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  • Title/Summary/Keyword: nano-crystalline

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Defects analysis of RE : YAG (RE = Nd3+, Er3+) single crystal synthesized by Czochralski method (Czochralski법으로 성장된 RE : YAG(RE = Nd3+, Er3+) 단결정의 결함분석)

  • Park, Cheong Ho;Joo, Young Jun;Kim, Hye Young;Shim, Jang Bo;Kim, Cheol Jin
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.26 no.1
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    • pp.1-7
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    • 2016
  • RE : YAG (RE=Nd3+, Er3+) single crystals are laser diodes and generally grown by Czochralski method with controlling the various growth parameter. Since the defects occurred by temperature gradient or the rotation speed of solid-liquid growth interface act as the decline of crystal optical property during the growth procedure, crystalline quality improvement via defects analysis is necessary. The etch pit density (EPD) analysis was used to confirm the surface defect of grown RE : YAG single crystal and to select the area of transmission electron microscopy (TEM) analysis. Defects in the specimen produced by tripod polishing method such as buckling, rod shaped, bend contours by internal stress, segregation and others were observed by using 200 kV TEM and 300 kV FE-TEM.

Effect of Ni dopant on the multiferroicity of BiFeO3 ceramic

  • Hwang, J.S.;Yoo, Y.J.;Kang, J.H.;Lee, K.H.;Lee, B.W.;Park, S.Y.;Lee, Y.P.
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.139.1-139.1
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    • 2016
  • Multiferroic materials are of great interest because of its potential applications in the design of devices combining magnetic, electronic and optical functionalities. Among various multiferroic materials, BiFeO3(BFO) is known to be one of the intensively focused mainly due to the possibility of multiferroism at device working temperature (> 200C). However, leakage current and weak polarization resulting from oxygen deficiency and crystalline defect should be resolved. Furthermore the magnetic ordering of pure BFO mainly prefers to have antiferromagnetic coupling. Up to now many attempts have been performed to improve the ferromagnetic and the ferroelectric properties of BFO by doping. In this work, we investigated the effects of Ni substitution on the multiferroism of bulk BFO. Four BFO samples (a pure BFO and three Ni-doped BFO's; BiFe0.99Ni0.01O3, BiFe0.98Ni0.02O3 and BiFe0.97Ni0.03O3) were synthesized by the standard solid-state reaction and rapid sintering technique. The XRD results reveal that Ni atoms are substituted into Fe-sites and give rise to phase transition of cubic to rhombohedal. By using vibrating sample magnetometer and standard ferroelectric tester, the multiferroic properties at room temperature were characterized. We found that the magnetic moment of Ni-doped BFO turned out to be maximized for 3% of Ni dopant.

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Scattering characteristics of metal and dielectric optical nano-antennas

  • Ee, Ho-Seok;Lee, Eun-Khwang;Song, Jung-Hwan;Kim, Jinhyung;Seo, Min-Kyo
    • Proceedings of the Korean Vacuum Society Conference
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    • 2015.08a
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    • pp.76.1-76.1
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    • 2015
  • Optical resonances of metallic or dielectric nanoantennas enable to effectively convert free-propagating electromagnetic waves to localized electromagnetic fields and vice versa. Plasmonic resonances of metal nanoantennas extremely modify the local density of optical states beyond the optical diffraction limit and thus facilitate highly-efficient light-emitting, nonlinear signal conversion, photovoltaics, and optical trapping. The leaky-mode resonances, or termed Mie resonances, allow dielectric nanoantennas to have a compact size even less than the wavelength scale. The dielectric nanoantennas exhibiting low optical losses and supporting both electric and magnetic resonances provide an alternative to their metallic counterparts. To extend the utility of metal and dielectric nanoantennas in further applications, e.g. metasurfaces and metamaterials, it is required to understand and engineer their scattering characteristics. At first, we characterize resonant plasmonic antenna radiations of a single-crystalline Ag nanowire over a wide spectral range from visible to near infrared regions. Dark-field optical microscope and direct far-field scanning measurements successfully identify the FP resonances and mode matching conditions of the antenna radiation, and reveal the mutual relation between the SPP dispersion and the far-field antenna radiation. Secondly, we perform a systematical study on resonant scattering properties of high-refractive-index dielectric nanoantennas. In this research, we examined Si nanoblock and electron-beam induced deposition (EBID) carbonaceous nanorod structures. Scattering spectra of the transverse-electric (TE) and transverse-magnetic (TM) leaky-mode resonances are measured by dark-field microscope spectroscopy. The leaky-mode resonances result a large scattering cross section approaching the theoretical single-channel scattering limit, and their wide tuning ranges enable vivid structural color generation over the full visible spectrum range from blue to green, yellow, and red. In particular, the lowest-order TM01 mode overcomes the diffraction limit. The finite-difference time-domain method and modal dispersion model successfully reproduce the experimental results.

