태이다. 해결방안으로 AMOLED를 타겟으로 하는 Oxide TFT 기술이 떠오르고 있다. Oxide TFT는 이동도가 높고 저온공정이 가능하며 Substrate로 Plastic 기판을 사용할 수가 있어 차후에 Flexible 소자로서의 적용이 가능하다. 또한 기존의 진공장비 사용대신 용액공정이 가능하여 장비사용시간 및 절차를 단축시킬 수 있어 비용적인 유리함을 가지고 있다. Oxide TFT는 단결정 산화물과 다결정 복합 산화물 두 가지 범주를 가지고 있다. Oxide TFT의 재료물질은 ZnO, ZTO, IZO, SnO2, Ga2O3, IGO, In2O3, ITO, InGaO3(ZnO)5, a-IGZO이 있다. 본 연구에서는 산화물질 중 하나인 ZTO를 이용하여 TFT 소자를 제작하였다. 산화물 특성상 열처리 온도에 따라 형성되는 결정의 정도가 다르기 때문에 온도 및 시간 변수에 따른 ZTO의 특성변화에 초점을 맞추어 연구함으로서 최적화된 조건을 찾고자 실험을 진행하였다. 실험을 위한 기판으로 n-type wafer을 사용하였다. PE-CVD 장비를 이용하여 SiNx를 120 nm 증착하고, ZTO 용액을 spin-coating을 이용하여 channel layer을 형성하였다. 균일하게 형성된 ZTO의 결정을 위하여 200$^{\circ}C$, 300$^{\circ}C$, 400$^{\circ}C$, 500$^{\circ}C$에서 1시간, 3시간, 6시간, 10시간의 온도 및 시간 변수를 두어 공기 중에서 열처리 하였다. ZTO는 약 30 nm 두께로 형성되었다. Thermal evaporator를 이용하여 Source, Drain의 알루미늄 전극을 형성하고, wafer 뒷면에는 Silver paste를 이용하여 Gate전극을 만들었다. 제작된 소자를 dark room temperature에서 측정하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.396-396
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• 2013

The resistive random access memory (ReRAM) has several advantages to apply next generation non-volatile memory device, because of fast switching time, long retentions, and large memory windows. The high mobility of monolayered graphene showed several possibilities for scale down and electrical property enhancement of memory device. In this study, the monolayered graphene grown by chemical vapor deposition was transferred to $SiO_2$ (100 nm)/Si substrate and glass by using PMMA coating method. For formation of metal-oxide nanoparticles, we used a chemical reaction between metal films and polyamic acid layer. The 50-nm thick BPDA-PDA polyamic acid layer was coated on the graphene layer. Through soft baking at $125^{\circ}C$ or 30 min, solvent in polyimide layer was removed. Then, 5-nm-thick indium layer was deposited by using thermal evaporator at room temperature. And then, the second polyimide layer was coated on the indium thin film. After remove solvent and open bottom graphene layer, the samples were annealed at $400^{\circ}C$ or 1 hr by using furnace in $N_2$ ambient. The average diameter and density of nanoparticle were depending on annealing temperature and times. During annealing process, the metal and oxygen ions combined to create $In_2O_3$ nanoparticle in the polyimide layer. The electrical properties of $In_2O_3$ nanoparticle ReRAM such as current-voltage curve, operation speed and retention discussed for applictions of transparent and flexible hybrid ReRAM device.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1091-1097
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• 2015

Graphite material has been widely used for making the rocket nozzle throat because of its excellent thermal properties. However, when compared with typical structural materials, graphite is relatively weak with respect to both strength and toughness, owing to its quasi-brittle behavior, and gets oxidized at $450^{\circ}C$. Therefore, it is important to evaluate the thermal and mechanical properties of this material for using it in structural applications. This study presents an experimental method to investigate the fracture behavior of ATJ graphite at elevated temperatures. In particular, the effects of major parameters such as temperature, loading, and oxidation conditions on strength and fracture characteristics were investigated. Uniaxial compression and tension tests were conducted in accordance with the ASTM standard at room temperature, $500^{\circ}C$, and $1,000^{\circ}C$. Fractography analysis of the fractured specimens was carried out using an SEM.

• Korean Journal of Materials Research
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• v.26 no.2
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• pp.84-89
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• 2016

We present the rectifying and nitrogen monoxide (NO) gas sensing properties of an oxide semiconductor heterostructure composed of n-type zinc oxide (ZnO) and p-type copper oxide thin layers. A CuO thin layer was first formed on an indium-tin-oxide-coated glass substrate by sol-gel spin coating method using copper acetate monohydrate and diethanolamine as precursors; then, to form a p-n oxide heterostructure, a ZnO thin layer was spin-coated on the CuO layer using copper zinc dihydrate and diethanolamine. The crystalline structures and microstructures of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy. The observed current-voltage characteristics of the p-n oxide heterostructure showed a non-linear diode-like rectifying behavior at various temperatures ranging from room temperature to $200^{\circ}C$. When the spin-coated ZnO/CuO heterojunction was exposed to the acceptor gas NO in dry air, a significant increase in the forward diode current of the p-n junction was observed. It was found that the NO gas response of the ZnO/CuO heterostructure exhibited a maximum value at an operating temperature as low as $100^{\circ}C$ and increased gradually with increasing of the NO gas concentration up to 30 ppm. The experimental results indicate that the spin-coated ZnO/CuO heterojunction structure has significant potential applications for gas sensors and other oxide electronics.

