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2009, Vol.19, No.2

  • 1.

    Growth and optical characteristics of the non-phosphor white LED by mixed-source HVPE

    김은주 | 전헌수 | 홍상현 and 9other persons | 2009, 19(2) | pp.61~65 | number of Cited : 0
    Abstract PDF
    In this paper, we report on the growth and optical characteristics of white-LED without fluorescent material. The growth of DH (double heterostructure) with AlGaN active layer was performed on a n-GaN/(0001) Al2O3 by the mixedsource HVPE and multi-sliding boat. The CRI (color rendering index) of packaging device charged in the range 72-93 with CIE chromaticity coordinates (x = 0.26~0.34, y = 0.31~0.40). And CCT (correlated color temperature) values was measured 5126~10406 K with increasing injection current. The CIE point of conventional phosphor white LED shifts blue region, but CIE point of non-phosphor white LED shifts opposite direction. These results show the mixed-source HVPE can be possible to newly fabricate method of phosphor free white LED with high CRI value.
  • 2.

    Preparation and properties of multiferroic bismuth iron oxides

    Nam, Joong-Hee | Cho Jeong Ho | KIM BYUNG IK and 2other persons | 2009, 19(2) | pp.66~69 | number of Cited : 0
    Abstract PDF
    BiFeO3, Canted orthoferrite, Multiferroic oxide, Dielectric dispersion
  • 3.

    Effect of the processing variables on the formation of Pb(Sc1/2Nb1/2)O3 thin layers

    Park Kyung Bong | 권승협 | Tae Heui Kim | 2009, 19(2) | pp.70~74 | number of Cited : 0
    Abstract PDF
    Effect of the processing variables on the formation of Pb(Sc1/2Nb1/2)O3 (hereafter PSN) thin layers prepared on Pt(111)/Ti/SiO2/Si substrates using the sol-gel and the spin coating method has been studied. After each deposition, the coated films were heated at 370oC for 5 min. Then they were finally sintered at temperature range of 600~700oC by RTA(rapid thermal annealing). The final multilayered films showed a (111) preferred orientation. On a while, the layer-bylayer crystallization of multilayered amorphous thin films without the intermediate heating exhibited a (100) preferred orientation. In case of heat treatment in the tube furnace with the heating rate of 4oC/min, (100) and (111) oriented thin layers were formed simultaneously. The microstructure of the deposited films were dense and crack-free with thickness of 300nm, irrespective of the processing variables.
  • 4.

    Control of carrier concentrations by addition of B2O3 in Si-doped vertical gradient freeze (VGF) GaAs single crystal growth

    배소익 | 한창운 | 2009, 19(2) | pp.75~78 | number of Cited : 0
    Abstract PDF
    Si-doped GaAs single crystals were grown by vertical gradient freeze using PBN crucibles. The amount of oxide layer B2O3 in PBN crucible was changed (0~0.2 wt%) and measured the concentration of carriers. The segregation coefficients of Si in GaAs melt decreased rapidly from initial 0.1 to 0.01 as the amount of B2O3 increases. At the same time, concentration of carriers was shown to decrease. It is likely that the reaction between dopant Si and B2O3 in GaAs melt results in the reduction of Si dopants (donor) while increase in the amount of boron (acceptor). The thin layer of B2O3 glass in PBN crucible was proved to be a better way to reduce defect formation rather than the total amount of B2O3.
  • 5.

    The properties of a low expansion glass ceramics of Li2O-Al2O3-SiO2 system

    김복희 | 고정훈 | 남오정 and 2other persons | 2009, 19(2) | pp.79~83 | number of Cited : 0
    Abstract PDF
    The glass-ceramic of the Li2O-Al2O3-SiO2 system was investigated to develop the low thermal expansion materials. The glass of this system was heat treated at 775oC for 2 h for nucleation and subsequently at 825~900 oC for 2 h for crystallization. The crystal structure of the glass-ceramic of this system was a single phase of β-quartz solid solution (LixAlxSi1 − xO2). The thermal expansion of the glass-ceramic showed 4.40 × 10−7~1.33 × 10−6 K−1 between 25~300oC and 1.56 × 10−6~2.53 × 10−6K−1 between 25~800 oC, higher than lower temperature range. The mechanical strength remained almost same at around high 110 MPa with heating temperature changes.
  • 6.

