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[Ni?Fe?/Ag/Ni?Fe?]? 적층막의 자기저항 및 미세구조 분석
李準鎔,金永煥,吳昌烈 弘益大學校 科學技術硏究所 1997 科學技術硏究論文集 Vol.8 No.-
The microstructure and magnetic properties of Ni??Fe??/Ag multilayer film have been examined to investigate the magneto-resistance characteristics pre/post annealing. The DC & RF magnetron sputter unit has been used to prepare the sample. Annealing of the film has been conducted under the vacuum condition with various temperature. The bridging of Ag has been observed in TEM analysis which shows that Ag atom diffuses through the grain boundary of Ni??Fe??. The maximum saturation magnetization density is obtained at the thickness of 800Å film. The effective permeability is in the range between 1900 and 2800. Magneto-resistance curve of Ni??Fe??/Ag multilayer has maximum value at H=0 which decreases gradually with H.
Chang-Yeoul Kim,Seong-Geun Choa,Seok Park,최덕균 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.6
Peroxotungstic acid precursor solution was sprayed on indium-doped tin oxide (ITO) glass substrates to synthesize amorphous and crystalline phase tungsten oxide thin films by changing heating temperature. We could synthesize the amorphous phase at below 400℃ and the monoclinic crystalline tungsten oxide at above 400℃. Electrochemical and in-situ optical transmittance analysis showed that amorphous phase tungsten oxide at 250℃ had a good electrochromic property with a large optical transmittance change between its bleached and colored states. The coloration mechanisms are due to polaron generation by inserting ions and electrons to change W+6 state to W+5 or W+4 state. Peroxotungstic acid precursor solution was sprayed on indium-doped tin oxide (ITO) glass substrates to synthesize amorphous and crystalline phase tungsten oxide thin films by changing heating temperature. We could synthesize the amorphous phase at below 400℃ and the monoclinic crystalline tungsten oxide at above 400℃. Electrochemical and in-situ optical transmittance analysis showed that amorphous phase tungsten oxide at 250℃ had a good electrochromic property with a large optical transmittance change between its bleached and colored states. The coloration mechanisms are due to polaron generation by inserting ions and electrons to change W+6 state to W+5 or W+4 state.
Kim, Chang-Yeoul,Park, Yu-Sik American Scientific Publishers 2015 Journal of nanoscience and nanotechnology Vol.15 No.7
<P>We synthesized TiO2 nanoparticles (TPs) as a reference via hydrothermal method and also TiO2 aerogels (TAs) via CO2 supercritical drying method. We investigated crystal phase transformation behavior of TPs and TAs with temperature. As-prepared TPs are anatase and rutile phase transformation from anatase starts at 600 °C and was complete at 700 °C. However, TAs are amorphous phase until 300 °C and the crystallization to anatase occurs at 400 °C, and remains anantase phase until 700 °C. At the results of nitrogen adsorption and desorption analyses, TPs with specific surface area of 209 m2/g at 100 °C showed the decrease of the specific surface area and pore volume with increasing temperature and 95% of decrease at 700 °C. TAs showed higher specific surface area, 498 m2/g at 100 °C, and the decreasing trend according to temperature is similar with those of TPs. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). After results of DSC photocurrent conversion efficiency measurements of the three type cells, we found that TATPs showed the improved cell efficiency by 1% point, compared with a reference TPs below 15 micrometer thickness. In conclusion, the introduction of nanoporous TAs can improve the photocurrent conversion efficiency due to their high specific surface area for high dye adsorption without degrading of electron transfer.</P>
Kim, Chang-Yeoul,Park, Yu-Sik,Hwang, Hae-Jin American Scientific Publishers 2012 Journal of nanoscience and nanotechnology Vol.12 No.4
<P>To evaluate the effects of specific surface area to the photocurrent conversion efficiency of dye-sensitized solar cell (DSC), we adopted TiO2 aerogel (TA)/nanoparticle (TP) composite as a photoelectrode. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). The performance of TATP composite electrode was compared with that of TP and TAs. TATPs showed the improved cell efficiency, more than 0.5%, compared with a reference TPs below 15 micrometer thickness. Although the introduction of TAs increases the specific surface area for the dye adsorption, DSC composed of only TAs does not show the best efficiency result due to the crack generation. In conclusion, to produce the best photocurrent conversion efficiency, the high specific surface area of TiO2 photoelectrode for high dye adsorption should be balanced with proper control of the good electron transfer path.</P>
Self-heating of Magnetite Nanoparticles for a Potential Hyperthermia Application
Chang-Yeoul Kim,Lixing Xu,Eun-Hee Lee 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.2
A comparative study of heat generation in superparamagnetic magnetite nanoparticles in aqueousand hexane solutions in the presence of external magnetic field is presented. The field strengthdependence of the specific absorption rate (SAR) complies with the power law of second order. The concave-convex change of SAR-H curves substantially illustrates the importance of particledispersion in the fluid.
