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pISSN : 1225-1429 / eISSN : 2234-5078

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2015, Vol.25, No.5

  • 1.

    Growth and optical conductivity properties for BaIn2S4 single crystal thin film by hot wall epitaxy

    kyunga Jeong | Kwangjoon Hong | 2015, 25(5) | pp.173~181 | number of Cited : 0
    Abstract PDF
    A stoichiometric mixture of evaporating materials for BaIn2S4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, BaIn2S4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 620oC and 420oC, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The carrier density and mobility of BaIn2S4 single crystal thin films measured from Hall effect by van der Pauw method are 6.13 × 1017 cm−3 and 222 cm2/v · s at 293 K, respectively. The temperature dependence of the energy band gap of the BaIn2S4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 3.0581 eV − (3.9511 × 10−3 eV/K)T2/(T + 536 K). The crystal field and the spin-orbit splitting energies for the valence band of the BaIn2S4 have been estimated to be 182.7 meV and 42.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ 5 states of the valence band of the BaIn2S4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C24-exciton peaks for n = 24.
  • 2.

    Selective area growth of micro-sized AlGaN array structures on GaN stripes

    이승현 | Hyung Soo Ahn | Min Yang | 2015, 25(5) | pp.182~187 | number of Cited : 0
    Abstract PDF
    The growth and characterization of micro sized AlGaN array structures selectively grown by metal organic chemical vapor deposition (MOCVD) on GaN stripes are reported. The shape of the AlGaN array structures depends on the size of exposed area for selective growth. The AlGaN array structures grown selectively on relatively large exposed area have regular shapes resembling those of the GaN stripes on the substrate, while samples selectively grown on relatively small exposed area have irregular shapes. The phonon frequency of the AlGaN array structures increases with increasing Al composition in the AlGaN structure. However, at relatively high Al composition (x = 0.28 in this research), the phonon frequency decreases slightly from the expected value not only because of large tensile strain associated with large differences between the lattice constants of the AlGaN structure and underlying GaN stripes but also changes of crystal facet direction during the selective growth.
  • 3.

    Characteristics of gem-quality synthetic diamond from New Diamond Technology in Russia

    Choi, Hyun-min | Young-Chool Kim | 2015, 25(5) | pp.188~192 | number of Cited : 3
    Abstract PDF
    Gemological and spectroscopic properties of HPHT synthetic diamonds from New Diamond Technology (NDT) company in St. Petersburg (Russia) were examined. Their color (colorless, near-colorless with some boron and Fancy blue with high boron content) and clarity (VVS-SI1) grades were comparable to those of top natural diamonds. NDT synthetic diamonds fluoresced and phosphoresced blue or orange under SWUV light. Photoluminescence spectra revealed H3 center with very small intensity and NV centers. The intensity of H3 in NDT synthetic diamond has very weak in comparison with natural one. Using a combination of gemological and spectroscopic tests, gem-quality synthetic diamonds from NDT can be distinguished from natural diamonds of similar quality.
  • 4.

    Preparation of conductive EPDM rubber sheets by electroless Ni-plating for electromagnetic interference shielding applications

    BYEONG WOO LEE | 조수진 | 양준석 | 2015, 25(5) | pp.193~198 | number of Cited : 0
    Abstract PDF
    In the study, electroless Ni-plating on flexible ethylene-propylene-diene-monomer (EPDM) rubber sheets for the application of an insert block for shielding electromagnetic interference of multi cable transit (MCT) systems was investigated. Ni crystallinity and adhesion have been found to vary with processing parameters such as pH and temperature of the plating bath. It was shown that Ni-films having the high crystallinity and optimum electric conductivity were obtained on EPDM rubber sheets under pH 7 and 8 at 60~70oC. The conductive Ni-plated EPDM rubber prepared at pH 7 at 70oC showed the enhanced adhesion and electric conductivity, and the high electromagnetic interference shielding effect in the 400 MHz~1 GHz range.
  • 5.

    Study on the prevention methods of radial cracks generated in artificial lightweight aggregate

    강지민 | Kangduk Kim | KANG SEUNG GU | 2015, 25(5) | pp.199~204 | number of Cited : 0
    Abstract PDF
    In this study, prevention methods of radial cracks generated inside of artificial lightweight aggregate made of reject ash and dredged soil were investigated. The reject ash and dredged soil had mixed with weight ratio of 7 : 3 and formed to spheric shape of 5~20 mm diameter, then, the aggregates were manufactured using flash sintering method at 1200oC for 10 min. The formation of radial cracks in the aggregates were suppressed as the size of specimen decreased. Also, the addition of silica to aggregates had prevented generation of the radial cracks. As the size and the amount of silica powder added increased, the development of radial cracks was constrained. Therefore the artificial lightweight aggregate manufactured in this study expected to be applicable to many fields such as construction and environmental usages. Also it is expected to contribute greatly to increase the recycling rate of reject ash and dredged soil.
  • 6.

