• Title/Summary/Keyword: S-doping

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c-axis Tunneling in Intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ Single Crystals

  • Lee, Min-Hyea;Chang, Hyun-Sik;Doh, Yong-Joo;Lee, Hu-Jong;Lee, Woo;Choy, Jin-Ho
    • 한국초전도학회:학술대회논문집
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    • v.9
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    • pp.260-260
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    • 1999
  • We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

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A Study on the Organic/inorganic Composite Electrolyte Membranes for Dye Sensitized Solar Cell (염료감응형 태양전지를 위한 유기/무기 복합 전해질막에 대한 연구)

  • Koo, Ja-Kyung;Choi, Mi-Jung;Shin, Chun-Hwa;Kang, Tae-Un;Cho, Nam-Jun
    • Membrane Journal
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    • v.18 no.4
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    • pp.345-353
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    • 2008
  • Organic/inorganic composite electrolyte membranes were prepared for dye sensitized solar cell (DSSC). Polyethylene Glycol (PEG)s with various molecular weight (400, 600, 1,500 and 3,400) was ethoxysilated to fabricate organic/inorganic composite materials through sol-gel processes. The electrolyte membranes were produced by doping the composite materials with NaI and $I_2$, and their ionic conducting behavior was investigated. The ionic conductivity of the composite electrolyte was highly affected by the PEG molecular weight, and the highest conductivity was shown by the composite membrane prepared with PEG with the molecular weight of 1,500. The composite electrolyte membranes showed considerable improvement of ionic conductivity. Compared to PEO electrolyte membranes, the composite electrolyte membrane prepared by PEG, MW 1,500, showed much higher ionic conductivity.

Low-Temperature Si and SiGe Epitaxial Growth by Ultrahigh Vacuum Electron Cyclotron Resonance Chemical Vapor Deposition (UHV-ECRCVD)

  • Hwang, Ki-Hyun;Joo, Sung-Jae;Park, Jin-Won;Euijoon Yoon;Hwang, Seok-Hee;Whang, Ki-Woong;Park, Young-June
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1996.06a
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    • pp.422-448
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    • 1996
  • Low-temperature epitaxial growth of Si and SiGe layers of Si is one of the important processes for the fabrication of the high-speed Si-based heterostructure devices such as heterojunction bipolar transistors. Low-temperature growth ensures the abrupt compositional and doping concentration profiles for future novel devices. Especially in SiGe epitaxy, low-temperature growth is a prerequisite for two-dimensional growth mode for the growth of thin, uniform layers. UHV-ECRCVD is a new growth technique for Si and SiGe epilayers and it is possible to grow epilayers at even lower temperatures than conventional CVD's. SiH and GeH and dopant gases are dissociated by an ECR plasma in an ultrahigh vacuum growth chamber. In situ hydrogen plasma cleaning of the Si native oxide before the epitaxial growth is successfully developed in UHV-ECRCVD. Structural quality of the epilayers are examined by reflection high energy electron diffraction, transmission electron microscopy, Nomarski microscope and atomic force microscope. Device-quality Si and SiGe epilayers are successfully grown at temperatures lower than 600℃ after proper optimization of process parameters such as temperature, total pressure, partial pressures of input gases, plasma power, and substrate dc bias. Dopant incorporation and activation for B in Si and SiGe are studied by secondary ion mass spectrometry and spreading resistance profilometry. Silicon p-n homojunction diodes are fabricated from in situ doped Si layers. I-V characteristics of the diodes shows that the ideality factor is 1.2, implying that the low-temperature silicon epilayers grown by UHV-ECRCVD is truly of device-quality.

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A Study on Sintering Behavior and Conductivity for NiO-doped BaZr0.85Y0.15O3-δ (NiO가 도핑된 BaZr0.85Y0.15O3-δ의 소결거동 및 전도도에 관한 연구)

  • Park, Young-Soo;Kim, Jin-Ho;Kim, Hae-Kyoung;Hwang, Kwang-Tak
    • Transactions of the Korean hydrogen and new energy society
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    • v.23 no.6
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    • pp.670-677
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    • 2012
  • Perovskite-type oxides such as doped barium zirconate ($BaZrO_3$) show high proton conductivity and chemical stability when they are exposed to hydrogen and water vapour containing atmospheres, thus it can be applicable to the hydrogen separation and the fuel cell electrolyte membranes. However the high temperature ($1700-1800^{\circ}C$) and long sintering times (24h) are generally required to prepare the fully densified $BaZrO_3$ pellets. These sintering conditions lead to the limitation of the grain size growth and the degradation of conductivity due to the acceleration of BaO evaporation at $1200^{\circ}C$. Here we demonstrate NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ with lower calcination and sintering temperature, less experimental procedure and lower process cost than the conventional mixing method. The stoichiometry of $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was optimized by the control of excess amount of Ba (5mol%) to minimized BaO evaporation. We found that the crystal size of NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was increased with increase of calcination temperature from XRD analysis. NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ powder was calcined at $1000^{\circ}C$ for 12h when its showed the highest conductivity of $3.3{\times}10^{-2}s/cm$.