급성 천식발작시 혈장 및 요중 Endothelin 농도 변동
장중현 ( Jung Hyun Chang ),신태림 ( Tae Rim Shin ),우가은 ( Ga Eun Woo ),김종선 ( Jong Seon Kim ),홍은순 ( Eun Soon Hong ),서기열 ( Gi Yeoul Seo ),차주현 ( Joo Hyun Cha ),김미선 ( Mi Seon Kim ),김영선 ( Yeung Seon Kim ),조영주 ( Y 대한결핵 및 호흡기학회 1997 Tuberculosis and Respiratory Diseases Vol.44 No.4
Doping Ratio Control of Fluorine-Doped Tin Oxide for a High-Quality Transparent Conducting Electrode
Kim, Chang-Yeoul,Go, Eun-Byul,Choi, Jae-Seok,Choi, Sung Churl American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.11
<P>Transparent conducting oxides (TCOs) are very important materials for application in flat panel displays, thin-film solar cells, and touch panels. These days, the low-temperature synthesis of TCO thin films is being actively researched for realizing flexible electronics such as displays and solar cells. TCO thin films, mainly tin-doped indium oxide, are normally fabricated by high-vacuum sputtering. However, fluorine-doped tin oxide (FTO) has been in use for thin-film solar cells from the beginning. Our study attempts to lower the deposition temperature of FTO to 250 degrees C, which is suitable for deposition on polyimide substrates. We varied the F/Sn precursor ratio at different deposition temperatures, and found that a low F/Sn ratio of about 0.15 produces the lowest electrical resistivity below 350 degrees C, whereas a F/Sn ratio of 1.5 is obtained at 450 degrees C. At lower temperatures, crystal growth is very slow, and therefore, we should conduct very slow deposition to obtain high-quality TCO thin films.</P>
Effect of SiC and WC additon on Oxidation Behavior of Spark-Plasma-Sintered ZrB<sub>2</sub>
Kim, Chang-Yeoul,Choi, Jae-Seok,Choi, Sung-Churl The Korean Powder Metallurgy Institute 2019 한국분말재료학회지 (KPMI) Vol.26 No.6
ZrB<sub>2</sub> ceramic and ZrB<sub>2</sub> ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO<sub>2</sub> amorphous outer scale layer and SiC-deplete ZrO<sub>2</sub> scale layer, which decrease the oxidation rate. WC addition forms WO<sub>3</sub> during the oxidation process to result in a ZrO<sub>2</sub>/WO<sub>3</sub> liquid sintering layer, which is known to improve the anti-oxidation effect. The addition of SiC and WC to ZrB<sub>2</sub> reduces the oxygen effective diffusivity by one-fifth of that of ZrB<sub>2</sub>. The addition of both SiC and WC shows the formation of a SiO<sub>2</sub> outer dense glass layer and ZrO<sub>2</sub>/WO<sub>3</sub> layer so that the anti-oxidation effect is improved three times as much as that of ZrB<sub>2</sub>. Therefore, SiC- and WC-added ZrB<sub>2</sub> has a lower two-order oxygen effective diffusivity than ZrB<sub>2</sub>; it improves the anti-oxidation performance 3 times as much as that of ZrB<sub>2</sub>.
Kim, Chang Yeoul,Choi, Jin Wook,Lim, Tae Yeoung,Choi, Duck Kyun Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.317 No.-
<P>Electrochromic WO3 thin film was prepared by using tungsten metal solution in hydrogen peroxide as a starting solution and by sol-gel dip coating method. XRD pattern showed that tungsten oxide crystal phase formed at 400. In the view of electrochemical property, WO3 thin film which was heat-treated at 300 and was amorphous had better than that of the crystalline phase.</P>