Korean | English

pISSN : 1225-1429 / eISSN : 2234-5078

2020 KCI Impact Factor : 0.17
Home > Explore Content > All Issues > Article List

2009, Vol.19, No.4

  • 1.

    GaN epitaxy growth by low temperature HVPE on CoSi2 buffer/Si substrates

    HA, JUN SEOK | 박종성 | Song Ohsung and 2other persons | 2009, 19(4) | pp.159~164 | number of Cited : 0
    Abstract PDF
    We fabricated 40 nm-thick cobalt silicide (CoSi2) as a buffer layer, on p-type Si(100) and Si(111) substrates to investigate the possibility of GaN epitaxial growth on CoSi2/Si substrates. We deposited GaN using a HVPE (hydride vapor phase epitaxy) with two processes of process I (850 o C-12 minutes + 1080 o C-30 minutes) and process II (557 o C-5 minutes + 900 o C-5 minutes) on CoSi2/Si substrates. An optical microscopy, FE-SEM, AFM, and HR-XRD (high resolution X-ray diffractometer) were employed to determine the GaN epitaxy. In case of process I, it showed no GaN epitaxial growth. However, in process II, it showed that GaN epitaxial growth occurred. Especially, in process II, GaN layer showed selfaligned substrate separation from silicon substrate. Through XRD ω-scan of GaN <0002> direction, we confirmed that the combination of cobalt silicide and Si(100) as a buffer and HVPE at low temperature (process II) was helpful for GaN epitaxy growth.
  • 2.

    Characterization of ruby single crystal grown by PbO-B2O3 flux

    조민희 | 서진교 | Jong-Wan Park and 1other persons | 2009, 19(4) | pp.165~171 | number of Cited : 1
    Abstract PDF
    In this study, ruby single crystals were successfully grown by flux method using an alumina crucible. The alumina crucible can be a substitute for the platinum crucible of high price. The ruby single crystals were grown in the temperature range of 915~1350℃ for 240 h, using PbO-B2O3 mixture. The grown ruby crystals with 9.02 × 6.36 mm in size exhibited red color and were transparent. The optical and structural properties were examined by UV-VIS spectrometry, FTIR and XRD. The optical properties of theses crystals were similar to those of the natural ruby and synthetic ruby grown by other methods.
  • 3.

    Effects of thermal boundary conditions and microgravity environments on physical vapor transport of Hg2Cl2-Xe system

    Geug-Tae Kim | Moo Hyun Kwon | Kyong-Hwan Lee | 2009, 19(4) | pp.172~183 | number of Cited : 4
    Abstract PDF
    For the effects of the nonlinear temperature profiles and reduced-gravity conditions we conduct a two-dimensional numerical modeling and simulations on the physical vapor transport processes of Hg2Cl2 -Xe system in the horizontal orientation position. Our results reveal that: (1) A decrease in aspect ratio from 5 to 2 leads to an increasingly nonuniform interfacial distribution and enhances the growth rate by one-order magnitude for normal gravity and linear wall temperature conditions. (2) Increasing the molecular weight of component B, Xenon results in a reduction in the effect of solutal convection. (3) The effect of aspect ratio affects the interfacial growth rates significantly under normal gravity condition rather than under reduced gravitational environments. (4) The transition from the convection-dominated regime to the diffusion-dominated regime ranges arises near at 0.1g0 for operation conditions under consideration in this study.
  • 4.

    A study on the growth behavior of nano NiO crystals synthesized by a solid state reaction

    Kim Chang Sam | Kang, Seung-Min | 정덕수 | 2009, 19(4) | pp.184~189 | number of Cited : 2
    Abstract PDF
    We characterized the growth behavior of nano NiO crystals synthesized by heat-treatment in air at the elevated temperatures using nickel nitrate (Ni(NO3)2·6H2O). The crystals had the octahedral shape and the length of 200~500 nm. The truncation was observed when the NiO powder was heated up to 900℃for 2 hours. but not be seen at under 600℃It was observed that nano NiO crystals synthesized at 900℃made up the networks, the coalescence of the nano crystals through the neck formation between the crystals appeared as the first stage in the sintering mechanism.
  • 5.

    Synthetic and characterization of Na-tetrasilicic fluorine mica by skull melting method

    SEOK, JEONG-WON | Choi Jong Keon | 2009, 19(4) | pp.190~195 | number of Cited : 0
    Abstract PDF
    Na-tetrasilicic fluorine mica powders were synthesized by skull melting method. The staring materials having chemical composition of Mg3(OH)2Si4O10 : Na2SiF6 : SiO2 = 8.3 : 24.8 : 66.9 mol% were charged into a cold crucible of 13 cm in diameter and 14cm in height and heated by R.F. generator at working frequency of 2.84 MHz. The materials were maintained for 1hr as a molten state and cooled down in the container. In this study, the specific electric resistance of mica was estimated and the columnar and plate shaped mica were synthesized.
  • 6.

    Synthesis, photoluminescence and thermal properties of laponite-X (X = Eu, Tb) phosphors

    김표라 | Kim Youhyuk | 손동민 and 1other persons | 2009, 19(4) | pp.196~201 | number of Cited : 2
    Abstract PDF
    In order to give emission functionality for laponite the laponite-X (X = Eu, Tb) phosphors were prepared by calcination of cryogels which were prepared through Na ion exchange reaction with Eu and Tb ions. Thermal stability and emission properties of new laponite-X (X = Eu, Tb) phosphors were investigated by X-ray diffractormeter and UV/VUV spectrofluorometer. The phosphors were stable around up to 600℃and new crystalline phases were observed at 700℃. Red and green emissions of phosphors under UV/VUV excitation were also identified at 300℃and 500℃as emission peaks of Eu3+ and Tb3+, respectively.
  • 7.

    Synthesis of Fe/Al2O3 and Fe/TiO2 nanocomposite powder by mechanical alloying

    이성희 | Lee Chung-Hyo | 2009, 19(4) | pp.202~207 | number of Cited : 0
    Abstract PDF
    Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the Fe3O4-M (M = Al, Ti), where pure metals are used as reducing agent. It is found that Fe/Al2O3 and Fe/TiO2 nanocomposite powders in which Al2O3 and TiO2 are dispersed in α-Fe matrix with nano-sized grains are obtained by MA of Fe3O4 with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in Fe/Al2O3 is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of α-Fe in Fe/TiO2 nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solidstate reduction of magnetite by pure metals during MA.
  • 8.

    A study on the surface modification of artificial lightweight aggregates by using bottom ash from coal power plant

    류유광 | KIM, YOOTAEK | 2009, 19(4) | pp.208~213 | number of Cited : 4
    Abstract PDF
    Artificial lightweight aggregates were produced by using bottom ashes and dredged soils from coal power plant. The amount of glassy phases on the aggregate surfaces, specific gravities, absorption rates, and observations of crosssectional surfaces were compared according to the compositions, sintering temperatures, and the amount of coating. It is concluded that surface modification by 10 % CaCO3 coating on the aggregate surfaces enhances the properties of aggregates as follows: Specific gravities were controlled by depressing formation of large pores in the aggregates. Sticking phenomena among aggregates during the sintering process was drastically decreased by reducing glassy phases on the aggregate surfaces. Pumping problems during the application of ready-mix concretes containing lightweight aggregates having high value of absorption rates could be solved by reducing the absorption rate.