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Low temperature synthesis of ZnO nanopowders by the polymerized complex method (착체중합법을 이용한 ZnO 나노분말의 저온합성)

  • 권용재;김경훈;임창성;심광보
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.12 no.5
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    • pp.229-233
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    • 2002
  • Nano-sized ZnO particles were successfully synthesized at low temperatures by a polymerized complex method via an organochemical route. The polymeric precursors could be prepared using Zn nitrate hexahydrate and a mixed solution of citric acid and ethylene glycol as a chelating agent and a reaction medium. The polymeric precursors were calcined at temperatures from 300 to 700C for 3 h, and evaluated for degree of crystallization process, thermal decomposition, surface morphology and crystallite size. The thermal decomposition and crystallization process were analyzed by TG-DTA, FI-IR and XRD. The morphology and crystallite size of the calcined particles were evaluated by scanning electron microscopy (SEM), transmittance electron microscopy (TEM) and Scherrer's equation. Crystallization of the ZnO particles was detected at 300C and entirely completed above 400C. Particles calcined between 400 and 700C showed a uniform size distribution with a round shape. The average particle sizes calcined at 400C for 3 hour were 30~40nm showing an ordinary tendency to increase with the temperatures.

Semiconductor type micro gas sensor for H2 detection using a SnO2Ag2OPtOx system by screen printing technique (스크린 프린팅 기법을 이용한 SnO2Ag2OPtOx계 반도체식 마이크로 수소 가스센서에 관한 연구)

  • Kim, Il-Jin;Han, Sang-Do;Lee, Hi-Deok;Wang, Jin-Suk
    • Journal of Hydrogen and New Energy
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    • v.17 no.1
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    • pp.69-74
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    • 2006
  • Thick film H2 sensors were fabricated using SnO2 loaded with Ag2O and PtOx. The composition that gave the highest sensitivity for H2 was in the weight% ratio of SnO2:PtOx:Ag2O as 93 : 1 : 6. The nano-crystalline powders of SnO2 synthesized by sol-gel method were screen printed with Ag2O and PtOx on alumina substrates. The fabricated sensors were tested against gases like H2, CH4, C3H8, C2H5OH and SO2. The composite material was found sensitive against H2 at the working temperature 130C, with minor interference of other gases. The H2 gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO2Ag2OPtOx system exhibited the high performance, high selectivity and very short response time to H2 at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H2.

Effect of Magnetic Field Annealing on Microstructure and Magnetic Properties of FeCuNbSiB Nanocrystalline Magnetic Core with High Inductance

  • Fan, Xingdu;Zhu, Fangliang;Wang, Qianqian;Jiang, Mufeng;Shen, Baolong
    • Applied Microscopy
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    • v.47 no.1
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    • pp.29-35
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    • 2017
  • Transverse magnetic field annealing (TFA) was carried out on Fe73.5Cu1Nb3Si15.5B7 nano-crystalline magnetic core with the aim at decreasing coercivity (Hc) while keeping high inductance (Ls). The magnetic field generated by direct current (DC) was applied on the magnetic core during different selected annealing stages and it was proved that the nanocrystalline magnetic core achieved lowest Hc when applying transverse field during the whole annealing process (TFA1). Although the microstructure and crystallization degree of the nanocrystalline magnetic core exhibited no obvious difference after TFA1 compared to no field annealing, the TFA1 sample showed a more uniform nanostructure with a smaller mean square deviation of grain size distribution. Hc of the nanocrystalline magnetic core annealed under TFA1 decreased along with the increasing magnetic field. As a result, the certain size nanocrystalline magnetic core with low Hc of 0.6 A/m, low core loss (W at 20 kHz) of 1.6 W/kg under flux density of 0.2 T and high Ls of 13.8μH were obtained after TFA1 with the DC intensity of 140 A. The combination of high Ls with excellent magnetic properties promised this nanocrystalline alloy an outstanding economical application in high frequency transformers.

Characteristics of Pt, Pt-Ru and Pt-CeO2 Catalysts Supported on Carbon Nanotubes for Methanol Fuel Cell (탄소 나노튜브에 담지된 Pt, Pt-Ru 및 Pt-CeO2 메탄올 연료전지 촉매의 특성)

