• Title, Summary, Keyword: Microwave microscopy

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Growth of Carbon Nanotubes by Microwave Plasma Enhanced Chemical Vapor Deposition (마이크로웨이브 플라즈마 화학기상증착법에 의한 탄소나노튜브의 성장특성)

  • Choi Sung-Hun;Lee Jae-Hyeoung
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.19 no.6
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    • pp.501-506
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    • 2006
  • Carbon nanotubes (CNTs) were grown with a microwave plasma enhanced chemical vapor deposition (MPECVD) method, which has been regarded as one of the most promising candidates for the synthesis of CNTs due to the vertical alignment, the low temperature and the large area growth. MPECVD used methane ($CH_4$) and hydrogen ($H_2$) gas for the growth of CNTs. 10 nm thick Ni catalytic layer were deposited on the Ti coated Si substrate by RF magnetron sputtering method. In this work, the pretreatment was that the Ni catalytic layer in different microwave power (600, 700, and 800 W). After that, CNTs deposited on different pressures (8, 12, 16, and 24 Torr) and grown same microwave power (800 W). SEM (Scanning electron microscopy) images showed Ni catalytic layer diameter and density variations were dependent with their pretreatment conditions. Raman spectroscopy of CNTs shows that $I_D/I_G$ ratios and G-peak positions vary with pretreatment conditions.

Electrochemical Properties of Li[Ni0.2Li0.2Mn0.6]O2 by Microwave-assisted Sol-gel Method

  • Park, Yong-Joon;Kim, Seuk-Buom
    • Transactions on Electrical and Electronic Materials
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    • v.10 no.3
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    • pp.102-105
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    • 2009
  • $Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ cathode materials have been synthesized by a microwave-assisted sol-gel method. The structure and electrochemical properties of $Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ were studied by X-ray difftactometry (XRD), scanning electron microscopy (SEM) and charge-discharge cycler. The powder prepared by microwave assisted sol-gel method showed good crystallinity and well-defined facet shapes. The $Li[Ni_{0.2}Li_{0.2}Mn_{0.6}]O_2$ electrode delivered a high discharge capacity of 230 $mAhg^{-1}$ at the specific current of 40 $mAg^{-1}$ (0.2 C rate) in the voltage range of 2.0${\sim}$4.8 V. About 60 % of the discharge capacity measured at 0.2 Crate (140 $mAhg^{-1}$) was maintained at a 6 C (1200 $mAg^{-1}$)rate. The cyclic property was also stable and it did not deteriorated at a high Crate.

Microwave Dielectric Characteristics of $Ba(Mg_{1/3}Nb_{2/3})O_3$ - $La(Mg_{2/3}Nb_{1/3})O_3$ Solid Solutions with Crystal Structure (결정구조에 의한 $Ba(Mg_{1/3}Nb_{2/3})O_3$ - $La(Mg_{2/3}Nb_{1/3})O_3$고용체의 마이크로파 유전 특성)

  • Paik, Jong-Hoo;Lim, Eun-Kyeong;Lee, Mi-Jae;Choi, Byung-Hyun;Nahm, Sahn
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.738-743
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    • 2004
  • The microwave dielectric properties and their related structural characteristics in solid solutions of (1-x) $Ba(Mg_{1/3}Nb_{2/3})O_3$ -x $La(Mg_{2/3}Nb_{1/3})O_3$ (BLMN) have been investigated by measuring the dielectric constant${\varepsilon}r)$, Q value and temperature coefficient of resonant frequency$({\tau}f)$ and by observing the crystal structure using high resolution transmission electron microscopy (HRTEM). Microwave dielectric properties showed characteristic features for specific composition. Dielectric constant$({\varepsilon}r)$ showed maximum value at the composition which corresponds to the phase boundary between 1:2 ordered and 1:1 ordered structure. The increase in ${\varepsilon}_r$ may be caused by the rattling of ions by incorporating smaller ions and the disordered structure. The variation of temperature coefficient of resonant frequency${{\tau}_f)$ was investigated in terms of oxygen octahedra tilting.

