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pISSN : 1225-1429 / eISSN : 2234-5078

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2011, Vol.21, No.3

  • 1.

    Growth and optical properties for MgGa2Se4 single crystal thin film by hot wall epitaxy

    Moon,Jong-Dae | Kwangjoon Hong | 2011, 21(3) | pp.99~104 | number of Cited : 0
    Abstract PDF
    A stoichiometric mixture of evaporating materials for MgGa2Se4 single crystal thin films was prepared from horizontal electric furnace. The crystal structure of these compounds has a rhombohedral structure with lattice constants a0 =3.953 Å, c0 = 38.890 Å. To obtain the single crystal thin films, MgGa2Se4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 610oC and 400oC, respectively. The crystalline structure of the single crystal thin films was investigated by the double crystal X-ray rocking curve and X-ray diffraction ω-2θ scans. The carrier density and mobility of MgGa2Se4 single crystal thin films measured from Hall effect by van der Pauw method were 6.21 × 1018 cm−3 and 248 cm2/v·s at 293 K, respectively. The optical absorption of MgGa2Se4 single crystal thin films was investigated in the temperature range from 10 K to 293 K. The temperature dependence of the optical energy gap of the MgGa2Se4 obtained from the absorption spectra was well described by the Varshni’s equation, Eg(T) = Eg(0) − (αT2/T + β). The constants of Varshni’s equation had the values of Eg(0) = 2.34 eV, α = 8.80 × 10−4 eV/K and β = 251 K, respectively.
  • 2.

    A study on the brilliance by critical angle of gem and measurement theory of refractive index using refractometer

    문소이 | SEOK, JEONG-WON | 2011, 21(3) | pp.105~109 | number of Cited : 0
    Abstract PDF
    Critical angle of quartz (R.I.≒1.553) and diamond (R.I. = 2.417) are 40.09oand 24.26othat calculated by sinθ = r2/r1 (r = refractive index, r1 > r2). Brilliance of quartz and diamond are 20.33 % and 55.07 %. The brilliance data are result of study on the incident light internal round brilliant cut quartz and diamond by the critical angle. Cause of bow-tie phenomenon can be studied by application of critical angle theory and light path inside fancy shape brilliant cut. When refractormetry with typical gem refractometer, critical angle of quartz and corundum are 59.1oand 77.9o.
  • 3.

    Formation of GaN microstructures using metal catalysts on the vertex of GaN pyramids

    윤위일 | 조동완 | 옥진은 and 6other persons | 2011, 21(3) | pp.110~113 | number of Cited : 1
    Abstract PDF
    In this paper, we propose a new method for the fabrication of GaN microstructures formed only on the vertex of GaN pyramid by using of metal catalysts. GaN pyramidal structures were selectively grown on 3 μm SiO2 dot patterns followed by thin film deposition of Au and Cr only on the vertex area of the GaN pyramids with precisely controlled photolithography. After the metal deposition, the samples were loaded in the MOVPE reactor for the growth of GaN microstructures for 10 minutes. Temperature for the growth of the GaN microstructures was changed from 650oC to 750oC. Rod type GaN microstructures were grown in the direction of vertical to the six {1-101} facets and the shape of the GaN microstructures was changed depend on the type of metal.
  • 4.

    Fabrication of semi-polar nano- and micro-scale GaN structures on the vertex of hexagonal GaN pyramids by MOVPE

    조동완 | 옥진은 | 윤위일 and 7other persons | 2011, 21(3) | pp.114~118 | number of Cited : 0
    Abstract PDF
    We report on the growth and characterization of nano and micro scale GaN structures selectively grown on the vertex of hexagonal GaN pyramids. SiO2 near the vertex of hexagonal GaN pyramids was removed by optimized photolithgraphy process and followed by a selective growth of nano and micro scale GaN structures by metal organic vapor phase epitaxy (MOVPE). The pyramidal GaN nano and micro structures which have crystal facets of semi-polar {1-101} facets were formed only on the vertex of GaN pyramids and the size of the selectively grown nano and micro GaN structures was easily controlled by growth time. As a result of TEM maesurement, Reduction of threading dislocation density was conformed by transmission electron microscopy (TEM) in the selectively grown nano and micro GaN structures. However, stacking faults were newly developed near the edge of SiO2 film because of the roughness and nonuniformity in thickness of the SiO2 film
  • 5.

    The geometry change of carbon nanofilaments by SF6 incorporation in a thermal chemical vapor deposition system

    Kim Sung-Hoon | 2011, 21(3) | pp.119~123 | number of Cited : 2
    Abstract PDF
    Carbon nanofilaments (CNFs) could be synthesized on nickel catalyst layer-deposited silicon oxide substrate using C2H2 and H2 as source gases under thermal chemical vapor deposition system. By the incorporation of SF6 as a cyclic modulation manner, the geometries of carbon coils-related materials, such as nano-sized coil and wave-like nanosized coil could be observed on the substrate. The characteristics (formation density and morphology) of as-grown CNFs with or without SF6 incorporation were investigated. Diameter size reduction for the individual CNFs-related shape and the enhancement of the formation density of CNFs-related material could be achieved by the incorporation of SF6 as a cyclic modulation manner. The cause for these results was discussed in association with the slightly increased etching ability by SF6 addition and the sulfur role in SF6 for the geometry change.
  • 6.

    Fabrication of PLA/TiO2 nanofibers using melt-electro-spinning

    황지영 | KIM HEE JIN | No Hyung Park and 3other persons | 2011, 21(3) | pp.124~128 | number of Cited : 1
    Abstract PDF
    Electrospun webs have been widely investigated for applying to drug delivery system (DDS) because of their high specific surface area and high porosity. In this study, the composite webs of PLA (poly(lactic acid)) and TiO2 were fabricated by melt-electro-spinning method for applying to drug delivery system. The morphologies of PLA/TiO2 webs were observed using scanning electron microscope (SEM) and field emission transmission electron microscope (FE-TEM). The crystal structures of PLA/TiO2 composite webs were confirmed by X-ray diffractometer (XRD).
  • 7.

    Effect of EAF dust on the formation of ultra lightweight aggregates by using bottom ash and dredged soil from coal power plant

    최윤재 | KIM, YOOTAEK | 2011, 21(3) | pp.129~135 | number of Cited : 3
    Abstract PDF
    EAF dust from steel industry used as primary materials for the production of lightweight aggregates. Fe compounds in EAF dust plays an important role in the bloating reaction. This study was conducted to evaluate the feasibility of using bottom ash and dredged soil from coal power plant and EAF dust. The effect of different raw material compositions and sintering temperatures on the lightweight aggregate properties were evaluated. The characteristic of thermal bloating of bottom ash and dredged soil were mainly influenced by ferrous materials. The specific gravity of aggregate was decreased with the addition of EAF dust and kerosene was reduced sintering temperature on the bloating formation. Lightweight aggregate containing 10 % EAF dust having apparent density under 1.0 g/cm 3were produced at 1150~1200oC.