• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1645-1647
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• 1996

Polycrystalline CdTe thin films -have been studied for photovoltaic application because of their high absorption coefficient and optimal band gap energy (1.54 eV) for solar energy conversion. In this study, we prepared CdTe films using RF-magnetron sputtering method and investigated structural, optical and electrical properties with spectrophotometer, XRD, EDX, and resistivity meter. CdTe films at $200\;^{\circ}C$ showed a mixture of zinc blend (Cubic) and wurtzite (hexagonal) phase. On the other hand, the films at $400\;^{\circ}C$ showed highly oriented structure having hexagonal structure. The resistivity of CdTe films deposited on $SiO_2$ substrates was about $10_7\;{\Omega}cm$. The value of resistivity decreased with the increase of the substrate temperature. CdTe were sputtered on CdS thin films prepared by chemical bath deposition for the formation of the heterojunction. I-V characteristics of these cells were measured at a light density of $100mw/cm^2$, AM. 1.0. The present thin film solar cells showed a conversion efficiency of about 5%.

• Electrical & Electronic Materials
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• v.10 no.9
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• pp.930-937
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• 1997

Polycrystalline CdTe thin films have been studied for photovoltaic application because of their high absorption coefficient and optimal band energy(1.45 eV) for solar energy conversion. In this study CdTe thin films were deposited on CdS(chemical bath deposition)/ITO(indium tin oxide) substrate by rf-magnetron sputtering under various conditions. Structural optical and electrical properties are investigated with XRD UV-Visible spectrophotometer SEM and solar simulator respectively. The fabricated CdTe/CdS solar cell exhibited open circuit voltage( $V_{oc}$ ) of 610 mV short circuit current density( $J_{sc}$ ) of 17.2 mA/c $m^2$and conversion efficiency of about 5% at optimal sputtering conditions.

• Journal of the Korean institute of surface engineering
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• v.50 no.2
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• pp.114-118
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• 2017

Bismuth telluride ($Bi_2Te_3$) and its alloys are well-known thermoelectric materials for ambient temperature applications. In this study, the dissolved Bi-Te precursor solution was used to synthesis metallic $Bi_2Te_3$ powder via ultrasonic spray pyrolysis and reduction process. The droplets of the Bi-Te precursor solution were decomposed to Bi-Te oxide powders by ultrasonic spray pyrolysis. The spherical $Bi_2Te_3$ powders were synthesized by reduction reaction in atmosphere of hydrogen gas at the temperature above $375^{\circ}C$ for 6h. The reduced $Bi_2Te_3$ powders have a mean particle size of $1.5{\mu}m$. The crystal structure of the powder was evaluated by X-Ray diffraction(XRD), and the microstructure with size and shape powders was observed by fieldemission scanning electron microscope(FE-SEM) and transmission electron microscope(TEM).

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.81-85
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• 2007

MnTe layers of high crystalline quality were successfully grown on Si(100) : B and Si(111) substrates by molecular beam epitaxy (MBE). Under tellurium-rich condition and the substrate temperature around $400^{\circ}C$, a layer thickness of $700{\AA}$ could be easily obtained with the growth rate of $1.1 {\AA}/s$. We investigated the structural, magnetic and transport properties of MnTe layers by using x-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry, and physical properties measurement system (PPMS). Characterization of MnTe layers on Si(100) : B and Si(111) substrates by XRD revealed a hexagonal structure of polycrystals with lattice parameters, ${\alpha}=4.143{\pm}0.001{\AA}\;and\;c=6.707{\pm}0.001{\AA}$. Investigation of magnetic and transport properties of MnTe films showed anomalies unlike antiferromagnetic powder MnTe. The temperature dependence of the magnetization data taken in zero-field-tooling (ZFC) and field-cooling (FC) conditions indicates three magnetic transitions at around 21, 49, and 210 K as well as the great irreversibility between ZFC and FC magnetization in the films. These anomalies are attributable to a magnetic-elastic coupling in the films. Magnetization measurements indicate ferromagnetic behaviour with hysteresis loops at 5 and 300 K for MnTe polycrystalline film. The coercivity ($H_c$) values at 5 and 300 K are 55 and 44 Oe, respectively. In electro-transport measurements, the temperature dependence of resistivity revealed a noticeable semiconducting behaviours and showed conduction via Mott variable range hopping at low temperatures.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.178-178
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• 2003

• Journal of the Korean Chemical Society
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• v.53 no.5
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• pp.530-535
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• 2009

Dicyclohexyl telluride was obtained in a high yield by the reaction of cyclohexyl bromide with NaTeH(prepared in situ) in an aqueous ethanolic solution. A series of new organotelluronium salts of the general formula ${(cyclo-C_6H_11)}_2Te(R)X$ (where R = $CH_3$, X = I (1); R = $C_2H_5$, X = Br(2); R = $C_2H_5$, X = I (3); R = C_3H_5$, X = Br (4)) were prepared by the reaction of ${(cyclo-C_6H_11)}_2Te$ with the corresponding alkyl halide. Reaction of 1 with NaBPh4 gave compound 5 ( i.e. R = CH3, X = BPh4 ‒) in 78% yield. Reaction of ${(cyclo-C_6H_11)}_2Te$ with benzyl bromide and 4-bromophenacyl bromide gave unexpectedly dibenzylcyclohexyltelluronium bromide (6) and bis(4-bromophenacyl)cyclohexyltelluronium bromide (7), respectively. Reaction of 6 with NaBPh4 gave the corresponding tetraphenylborate derivative (8) in high yield. $^1H$ NMR studies revealed that in $CDCl_3$solution compound 1 eliminated alkyl halide. Conductivity, IR, $^1H\;and\;^{13}C$ NMR and thermal data for the new compounds are presented and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.334-345
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• 2008