Multicrystalline Silicon Texturing for Large Area CommercialSolar Cell of Low Cost and High Efficiency

  • Dhungel, S.K.;Karunagaran, B.;Kim, Kyung-Hae;Yoo, Jin-Su;SunWoo, H.;Manna, U.;Gangopadhyay, U.;Basu, P.K.;Mangalaraj, D;Yi, J.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.11a
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    • pp.280-284
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    • 2004
  • Multicrystalline silicon wafers were textured in an alkaline bath, basically using sodium hydroxide and in acidic bath, using mainly hydrofluoric acid (HF), nitric acid $(HNO_3)$ and de-ionized water (DIW). Some wafers were also acid polished for the comparative study. Comparison of average reflectance of the samples treated with the new recipe of acidic solution showed average diffuse reflectance less than even 5 percent in the optimized condition. Solar cells were thus fabricated with the samples following the main steps such as phosphorus doping for emitter layer formation, silicon nitride deposition for anti-reflection coating by plasma enhanced chemical vapor deposition (PECVD) and front surface passivation, screen printing metallization, co-firing in rapid thermal processing (RTP) Furnace and laser edge isolation and confirmed >14 % conversion efficiency from the best textured samples. This isotropic texturing approach can be instrumental to achieve high efficiency in mass production using relatively low cost silicon wafers as starting material.

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Humidity Effect on the Characteristics of the Proton Conductor Based on the BaR0.5+xTa0.5-xO3-δ (R=Rare Earth) System (BaR0.5+xTa0.5-xO3-δ (R=희토류 금속)계 Proton 전도체 특성에 미치는 수분의 영향)

  • Choi, Soon-Mok;Seo, Won-Sun;Jeong, Seong-Min;Kim, Shin;Lee, Hong-Lim
    • Journal of the Korean Ceramic Society
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    • v.45 no.5
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    • pp.290-296
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    • 2008
  • $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structures which have been reported as proton conductors over $600^{\circ}C$ were studied. The $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure is known to be more easily synthesized and has better stability than normal $ABO_3$ perovskite structure. And it is stable at about $800^{\circ}C$ in the $CO_2$ atmosphere, whereas the $BaCeO_3$ perovskite is easily decomposed into carbonate. In addition, this $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure could simply produce oxygen vacancies within their structure not by introducing additional doping oxides but by just controling the molar ratio of $B'^{+3}$ and $B"^{+5}$ metal ions in the B site. Hence it is easy to design the structure which shows highly sensitive electrical conductivity to humidity. In this study, the single phase boundary of $BaR_{0.5+x}Ta_{0.5-x}O_{3-{\delta}}$(R = rare earth) complex perovskite structures and it's phase stability were investigated with changes in composition, x. And the humidity dependance of electrical conductivity at different $P_{H2O}$ conditions was investigated.

Spectro-electrochemical Analyses of Immobilization of Glucose Oxidase (Glucose Oxidase 고정화에 대한 전기화학적/광학적 분석)

  • Kim, Hyun-Cheol;Cho, Young-Jai;Gu, Hal-Bon;SaGon, Geon
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.05b
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    • pp.316-319
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    • 2000
  • In the case of immobilizing of glucose oxidase into polypyrrole (PPy) using electrosynthesis, the glucose oxidase (GOx) forms a coordinate bond with the polymer's backbone. However, because of intrinsic insulation and net-chain of the enzyme, the charge transfer and mass transport are obstructed during the film growth. Therefore, the film growth is dull. We synthesized the enzyme electrode by electropolymerization added some organic solvent, A formative seeds of film growth is delayed by adding the solvent. The delay is induced by radical transfer between the solvent and pyrrole monomer. In the case of adding ethanol, the radical transfer shares the contribution of dopant between electrolyte anion and GOx polyanion. This may lead to increase amount of immobilized the enzyme in ppy. However, adding tetrahydrofuran (THF), the radical transfer is more brisk, resulting in short chained polymer. Therefore, the doping level is lowered and then amount of immobilized of enzyme is decreased. For the UV absorption spectra of synthetic solution before synthesis and after, in the case of ethanol added, the optical density was slightly decreased for the GOx peaks. It suggests amount of GOx in the solution was decreased and amount of GOx in the film was increased. We established qualitatively that amount of immobilization can be improved by adding a little ethanol in the synthetic solution. It is due to radical transfer reaction. The radical transfer shares the contribution of dopant between small and fast electrolyte anion and big and slow GOx polyanion.