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Synthesis of Praseodymium-Doped TiO2 Nanocatalysts by Sol-Microwave and Their Photocatalytic Activity Study

  • Huang, Fengping;Wang, Shuai;Zhang, Shuang;Fan, Yingge;Li, Chunxue;Wang, Chuang;Liu, Chun
    • Bulletin of the Korean Chemical Society
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    • v.35 no.8
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    • pp.2512-2518
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    • 2014
  • The praseodymium-doped $TiO_2$ photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of $TiO_2$. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was $500^{\circ}C$ for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by $Pr^{3+}$.

Nonstoichiometric Addition of ZrO2 and NiO to the Ba(Zn1/3Ta2/3)O3 Microwave Dielectrics (Ba(Zn1/3Ta2/3)O3 마이크로파 유전체에서 ZrO2와 NiO의 비화학양론적 첨가)

  • Nam, Kyung-Deog;Kang, Sung-Woo;Kim, Tae-Heui;Sim, Soo-Man;Choi, Sun-Hee;Kim, Joo-Sun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.12
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    • pp.955-961
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    • 2011
  • We investigated the physical properties of stoichiometric and non-stoichiometric oxide doped complex perovskite, $Ba(Zn_{1/3}Ta_{2/3})O_3$ ceramics and their impacts on the microwave dielectric performances using various characterization techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and network analyzer. According to the measurement of lattice constant changes, anomalous lattice volume contraction of $ZrO_2$ doped $Ba(Zn_{1/3}Ta_{2/3})O_3$ sample only showed the dielectric quality factor enhancements, which was due to the lattice volume contraction as well as the 1:2 B-site cation ordering. In addition, NiO doping was useful to the stabilization of temperature coefficient of resonance frequency.

Growth of carbon nanotubes on metal substrates using microwave plasma-enhanced chemical vapor deposition (금속 기판 위에 성장한 탄소나노튜브 특성에 관한 연구)

  • 김현숙;박성렬;양지훈;문상현;박종윤;박래준
    • Journal of the Korean Vacuum Society
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    • v.11 no.4
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    • pp.256-260
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    • 2002
  • Carbon nanotubes on metal(SUS304) substrates were synthesized by using micro-wave plasma-enhanced chemical vapor deposition at $650^{\circ}C$ with gas mixture CH$_4$(11%) and H$_2$(89%). Their structure was investigated by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy was also used to justify the structure and crystallinity of graphite sheets. High-resolution transmission electron microscopy images clearly showed carbon nanotubes to be multwalled. The measured turn-on field and current density obtained from I-V measurement were 4.4 V/$\mu \textrm{m}$ and $8.4\times10^1\mu\textrm{A}/\textrm{cm}^2$, respectively.

Effect of CuO-V2O5 Addition on Microwave Dielectric Properties of (Pb0.45Ca0.55(Fe0.5Nb0.5)0.9Sn0.1]O3 Ceramics

  • Ha, Jong-Yoon;Choi, Ji-Won;Yoon, Ki-Hyun;Choi, Doo-Jin;Yoon, Seok-Jin;Kim, Hyun-Jai
    • Journal of the Korean Ceramic Society
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    • v.41 no.1
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    • pp.9-12
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    • 2004
  • The effect of x wt% CuO-y wt% $V_2O_5$ content on the microwave properties of $(Pb_{0.45}Ca_{0.55})[(Fe_{0.5}Nb_{0.5})_{0.9}Sn_{0.1}]O_3$ (PCFNS) ceramics was investigated. In order to decrease the sintering temperature and use as a Low Temperature co-firing Ceramics (LTCC), CuO-$V_2O_5$ are added in the PCFNS. The bulk density, dielectric constant (${\varepsilon}_r$) and quality factor(Q${\cdot}f_0$) increased with increase in CuO content within a limited value. The microwave properties were degraded with increases in $V_2O_5$ content. The temperature coefficient of the resonant frequency (${\tau}_f$) of PCFNS was shifted to positive value abruptly with increasing the $V_2O_5$ content, while the ${\tau}_f$ was slightly shifted to positive value with increasing the CuO content. The optimized microwave properties, ${\varepsilon}_r$ = 88, Q${\cdot}f_0$ = 6100 (GHz), and ${\tau}_f$ = 18 ppm/$^{\circ}C$, were obtained in $(Pb_{0.45}Ca_{0.55})[(Fe_{0.5}Nb_{0.5})_{0.9}Sn_{0.1}]O_3$ with 0.2wt% CuO 0.05 wt% $V_2O_5$ and sintered at $1000^{\circ}C$ for 3 h. The relationship between the microstructure and microwave dielectric properties of ceramics was studied by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM)

Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition

  • Kim, Y.;Song, W.;Lee, S.Y.;Jung, W.;Kim, M.K.;Jeon, C.;Park, C.Y.
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.80-80
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    • 2010
  • Graphene has attracted tremendous attention for the last a few years due to it fascinating electrical, mechanical, and chemical properties. Up to now, several methods have been developed exclusively to prepare graphene, which include micromechanical cleavage, polycrystalline Ni employing chemical vapor deposition technique, solvent thermal reaction, thermal desorption of Si from SiC substrates, chemical routes via graphite intercalation compounds or graphite oxide. In particular, polycrystalline Ni foil and conventional chemical vapor deposition system have been widely used for synthesis of large-area graphene. [1-3] In this study, synthesis of mono-layer graphene on a Ni foil, the mixing ratio of hydrocarbon ($CH_4$) gas to hydrogen gas, microwave power, and growth time were systemically optimized. It is possible to synthesize a graphene at relatively lower temperature ($500^{\circ}C$) than those (${\sim}1000^{\circ}C$) of previous results. Also, we could control the number of graphene according to the growth conditions. The structural features such as surface morphology, crystallinity and number of layer were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), transmission electron microscopy (TEM) and resonant Raman spectroscopy with 514 nm excitation wavelength. We believe that our approach for the synthesis of mono-layer graphene may be potentially useful for the development of many electronic devices.

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The effects of mineral salt catalysts on selectivity of phenolic compounds in bio-oil during microwave pyrolysis of peanut shell

  • Mamaeva, Alisa;Tahmasebi, Arash;Yu, Jianglong
    • The Korean Journal of Chemical Engineering
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    • v.34 no.3
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    • pp.672-680
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    • 2017
  • Catalytic microwave pyrolysis of peanut shell (PT) using $Fe_3O_4$, $Na_2CO_3$, NaOH, and KOH for production of phenolic-rich bio-oil was investigated. The effects of catalyst type, pyrolysis temperature, and biomass/catalyst ratio on product distribution and composition were studied. Among four catalysts tested, $Na_2CO_3$ significantly increased the selectivity of phenolic compounds in bio-oil during microwave pyrolysis. The highest phenolics concentration of 57.36% (area) was obtained at $500^{\circ}C$ and $PT:Na_2CO_3$ ratio of 8 : 1. The catalytic effect to produce phenolic compounds among all the catalysts tested can be summarized in the order $Na_2CO_3$>$Fe_3O_4$>KOH>NaOH. Using KOH and NaOH as catalyst resulted in formation of bio-oil with enhanced higher heating value (HHV) and lower oxygen content, indicating that these catalysts enhanced the deoxygenation of bio-oil. The scanning-electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis of char particles showed the melting of magnetite and vaporization-condensation of mineral salt catalysts on char particle, which was attributed to extremely high local temperatures during microwave heating.

Preparation of Submicron Nickel Powders with Non-aqueous Solvent In Microwave-Assisted Reduction Method (비수계 용매를 사용하는 마이크로파 환원법에 의한 서브마이크론 니켈 분말의 합성)

  • Jeon, Seung Yup;Kim, Jae-Hwan;Park, Na Yi;Park, Hoy Yul;Lee, Gun-Dae;Hong, Seong-Soo;Park, Seong Soo
    • Applied Chemistry for Engineering
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    • v.18 no.4
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    • pp.320-325
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    • 2007
  • Nickel powders were prepared from an aqueous nickel acetate solution and hydrazine hydrate using diethanolamine as the nonaqueous organic solvent in the conventional and microwave synthetic method. It was investigated that microwave non-thermal effect and synthetic condition affect the preparation of nickel powders by means of X-ray diffractometry, scanning electron microscopy, thermal gravymetry analysis, and X-ray photoelectron spectroscopy analysis. Compared with the conventional synthetic method, less of aggregation, smaller particle size, and more uniform distribution of particle size were obtained in the microwave synthetic method due to the non-thermal effect of microwaves.