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pISSN : 1225-1429 / eISSN : 2234-5078

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2011, Vol.21, No.5

  • 1.

    Fabrication and characterization of tilted R-plane sapphire wafer for nonpolar a-plane GaN

    강진기 | KIM, YOUNG JIN | 2011, 21(5) | pp.187~192 | number of Cited : 4
    Abstract PDF
    Tilt angle of r-plane wafer is a one of the important factors related with the quality of the GaN epi, so the fine control of the tilt angle is important for the growing of high quality non-polar a-GaN epi. We prepared the R-plane sapphire wafers with slight tilt angles for nonpolar a-plane GaN. The target tilt angles of α and β were 0, −0.1, −0.15,−0.2, −0.4, −0.6o and −0.1, 0, 0.1o, respectively. The tilt angles of sliced R-plane sapphire wafers were measured by x-ray and the statistical evaluation of reliability of tilt angles of wafers were performed. The tolerance of the tilt angle was ± 0.03o. R-plane sapphire wafers have relatively large distributions of BOW and TTV data than c-plane sapphire wafers due to the large anisotropy of R-plane. As the tilt angle α was increased from −0.1 to −0.6o, the step widths and heights were decreased from 156 nm to 26 nm and 0.4 nm to 0.2 nm, respectively. The growth and qualities of GaN epi seems to be largely affected by the change of step structure of R-plane sapphire wafers with tilt angle.
  • 2.

    Finite element analysis for czochralski growth process of sapphire single crystal

    임수진 | 신호용 | 김종호 and 1other persons | 2011, 21(5) | pp.193~198 | number of Cited : 10
    Abstract PDF
    Recently sapphire crystals are used in LED applications. The Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal. A successful growth of perfect single crystals requires the control of heat and mass transport phenomena in the CZ growth furnace. In this study, the growth processes of the sapphire crystal in an inductively heated CZ furnace have been analyzed numerically using finite element method. The results shown that the high temperature positions moved from the crucible surface to inside the melt and the crystalmelt interface changed to the flat shape when the rpm was increased. Also the crystal-melt interface shape has been influenced by the shoulder shape of the grown crystal during the initial stage.
  • 3.

    Crystal growth and transport current properties of cylindrical (YSmNd)- Ba-Cu-O superconductors by zone melt growth method

    So-Jung Kim | Park Jong Kuk | 2011, 21(5) | pp.199~204 | number of Cited : 1
    Abstract PDF
    (YSmNd)1.8Ba2.4Cu3.4O7 − x [(YSN)1.8] high Tc superconductor was directionally grown by zone melt growth process,in air atmosphere. In this study, optimum melting temperature and growth rate were 1100oC and 3.5 mm/hr, respectively. The microstructure of well-textured (YSN)1.8 samples were examined by XRD, optical microscopy, TEM and SQUID magnetometer. The critical current density of these samples were measured by the direct transporting current method. In the observation using an optical microscopy, nonsuperconducting (YSmNd)2BaCuO5[(YSN)211] inclusions of (YSN)1.8 superconductor uniformly distributed within the superconducting (YSmNd)Ba2Cu3Ox[(YSN)123] matrix. The directionally melt-textured (YSN)1.8 superconductor showed an onset Tc ≥ 90 K and sharp superconducting transition. The transport Jc values were 830 A and 3.93 × 104 (A/cm2) at 77 K self-field, respectively.
  • 4.

    Optical properties of Al doped ZnO Nanofibers Prepared by electrospinning

    송찬근 | 윤종원 | 2011, 21(5) | pp.205~209 | number of Cited : 2
    Abstract PDF
    Zinc oxide has semi-conductivity and super conductivity characteristics. It can be used optically and is applied on many areas such as gas sensor, solar cell and optical waveguide. In this paper, to improve optical characteristics of ZnO, aluminum was added on zinc oxide. Zinc oxide and aluminum zinc oxide was fabricated as nano fiber form. ZnO solution was created by mixing poly vinyl pyrrolidone, ethyl alcohol, and zinc acetate. An Al doped ZnO was created by adding aluminum solution to ZnO sol. By applying these sols on electro spinning method, nano fibers were fabricated. These fibers are heat treated at 300, 500, and 700oC degrees and were analyzed with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to examine the nano structures. TGA and DSC measurement was also used to measure the change of mass and calorie upon temperature change. The absorbance of ZnO and Al-doped ZnO was carried out by UV-vis measurement.
  • 5.

    Anti-bacterial effects of the Na2O-TiO2-P2O5 glass-ceramics added Ag+ ion

    No Hyung Park | 유은성 | 2011, 21(5) | pp.210~213 | number of Cited : 0
    Abstract PDF
    Glass-ceramics composed of 5Na2O-36CaO-10TiO2-xP2O5 could be obtained with P2O5 content as following procedure: 1) leaching out Ca3(PO4)2 crystals between Ca3(PO4)2 and NaTi2(PO4)3 selectively in 1 N HCl solution for 2days, and 2) exchanging Na+ ion to Ag+ ion in Ag(NO3) solution for 1 day. Scanning electron microscope (SEM) and Xrat diffractometer (XRD) were measured to verify the proper synthesis of glass-ceramics. And anti-bacteria test was accomplished using Staphylococus aureus bacteria. In the results of anti-bacteria test, the bacteria were died perfectly after 3 hours.
  • 6.

    Effect of strontium ions on K2O-TiO2-SiO2 glass soaked in molten Sr(NO3)2

    No Hyung Park | 유은성 | 이희관 and 1other persons | 2011, 21(5) | pp.214~217 | number of Cited : 0
    Abstract PDF
    A fresnoite glass-ceramics has been investigating considerably because of the second order nonlinearity as well as its permanent optical nonlinearity. However, the chemical compositions of transparent glass-ceramics examined in the previous studies have been limited to adjust the composition close to fresnoite stoichiometrically. In this study, to investigate the effect of strontium ions in glass-ceramics on second order nonlinearity, K2O-TiO2-SiO2 (KTS) glasses soaked in molten Sr(NO3)2 were prepared. Crystalline phases of the soaked glasses were measured by X-ray diffraction (XRD) as soaking times and additional heat treatment. The exchange of strontium ions into the glass was verified by Field Emission Scanning Electron Microscope (FE-SEM). And the phenomena of second order harmonic generation (SHG) was observed using Nd-YAG laser.
  • 7.

    Sintered body characteristics of LAS by addition of CaCO3 and ZrO2 using a solid-state reaction

    김상훈 | EuntaeKang | 김응수 and 2other persons | 2011, 21(5) | pp.218~224 | number of Cited : 1
    Abstract PDF
    LAS (Li2O-Al2O3-SiO2) ceramics were sintered by a solid-state reaction. CaCO3 and ZrO2 were added to the β-spodumene (Li2O-Al2O3-4SiO2) composition of the LAS system for enhancement of sintering behavior and mechanical strength, respectively. We have investigated the sintering characteristics, microstructures, mechanical properties and thermal expansion characteristics according to the change of the amount of additive and sintering temperature of the β-spodumene. At 0.1 mol% CaCO3, the densification of β-spodumene was significantly improved. At 0.04 mol% ZrO2, the strength of β-spodumene was also improved. For all the selected all compositions, the thermal expansion coefficient was measured by a dilatometer, which revealed 1.2 to 1.7 × 10−6/oC.