  • Hwang, Gui-Sung;Lee, Rhim-Youl
    • Korean Journal of Materials Research
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    • v.21 no.3
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    • pp.138-143
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    • 2011
  • Nanosized Pt, Pt-Ru and Pt-CeO2 electrocatalysts supported on acid-treated carbon nanotube (CNT) were synthesized by microwave-assisted heating of polyol process using H2Cl6Pt6H2O, RuCl3, CeCl3 precursors, respectively, and were characterized by XRD and TEM. And then the electrochemical activity of methanol oxidation for catalyst/CNT nanocomposite electrodes was investigated. The microwave assisted polyol process produced the nano-sized crystalline catalysts particles on CNT. The size of Pt supported on CNT was 7~12 nm but it decreased to 3~5 nm in which 10wt% sodium acetate was added as a stabilizer during the polyol process. This fine Pt catalyst particles resulted in a higher current density for Pt/CNT electrode. It was also found that 10 nm size of PtRu alloys were formed by polyol process and the onset potential decreased with Ru addition. Cyclic voltammetry analysis revealed that the Pt75Ru25/CNT electrode had the highest electrochemical activity owing to a higher ratio of the forward to reverse anodic peak current. And the chronoamperemetry test showed that Pt75Ru25 catalyst had a good catalyst stability. The activity of Pt was also found to be improved with the addition of CeO2.

GaAs-Carbon Nanotubes Nanocomposite: Synthesis and Field-Emission Property (갈륨비소-탄소나노튜브 복합체 제작과 전계방출특성)

  • Lim, Hyun-Chul;Chandrasekar, P.V.;Chang, Dong-Mi;Ahn, Se-Yong;Jung, Hyuk;Kim, Do-Jin
    • Korean Journal of Materials Research
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    • v.20 no.4
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    • pp.199-203
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    • 2010
  • Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at 400C under an N2/O2 atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from 400C to 600C. The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under 500C, while nanowire structures begin to form on the beads above 600C. The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of 2.0V/μm was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

Characteristics of Ag-added Ge2Sb2Te5 Thin Films and the Rapid Crystallization (Ag-첨가 Ge2Sb2Te5 박막의 물성 및 고속 결정화)

  • Kim, Sung-Won;Song, Ki-Ho;Lee, Hyun-Yong
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.21 no.7
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    • pp.629-637
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    • 2008
  • We report several experimental data capable of evaluating the amorphous-to-crystalline (a-c) phase transformation in (Ag)x(Ge2Sb2Te5)1x (x = 0, 0.05, 0.1) thin films prepared by a thermal evaporation. The isothermal a-c structural phase changes were evaluated by XRD, and the optical transmittance was measured in the wavelength range of 8003000 nm using a UV-vis-IR spectrophotometer. A speed of the a-c transition was evaluated by detecting the reflection response signals using a nano-pulse scanner with 658 nm laser diode (power P = 117 mW, pulse duration t = 10460 ns). The surface morphology and roughness of the films were imaged by AFM. It was found that the crystallization speed was so enhanced with an increase of Ag content. While the sheet resistance of c-phase (Ag)x(Ge2Sb2Te5)1x was similar to that of c-phase Ge2Sb2Te5 (i.e., Rc10Ω/), the sheet resistance of a-phase (Ag)x(Ge2Sb2Te5)1x was found to be lager than that of a-phase Ge2Sb2Te5, Ra5×106Ω/. For example, the ratios of Ra/Rc for Ge2Sb2Te5 and (Ag)0.1(Ge2Sb2Te5)0.9 were approximately 5×105 and 5×106, respectively.

Crystallization and Magnetic Properties of Non-Equilibrium Al(Fe-Cu) Alloy Powders Produced by Rod Milling and Chemical Leaching (Rod Milling과 Chemical Leaching에 의해 제작된 비평형 Al(Fe-Cu) 합금 분말의 결정화 및 자기적 특성)

  • Kim Hyun-Goo
    • Journal of Powder Materials
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    • v.11 no.6 s.47
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    • pp.486-492
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    • 2004
  • We report the crystallization and magnetic properties of non-equilibrium Al0.6(FexCu1x)0.4(x=0.25,0.50,0.75) alloy powders produced by rod-milling as well as by new chemical leaching. X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and vibrating sample magnetometry were used to characterize the as-milled and leached specimens. After 400 h or 500 h milling, only the broad peaks of nano bcc crystalline phases were detected in the XRD patterns. The crystallite size, the peak and the crystallization temperatures increased with increasing Fe. After being annealed at 600C for 1 h for as-milled alloy powders, the peaks of bcc AlCu4andAl13Cu4Fe3forx=0.25,bccAlCu4andAl5Fe2forx=0.50,andAl5Fe2,andAl0.5Fe0.5forx=0.75 are observed. After being annealed at 500and600Cfor 1 h for leached specimens, these non-equi-librium phases transformed into fcc Cu and CuFe2O4phases for the x=0.25 specimen, and into bcc αFe,fccCu,andCuFe2O4 phases for both the x=0.50 and the x=0.75 specimens. The saturation magnetization decreased with increasing milling time for Al0.6(FexCu1x)0.4 alloy powders. On cooling the leached specimens from 800\~850C,\;the magnetization first sharply increase at about 491.4C,745C,and750.0C for x=0.25, x=0.50, and x=0.75 specimens, repectively.