컴퓨터의 발달과 더불어 현대사회는 기록하고 보존해야할 정보의 양이 점점 방대해 지고 있다. 그로 인해 자기기록매체처럼 정보를 사용자의 편의에 따라 반복적으로 기록하고 재생할 수 있는 광기록매체에 대한 관심이 증가되고 있다. $Ge_2Sb_2Te_5$(GST)는 기존의 CD-RW나 Floppy Disk(FD)를 대체할 차세대 기록매체로 주목받고 있다. 따라서 본 연구에서는 비정질상과 결정상으로 변하는 성질을 가지고 있는 GST롤 상변화 기록매체로서 이용하기 위해 굴절률을 평가하였다. 시료는 5N의 순도를 갖는 Ge, Sb, Te 물질을 준비하고 조성비에 맞추어서 석영관에 진공 봉입한 후 용융-냉각법으로 벌크를 제작하였고 열증착 방법으로 Si 및 유리 기판위에 1000nm 두께로 박막을 제작하였다. UV-Vis-IR spectrophotometer를 사용하여 반사도와 투과도를 측정하였고 측정한 스펙트럼을 이용하여 Swanepoel method로 굴절률을 계산하였다. 본 연구진이 자체 개발한 계산툴에 실험값을 대입하였고 실험에 의해 얻은 투과도와 계산툴에 의해 얻은 투과도 스펙트럼을 비교하였다.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.178-181
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• 2006

We have investigated the Mn concentration-dependent structural, optical, magnetic properties in IV-VI diluted magnetic semiconductor $Si_{1-x}Mn_xTe_{1.5} $ crystals prepared by the vertical Bridgman technique. X-ray studies showed the single crystalline hexagonal crystal structure. From the optical absorption measurements energy band gap were found to decreases with increasing x and temperature. From the magnetization measurements the samples had ferromagnetic ordering with Curie temperature $T_C$ about 80 K. With increasing Mn concentration, the average magnetic moments per Mn atom determined from the saturated magnetization increased.

• Journal of the Korean Vacuum Society
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• v.5 no.4
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• pp.348-353
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• 1996

Rapid thermal annealing (RTA) was applied to polycrystalline CdTe thin films evaporated on CdS/ITO/glass substrate and the effect of the annealing temperatures and the atmosphere on physical properties of polycrystalline CdTe thin films and CdTe/CdS solar cell characteristics were studied. Results obtained by EDX showed that the bulk composition of CdTe remained stoichiometric after annealing at $550^{\circ}C$ in the air but the surface composition became Cd-rich. Cross-sectional TEM and micro EDX showed that columnar grains and micro-twins remained even after RTA, however, and the sulfur content in the annealed CdTe (added by sulfur diffusion from CdS during the annealing) was much smaller than that by furnace annealing. Among the investigated RTA temperatures and gas environments, the cell made with CdTe annealed at $550^{\circ}C$ in air showed the best solar energy conversion efficiency.

• Korean journal of food and cookery science
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• v.26 no.3
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• pp.246-251
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• 2010

This study was conducted to investigate the quality characteristics of guavapyun after the addition of different ratios of extract (0.25, 0.5, 0.75, 1.0%), non-extract and vitamin C. The quality if the pyun containing 0.5% of the guava fruit extract (guavapyun) and vitamin C was higher compared with the quality of the control pyun. In the results of the proximatecomposition, the content of water was high in the control pyun relative to the vitamin C pyun and guavapyun and the carbohydrate, ash, crude lipid and protein content was high in guavapyun. The sweetness, pH and color (L, a, b value) were very high in the samples. The texture, hardness, chewiness and gumminess were significantly high in the control pyun and the adhesiveness and cohesiveness were high in guavapyun. However, there were no significant differences in springiness between the control and the added samples. The total phenolic content was higher in guavapyun (23.57 mg GAE/100 g) than the control pyun (18 mg GAE/100 g) and vitamin C pyun(15.05 mg GAE/100 g). The antioxidant activities determined by the DPPH method and ABTS method was higher in guavapyun (41.37 mM TE/g, 15.35 mM TE/g) than the control pyun (4.43 mM TE/g, 2.17mM TE/g) and vitamin C pyun (11.33 mM TE/g, 4.51 mM TE/g). Using the FRAP method, guavapyun(9.06 mM TE/g) was shown to exhibit a stronger ferrous ion chelating activity than the control pyun (4.49mM TE/g) and vitamin C pyun (7.03 mM TE/g). Thus, the studied indigenous guavapyun was high in both antioxidative activity and total phenolic content.