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2009, Vol.19, No.1

  • 1.

    Growth of semi-polar (1-101) InGaN/GaN MQW structures on 8o off -axis (100) patterned Si substrate by MOVPE

    한영훈 | 전헌수 | 홍상현 and 9other persons | 2009, 19(1) | pp.1~5 | number of Cited : 0
    Abstract PDF
    In this study, we performed growth of InGaN/GaN multi quantum well (MQW) structures on semi-polar (1-101) GaN facet on 8-degree off oriented stripe patterned (100) Si substrates by MOVPE. The structural and optical properties of the InGaN/GaN multi quantum well (MQW) structures grown on (1-101) GaN stripe depend on NH3 flow rate, TMI flow rate and growth temperature are characterized by cathodoluminescence (CL) and scanning electron microscopy (SEM). With the decrease of NH3 flow rate, the threading dislocation of (1-101) GaN is considerably reduced. We could control the transition wavelength of InGaN/GaN MQW structures from 391.5 nm to 541.2 nm depend on the growth conditions.
  • 2.

    Characteristics of selective area growth of GaN/AlGaN double heterostructure grown by hydride vapor phase epitaxy on r-plane sapphire substrate

    홍상현 | 전헌수 | 한영훈 and 7other persons | 2009, 19(1) | pp.6~10 | number of Cited : 1
    Abstract PDF
    In this paper, a selective area growth (SAG) of a GaN/AlGaN double heterostructure (DH) has been performed on r-plane sapphire substrate by using the mixed-source hydride vapor phase epitaxy (HVPE) with multi-sliding boat system. The SAG-GaN/AlGaN DH consists of GaN buffer layer, Te-doped AlGaN n-cladding layer, GaN active layer, Mgdoped AlGaN p-cladding layer, and Mg-doped GaN p-capping layer. The lectroluminescence (EL) characteristics show an emission peak of wavelength, 439 nm with a full width at half maximum (FWHM) of approximately 0.64 eV at 20 mA. The I-V measurements show that the turn-on voltage of the SAG-GaN/AlGaN DH is 3.4 V at room temperature. We found that the mixed-source HVPE method with a multi-sliding boat system was one of promising growth methods for III-Nitride LEDs.
  • 3.

    Crystal growth and optical properties of Zn and Yb co-doped LiNbO3 rod-shape single crystal by micro-pulling down method

    허지윤 | Hojune Lee | Yoon Dae Ho | 2009, 19(1) | pp.11~14 | number of Cited : 0
    Abstract PDF
    Yb and Zn co-doped LiNbO3 single crystal rods which had a diameter of 2 mm and a length of 15~25 mm were grown by micro-pulling down (μ-PD) method. The single crystals were successfully grown and had a uniform diameter and a smooth surface without crack. We realized of LiNbO3 single crystals were hexagonal structure to compare with peaks of LiNbO3 powder by Raman spectra. The threshold level of Zn concentration which is effective for optical damage were observed as about 1 mol% with IR transmission spectra.
  • 4.

    Luminescence characterization of Eu3+ and Bi3+ co-doped in Y2SiO5 red emitting phosphor by solid state reaction method

    문지욱 | 송영현 | 박우정 and 1other persons | 2009, 19(1) | pp.15~18 | number of Cited : 2
    Abstract PDF
    To enhance near UV-visible absorption region and to applied phosphor convert-white LEDs (PC-WLEDs), a red phosphor composed of Y2SiO5: Eu 3+, Bi3+ compounds was prepared by the conventional solid-state reaction. The photoluminescence (PL) shown that samples were excited by near UV light 395 nm for measurement of PL spectra.Emission spectra of samples have shown red emissions at 612 nm (5D0→7F2). The enhanced near UV~ visible excitation spectrum with a broad band centered at 258 nm and 282 nm originated in the transitions toward the charge transfer state (CTS) due to the Eu3+-Bi3+-O2−interaction. The other excitation band at 350 nm~480 nm, corresponding to the transitions 7F0→5L9 (364 nm),7F0→5G3 (381 nm),7F0→ 5L6 (395 nm),7F0→5D3 (415 nm) and 7F0→5D2 (466 nm), occurred due to enhanced the f-f transition increasing Bi3+ and Eu3+ ions. The PL intensity increased with increased as concentration of Bi3+ and the emission intensity becomes with a maximum at 0.125 mol.
  • 5.

    Apatite formation on the surface treated-titanium plate in a simulated body fluid

    이창훈 | 진형호 | PARK,HONG-CHAE and 1other persons | 2009, 19(1) | pp.19~24 | number of Cited : 1
    Abstract PDF
    The purpose of this study was to investigate the formation of apatite layer on two different titanium substrate treated with biomimetic method. Titanium plates were heat-treated at different temperatures of 400oC, 600oC, and 800oC for 5 h in air atmosphere. And then, that plates were chemically treated with an alkali solution of 1M sodium hydroxide(NaOH). The pre-treated titanium plates were soaked in the simulated body fluid (SBF) of Kokubo's recipe. After soaking for 7 days and 21 days in SBF, the coated layers formed on the titanium plates were characterized and compared with the morphology and chemical composition. The apatite formation was more activated on the titanium plates chemically treated with NaOH compared with the only heat-treated titanium plates.
  • 6.