• Journal of Powder Materials
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• v.28 no.3
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• pp.201-207
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• 2021

Ni-Cr-Al metal-foam-supported catalysts for steam methane reforming (SMR) are manufactured by applying a catalytic Ni/Al₂O₃ sol-gel coating to powder alloyed metallic foam. The structure, microstructure, mechanical stability, and hydrogen yield efficiency of the obtained catalysts are evaluated. The structural and microstructural characteristics show that the catalyst is well coated on the open-pore Ni-Cr-Al foam without cracks or spallation. The measured compressive yield strengths are 2-3 MPa at room temperature and 1.5-2.2 MPa at 750℃ regardless of sample size. The specimens exhibit a weight loss of up to 9-10% at elevated temperature owing to the spallation of the Ni/Al₂O₃ catalyst. However, the metal-foam-supported catalyst appears to have higher mechanical stability than ceramic pellet catalysts. In SMR simulations tests, a methane conversion ratio of up to 96% is obtained with a high hydrogen yield efficiency of 82%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.974-978
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• 2012

The effect of Cu coating on the sensing properties of nano $SnO_2:Cu$ based sensors for the $CH_4$, $CH_3CH_2CH_3$ gas was studied. This work was focussed on investigating the change of sensitivity of nano $SnO_2:Cu$ based sensors for $CH_4$, $CH_3CH_2CH_3$ gas by Cu coating. Nano sized $SnO_2$ powders were prepared by solution reduction method using stannous chloride($SnCl_2{\cdot}2H_2O$), hydrazine($N_2H_2$) and NaOH and subsequent heat treatment. XRD patterns showed that nano $SnO_2$ powders with rutile structure were grown with (110), (101), (211) dominant peak. The particle size of nano $SnO_2:Cu$ powders at 8 wt% Cu was about 50 nm. $SnO_2$ particles were found to contain many pores, according to SEM analysis. The sensitivity of nano $SnO_2:Cu$ based sensors was measured for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air with that in target gases. The sensitivity for both $CH_4$ and $CH_3CH_2CH_3$ gases was improved by Cu coating on the nano $SnO_2$ surface. The response time and recovery time of the $SnO_2:Cu$ gas sensors for the $CH_4$ and $CH_3CH_2CH_3$ gases were 18~20 seconds, and 13~15 seconds, respectively.

• The Journal of Engineering Research
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• v.3 no.1
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• pp.181-187
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• 1998

Hydroxyapatite was used as implant materials, because it has a good biocompatibility and is similar to human bone. However it is not expected to have a high strength as implant materials because of a low fracture strength after sintering of HAp. Alumina ($\alpha$-alumina) shows a stable chemical properties and high strength in physiological environments. Thus it was tried to use a HAp coatings on Alumina substrate as implant materials. In this study, HAp was coated on Alumina substrate by lon Beam Assisted Deposition(IBAD). Then Ag was impregnated on HAp coating layer, which showed antimicrobial effects. To carry out the ion exchange of $Ag^+$ with $Ca^{2+}$ in HAp on the surface, HAp coated alumina substrate was immersed in 20ppm, 100ppm $AgNO_3$ solution at room temperature for 48 hours. Antimicrobial test was studied by using bacteria, which normally caused periprosthetic infections. The follwing bacteria was used in antimicrobial test. Escherichia coli, Pseudomonas aeruginosa (gram negative) and staphylococcus epidermidis (gram positive). Ag impregnated HAp shows very good antimicrobial effects against these bacteria. The surface structure of sample, which was treated in $AgNO_3$ solution was studied by SEM, XRD. Ag release curve was studied in Simulated Body Fluid (SBF) solution.

• Conservation Science in Museum
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• v.7
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• pp.53-62
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• 2006

The wooden armor frame and various lacquerware artifacts excavated from the low swamp remains in Imdang, Gyeongsan have very weak material and lacquer coating; in case they are exposed in the air, they are likely to be shrunken and deformed immediately. The wooden armor frame has large size and it might be dissolved during freeze-drying. The lacquer coating of lacquerware blocks the penetration of chemicals and it is very likely to swell or peel off during the treatment. Therefore, to prevent the dissolution during vacuum freeze-drying, the wooden armor frame was replaced with t-butanol and impregnated in t-butanol solution with PEG#3, 350 43%, and lacquerware was impregnated in PEG#3, 350 40% solution at room temperature and freeze-dried. According to the analysis of the lacquer fragment from the lacquerware, the lid and the mounted cup was pasted with the mixture of lacquer and black pigment (soot) on the base layer after the first coating and pasted two or three times more with natural lacquer; the red lacquered wooden cup was pasted with the mixture of lacquer and black pigment on the base layer and pasted once on the middle layer. The top lacquer (red) was pasted with the mixture of iron oxide(Fe₂O₃).