    Nano inclusions in sapphire samples from Sri Lanka

    K. Jaijong | Kim, Young-chool | Choi, Hyun-min and 4other persons | 2009, 19(2) | pp.84~89 | number of Cited : 0
    Abstract PDF
    The turbid/translucent, near colorless (milky) metamorphic sapphire samples from Sri Lanka have been characterized after the heat treatment in N2 at 1650 oC. As-received sapphire specimens became bluish-colored and exhibited more clarity after the heat treatment. It was found that the color change at inclusions zoning region is attributed by the dissolution. As received samples contain the micro/nano inclusions such as rutile (TiO2), ilmenite (FeTiO3), spinel (MgAl2O4)/ulvospinel (Fe2TiO4) and apatite (Ca5(PO4)3), which were dissolved by the heat treatment and form the blue color through Fe2+/Ti4+ charge transferring. The microstructures become different because as the dissolution of apatite (Ca5(PO4)3(OH,F,Cl)) in alumino silicates (Al2SiO5) occurred, resulting in morphological change with the appearance of (Ca, Mg, Al) silicate on the surface. Both as-received and heat treated samples showed the rhombohedral crystal structure of Al2O3.
  • 7.

    Micro-structural defects in ruby samples from Mong Hsu, Myanmar

    P. Maneeratanasarn | P. Wathanakul | Kim, Young-chool and 4other persons | 2009, 19(2) | pp.90~94 | number of Cited : 0
    Abstract PDF
    Mong Hsu rubies from Myanmar were heat treated in oxidizing (oxygen) atmosphere at 1650oC for 1 hour. The investigations of the micro-structural defects in the samples before and after heat treatment have been carried out by the variety of analysis techniques of FTIR, UV-VIS-NIR and SEM-EDS. It was found that after heat treatment the dark blue cores region were disappeared and turned to orange red color with the presence of the dense cloudy brownish colored tiny particles in and near former blue zoning. As-received ruby samples only revealed the presence of FTIR absorption peaks of diaspore, boehmite and O-H stretching, at 1986, 2115 and 3078/3319 cm−1 , respectively. The UV-VIS-NIR absorption of asreceived and heat treated ruby samples similarly showed peaks at 405, 554 and 693 nm associated with Cr3+, but for the same samples, the absorption peak of heat-treated ruby samples at 693 nm was somewhat stronger than that of the untreated ruby samples. Especially the presence of Cr3+ peaks at 659 and 675 nm was found obviously in as-received ruby samples only. The SEM-EDS investigation disclosed the micro-porous defect structures commonly related to the core regions of the untreated ruby samples, which after heat treatment in an oxidizing environment those defect features have been dissolved into the host phase resulting in the lightening or disappearance of the dark coloration of ruby core.
  • 8.

    Structural characteristics of Zachery treated turquoise

    권기란 | 방신영 | 박종완 and 1other persons | 2009, 19(2) | pp.95~101 | number of Cited : 0
    Abstract PDF
    The surface characteristics of Zachery-treated turquoise stones have been studied in detail with a comparison of natural and plastic-impregnated turquoise. The SEM-EDS analysis exhibited that Zachery-treated turquoise was characterized by the uniform distribution of potassium element through the specimen and did not show the sharp crystalline SiO2 facet and boundary phase which are common in natural ore. The potassium element shown in the Zachery-treated turquoise seemed to be occurred during the treatment process for the improvement of durability. The bar-shaped crystals observed in the pore was found to be a feature of Zachery treated turquoise and are expected to influence on their stability and durability, while the pore sizes in turquoise stones depends on the parameter of the treatment procedure.
  • 9.

    Multiple accelerated degradation test and failure analysis for Ni-BaTiO3 MLCCs

    김정우 | 김진성 | Lee, Hee-Soo and 2other persons | 2009, 19(2) | pp.102~105 | number of Cited : 0
    Abstract PDF
    The accelerated life time test of the MLCCs with different BaTiO3 particle sizes were conducted at 150℃, 75 V condition and the effect of BaTiO3 particle size on the breakdown voltage and degradation characteristics of MLCCs was investigated. The MLCCs were prepared by using the BaTiO3 particles having the size of 0.525 μm, 0.555 μm, 0.580 μm and Ni-electrode, respectively. The MLCCs which have the particle size of 0.525 μm, 0.555 μm, and 0.580 μm, respectively were confirmed to meet the standard requirements of X5R (change capacitance within ± 15 % at −55~85℃) by TCC (Temperature Coefficient of Capacitance). The effect of the BaTiO3 particle size on the insulation resistance behavior of MLCCs was confirmed by BDV (Breakdown Voltage) measurements and the cause and degree of degradation of MLCCs were characterized by XPS analysis after the accelerated life test. The MLCCs with 0.525 μm-BaTiO3 showed better insulation resistance and BDV characteristics compare to other MLCCS and XPS analysis revealed that the MLCCs degradation is caused by the NiO peak and BaTiO3 peak decrease