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Simulation of Junction Field Effect Transistor using SiGe-Si-SiGe Channel Structure (SiGe-Si-SiGe 채널구조를 이용한 JFET 시뮬레이션)

  • Park, B.G.;Yang, H.Y.;Kim, T.S.;Shim, K.H.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.11a
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    • pp.94-94
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    • 2008
  • We have performed simulation for Junction Field Effect Transistor(JFET) using Silvco to improve its electrical properties. The device structure and process conditions of Si-control JFET(Si-JFET) were determined to set its cut off voltage and drain current(at Vg=0V) to -0.5V and $300{\mu}A$, respectively. From electrical property obtained at various implantation energy, dose, and drive-in conditions of p-gate doping, we found that the drive in time of p-type gate was the most determinant factor due to severe diffusion. Therefore we newly designed SiGe-JFET, in which SiGe layer is to epitaxial layers placed above and underneath of the Si-channel. The presence of SiGe layer lessen the p-type dopants (Boron) into the n-type Si channel the phenomenon would be able to enhance the structural consistency of p-n-p junction. The influence of SiGe layer will be discussed in conjunction with boron diffusion and corresponding I-V characteristics in comparison with Si-control JFET.

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Effect of Particle Size and Doping on the Electrochemical Characteristics of Ca-doped LiCoO2 Cathodes

  • Hasan, Fuead;Kim, Jinhong;Song, Heewon;Lee, Seon Hwa;Sung, Jong Hun;Kim, Jisu;Yoo, Hyun Deog
    • Journal of Electrochemical Science and Technology
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    • v.11 no.4
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    • pp.352-360
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    • 2020
  • Lithium cobalt oxide (LiCoO2, LCO) has been widely used as a cathode material for Li-ion batteries (LIBs) owing to its excellent electrochemical performance and highly reproducible synthesis even with mass production. To improve the energy density of the LIBs for their deployment in electro-mobility, the full capacity and voltage of the cathode materials need to exploited, especially by operating them at a higher voltage. Herein, we doped LCO with divalent calcium-ion (Ca2+) to stabilize its layered structure during the batteries' operation. The Ca-doped LCO was synthesized by two different routes, namely solid-state and co-precipitation methods, which led to different average particle sizes and levels of dopant's homogeneity. Of these two, the solid-state synthesis resulted in smaller particles with a better homogeneity of the dopant, which led to better electrochemical performance, specifically when operated at a high voltage of 4.5 V. Electrochemical simulations based on a single particle model provided theoretical corroboration for the positive effects of the reduced particle size on the higher rate capability.

Properties of ZnO Films on r-plane Sapphires Prepared by Ultrasonic Spray Pyrolysis (초음파(超音波) 분무(噴霧) 열분해법(熱分解法)으로 r-plane 사파이어 위에 증착(蒸着)된 ZnO 막(膜)의 특성(特性))

  • Ma, Tae-Young;Moon, Hyun-Yul;Lee, Soo-Chul
    • Journal of Sensor Science and Technology
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    • v.6 no.2
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    • pp.155-162
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    • 1997
  • Zinc oxide(ZnO) thin films were deposited on r-plane sapphires from a solution containing zinc acetate. The films were obtained in a hot wall reactor by the pyrolysis of an aerosol produced by an ultrasonic generator. The crystallinity, surface morphology and composition of the films have been studied using the x-ray diffraction method(XRD) scanning electron microscopy(SEM) and Auger electron spectroscopy (AES) respectively. The influences of the substrate temperature on the crystallinity of the films were studied. Strongly (110) oriented ZnO films were obtained at a substrate temperature of $350^{\circ}C$. The resistivity was increased to above $3{\times}10^{6}{\Omega}{\cdot}cm$ with copper doping and vapor oxidation.

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