    Microstructural analysis of coal bottom ash-Na2O-Li2O system glass-ceramics

    KANG SEUNG GU | 2009, 19(1) | pp.25~32 | number of Cited : 1
    Abstract PDF
    The glass-ceramics composed of coal bottom ash produced from a thermal power plant, Na2O and Li2O as a flux agent and TiO2 as a nucleation agent were fabricated and its microstructures were analyzed. The nepheline was a major crystal phase in the glass-ceramics fabricated and its amount increased with TiO2 addition. The glass-ceramics without TiO2 addition had the thick surface crystals induced by a surface-crystallization mechanism and no crystal in the interior matrix. The surface crystallization, however, was restrained and the interior matrix was completely crystallized showing dendrite shape spread with fine particles < 1 μm when added with TiO2 above 4 wt%. For the glass-ceramics containing 6 wt% TiO2, the 5 μm-long dendrite crystals were interlocked each other which could suppress the crack propagation effectively at the external loading applied.
  • 7.

    Microstructure and thermal conductivity of AlN ceramics with Y2O3 fabricated by pressureless sintering

    채재홍 | 박주석 | 안종필 and 1other persons | 2009, 19(1) | pp.33~38 | number of Cited : 2
    Abstract PDF
    The effect of Y2O3 as a sintering additive on thermal conductivity and microstructure of pressureless sintered AlN ceramics was investigated at sintering temperature range from 1,700 to 1,900oC. Y2O3 added AlN specimens showed higher densification rate than pure AlN because of the formation of the yttrium aluminates secondary phase by reaction of Y2O3 and Al2O3 of AlN surface. The thermal conductivity of AlN specimens was promoted by the addition of Y2O3 in spite of the formation of secondary phase in AlN grain boundaries and grain boundary triple junction, because Y2O3 addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. The thermal conductivity of AlN specimens was promoted by increasing sintering time because the increases of average grain size and the elimination of secondary phases from the grain boundary due to the evaporation. Particularly, the thermal conductivity of AlN specimen sintered at 1,900oC for 5 hours improved over 20 %, 141Wm−1K−1, compared with the specimen sintered at 1,900oC for 1 hour.
  • 8.

    Generic studies on thermo-solutal convection of mercurous chloride system of Hg2Cl2 and Ne during physical vapor transport

    Jeong-Gil Choi | Kyong-Hwan Lee | Geug-Tae Kim | 2009, 19(1) | pp.39~47 | number of Cited : 6
    Abstract PDF
    The effects of thermo-solutal convection on mercurous chloride system of Hg2Cl2 and Ne during physical vapor transport are numerically investigated for further understanding and insight into essence of transport phenomena. For 10 K ≤ΔT ≤ 30 K, the growth rate slowly increases and, then is decreased gradually until ΔT = 50 K. The occurrence of this critical point near at ΔT = 30 K is likely to be due to the effects of thermo-physical properties stronger than the temperature gradient corresponding to driving force for thermal convection. For the range of 10 Torr ≤ PB≤ 300 Torr, the rate is second order-exponentially decayed with partial pressures of component B, PB. For the range of 5 ≤ MB≤ 200, the rate is second order-exponentially decayed with a function of molecular weight of component B, MB. Like the case of a partial pressure of component B, the effects of a molecular weight are reflected through the binary diffusivity coefficients, which are intimately related with suppressing the convection flow inside the growth enclosure, i.e., transition from convection to diffusion-dominant flow mode as the molecular weight of B increases. The convective mode is near at a ground level, i.e.,on earth (1 g0), and the convection is switched to the diffusion mode for 0.1 g0≤ g ≤ 10−2g0, whereas the diffusion region ranges from 10−2g0 up to 10−5 g0.
  • 9.

    Dependence of physical properties of artificial lightweight aggregates upon a flux and a bloating agent addition

    KANG SEUNG GU | 2009, 19(1) | pp.48~53 | number of Cited : 4
    Abstract PDF
    The effect of bloating and fluxing agent on the microstructure and physical properties were studied in manufacturing the artificial lightweight aggregates of bulk density below 1 using clay and stone sludge. In case of the aggregates added only with bloating agent, the bulk density and water absorption were 0.5~1.0 and 41~110 % respectively but the microstucture was not uniform with a rough appearance. For the aggregates added with a fluxing agent and one bloating agent, a part of shell was lost due to explosion of specimen caused by over-bloating during a sintering. The mixed addition of bloating agents with vacuum oil, carbon and Fe2O3 made the microstructure homogeneous by generating an uniform black core and shell structure. The aggregates added with mixed agents and sintered at 1200oC showed the bulk density 67 % lower and water absorption 48 times higher than those of the specimen with no additives. In this study, the artificial lightweight aggregates showing the bulk density of 0.5~1.0 and water absorption of 50~125 % could be fabricated to apply to various fields.
  • 10.

    Characteristics of artificial lightweight fine aggregates manufactured by using a vertical fluidizing furnace

    KANG SEUNG GU | 2009, 19(1) | pp.54~59 | number of Cited : 0
    Abstract PDF
    It was difficult for the existing rotary kiln to fabricate the fine aggregates under 3 mm due to the sticking phenomenon between specimens. In this study, the vertical type fluidizing furnace was designed and manufactured by which the lightweight fine aggregates of specific gravity 1.1~1.7, water absorption 11~19 % could be fabricated from the green body of clay : stone sludge : spent bleaching clay = 60 : 30 : 10 (wt%) without sticking-together happening. The minimum sintering temperature for bloating of aggregates was 1130oC. The specimens sintered over 1140oC showed the typical bloating characteristics of lightweight aggregates and an inner layer was discovered due to widened cracks on a surface. But the crack on a surface did not propagate into a black core area so had no effect on a water absorption of aggregates. The sintering temperature made the thickness of shell and the black core area thin and expanded respectively but the sintering time did not affect the microsturcture of aggregates. The water absorption of aggregates decreased with increasing temperature owing to increased amount of liquid formed on a surface. Also sintering time affected a lot on a water absorption because it takes a time to form a liquid, which change the open pores to closed pores by blocking.