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pISSN : 1225-1429 / eISSN : 2234-5078

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2004, Vol.14, No.5

  • 1.

    Crystal growth and optical properties with preheating temperature of solgel derived ZnO thin films

    KIM, YOUNG SUNG | SUH, SUJEONG | SONG YONG JIN and 4other persons | 2004, 14(5) | pp.187~192 | number of Cited : 0
    Abstract PDF
    We try to use isopropanol which has low boiling point to prepare ZnO thin films at low temperature. ZnO thin films were prepared by sol-gel spin-coating method using zinc acetate dehydrate-isopropanol-monoethanolamine (MEA) solution. The c-axis preferred orientation and optical properties of ZnO films with preheating temperature have been investigated. ZnO thin films were preheated at 200 to 300oC with an interval of 25oC and post-heated at 650oC. The ZnO film preheated at 275oC and post-heated at 650oC was highly oriented along c-axis (002) plane, and the surface with homogeneous and dense microstructures was formed having nano-sized grains. The optical transmittance was above 90 % in the visible range and exhibited absorption edges at 368 nm wavelength.
  • 2.

    Growth and magnetic properties of Tb, Eu, EuTb-substituted garnet singlecrystal films

    김근영 | Ilsub Chung | Yoon Dae Ho and 2other persons | 2004, 14(5) | pp.193~198 | number of Cited : 0
    Abstract PDF
    Using the PbO-B2O3-Bi2O3 flux system, (TbBi)3(FeAlGa)5O12 (TbIG), (EuBi)3(FeAlGa)5O12 (EuIG) and (EuTbBi)3(FeAlGa)5O12 (EuTbIG) films were grown on (GdCa)3(GaMgZr)5O12 (SGGG) substrates by the liquid phase epitaxy (LPE). The saturation magnetization of the grown TbIG, EuIG and EuTbIG films was about 150, 950 and 125 Oe, respectively. The TbIG films resulted in the single magnetic domain while the EuIG and EuTbIG films were observed to be the multi magnetic domains by magnetic force microscope (MFM).
  • 3.

    Hertzian contact fatigue of dental ceramic implant abutment

    DeukYong Lee | 2004, 14(5) | pp.199~203 | number of Cited : 0
    Abstract PDF
    Feasibility of 3Y-TZP for dental implant abutment was evaluated under the Hertzian cyclic fatigue by examining the extent of the indentation damage and strength degradation. Fatigue test was conducted at contact loads of 500 to 3000 N and up to 106 cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to 5?05 contact cycles. As load rose, the dramatic reduction in strength was observed when the damage transition from ring to radial crack occurred. The extent of strength degradation was more pronounced in vitro environment probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.
  • 4.

    Synthesis of zeolite with reaction temperature and alkali concentrationfrom coal bottom ash

    전소연 | Ji-whan Ahn | 한기천 | 2004, 14(5) | pp.204~210 | number of Cited : 0
    Abstract PDF
    Though the recycling rate of coal fly ash generated from domestic thermoelectric power plants is gradually increased, at present, the most amount of coal bottom ash is disposed by a landfill instead of recycling. Therefore, to reuse a coal bottom ash as high-value materials the synthesis of zeolite made from a coal bottom ash was investigated in this study. NaP1, hydroxy-sodalite and tobermorite were produced through the alkaline hydrothermal reaction of pulverized bottom ash at various temperatures; 80, 120, 150oC, and the concentration of NaOH at the range from 1 to 5 M. Especially, NaP1 with excellent cation exchange capability had a high crystallinity at 2 M NaOH and 120oC.
  • 5.

    Field emission characteristics of carbon nanfiber bundles

    Kim Sung-Hoon | 2004, 14(5) | pp.211~214 | number of Cited : 0
    Abstract PDF
    Carbon nanofiber bundles were formed on silicon substrate using microwave plasma-enhanced chemical vapor deposition system. These bundles were vertically well-grown under the high negative bias voltage condition. The bundles were composed of the individual carbon nanofiber having less than 100 nm diameters. Turn-on voltage of the field emission was measured around 0.8 V/mm. Fowler-Nordheim plot of the measured values confirmed the field emission characteristic of the measured current.
  • 6.

    ZnO film growth on sapphire substrate by RF magnetron sputtering

    Kang, Seung-Min | 2004, 14(5) | pp.215~219 | number of Cited : 0
    Abstract PDF
    ZnO epitaxial films have been grown on a (0001)sapphire substrate by RF magnetron sputtering. The single crystalline ZnO films were grown at the condition of growth rate of about 0.1~0.2 mm/hr and the substrate temperature of 600oC. The film thickness was about 400~500 nm. The thin film quality and micro-structure have been evaluated by XRD and TEM observation.
  • 7.

    High rate dry etching of Si in fluorine-based inductively coupled plasmas

    조현 | S.J. Pearton | 2004, 14(5) | pp.220~225 | number of Cited : 0
    Abstract PDF
    Four different Fluorine-based gases (SF6, NF3, PF5, and BF3) were examined for high rate Inductively Coupled Plasma etching of Si. Etch rates up to ~8 mm/min were achieved with pure SF6 discharges at high source power (1500 W) and pressure (35 mTorr). A direct comparison of the four feedstock gases under the same plasma conditions showed the Si etch rate to increase in the order BF3 < NF3 < PF5 < SF6. This is in good correlation with the average bond energies of the gases, except for NF3, which is the least strongly bound. Optical emission spectroscopy showed that the ICP source efficiently dissociated NF3, but the etched Si surface morphologies were significantly worse with this gas than with the other 3 gases.
  • 8.

    Predictions of zinc selenide single crystal growth rate for the microgravity experiments

    Geug-Tae Kim | 2004, 14(5) | pp.226~232 | number of Cited : 0
    Abstract PDF
    One predicts the crystal growth rate of ZnSe with a low vapor pressure system in a horizontal configuration based on one dimensional advection-diffusion and two-dimensional diffusion-convection model. The present results show that for the ratios of partial pressures, s = 0.2 and 2.9, the growth rate increases with the temperature differences between the source and crystal. As the ratio of partial pressure approaches the stoichiometric value, s = 2 from s = 1.5 (zinc-deficient case: s < 2) and 2.9 (zinc-rich case: s > 2), the rate increases sharply. For the ranges from 1.5 to 1.999 (zinc-deficient case: s < 2) and from s = 9 to 2.9 (zinc-rich case: s > 2), the rate are slightly varied. From the viewpoint of the order of magnitude, the one-dimensional model for low vapor pressure system falls within the 2D predictions, which indicates the flow fields would be advective-diffusive. For the effects of gravitational accelerations on the rate, the gravitational constants are varied from 1 g to 10-6 g for DT = 50 K and s = 1.5, the rates remain nearly constant, i.e., 211 mg/hr, which indicates Stefan flow is dominant over convection.