    Durability of concrete using sulfur-modified polymer

    Hong, Chang-woo | 2015, 25(5) | pp.205~211 | number of Cited : 1
    Abstract PDF
    Most of the sulfur is obtained from desulfurization of natural gas and crude oil. In Korea, more than 120 tons of sulfur are produced by refinery, and about 50 % of the produced sulfur is used as a raw material for the production of fertilizer and sulfuric acid. Modified sulfur is manufactured from excessive sulfur that could be used to improve concrete properties, and this study evaluated concrete strength and durability that contains modified sulfur. Flexural and compressive strengths of concrete with sulfur modified polymer were comparable to those of OPC concrete with mixing water at similar temperatures, while the strengths increased a little as mixing water temperature increased. It was also confirmed that the resistance to freeze-thaw damage was more dependent on entrained air characteristics obtained by a proper use of air entraining agent than on the use of sulfur modified polymer. When concrete was immersed in 5 % sulfuric acid, the rate of reduction in compressive strength of OPC concrete was less than ¼ of the strength reduction of concrete with sulfur modified polymer. Also, the resistance of concrete with sulfur modified polymer to scaling due to the use of de-icing salt was evaluated as Class 1, while that of OPC concrete was evaluated as Class 4, as aggregates were exposed. Accordingly, it is believed that sulfur modified polymer could be effectively used for bridge deck concrete since sulfur modified polymer improves the durability of concrete.
  • 7.

    Anti-biofouling properties of silver nano-particle coated artificial lightweight aggregates

    김성열 | KIM, YOOTAEK | Park Yong Joon | 2015, 25(5) | pp.212~217 | number of Cited : 1
    Abstract PDF
    Ships and marine structures have a lot of problems in their high maintenance and operating cost by biofouling. A biofouling occurrs by the adhesion of marine microorganism, algae and bacteria. In this study, the aim is to prevent or to reduce the biofouling phenomena through silver nano-particle coating on artificial light-weight aggregates and geopolymer. The antibacterial activity on them is tested according to ASTM E2149-2013a. The test results showed, it is estimated that silver nano-particles removed 99.99 % of bacteria. Specimens were set up in the sea side of field test area in Korea Institute of Ocean Science and Technology (KIOST) and have been observed for five months. The anti-biofouling effect and difference in weight change rate have been detected two months later after the installation. Because silver nanoparticles inhibit bacterial growth and kill the cells by destroying bacterial membranes, silver nano-particle coating on artificial lightweight aggregates is a well-suited and eco-friendly method for preventing biofouling in the sea up to 5 months.
  • 8.

    Study on the control of marine biofouling developed on the surface of porous ceramics

    강지민 | KANG SEUNG GU | KIM, YOOTAEK | 2015, 25(5) | pp.218~224 | number of Cited : 1
    Abstract PDF
    Recently, removing methods of red tide has been attempted by filtering the organisms using the ceramic porous bodies. However, the marine biofouling could be developed on the surfaces of porous ceramic body after use for more than one month, and it might decrease the function of the specimen. In this paper, a method of inhibiting marine biofouling by changing the physical properties or surface-modification of ceramic porous body was studied. After experiment with six different ceramic porous bodies, it was found that the specimen of lower porosity and water absorption showed the least amount of biofouling. In addition, by increasing the surface roughness with silica particles bonded to the surface of specimen, the amount of biofouling caused by large marine life such as barnacle and mussel could be decreased. On the other hand, when the surface of specimen was coated and fused by glass powder, the amount of biofouling was rather increased. This might be due to eluted inorganic ions from the glass which can promote the growth of the microorganism. In conclusion, the environmental-friendly methods to reduce the amount of marine biofouling, such as controlling the physical properties and the surface roughness of the porous ceramics, can be possible without the use of dangerous substances. So it is expected for the results obtained to be applicable to a marine structure.
  • 9.

    Crystal structure of Mn-Co-Ni thermistor

    Lee, Jung-il | 민성욱 | Ryu, Jeong-ho | 2015, 25(5) | pp.225~229 | number of Cited : 0
    Abstract PDF
    This study was performed to investigate crystal structure of cubic spinel-type monophase oxide composed of the Mn-Co-Ni ternary system. Starting material was prepared by mixing Mn, Co, Ni oxides then evaporation to dryness. The XRD patterns were analyzed by in-situ XRD as increasing temperature from room temperature to 1400 o C in air atmosphere. The cubic spinel phase was existed in a temperature range from 900 o C. However, separation of NiO phase was detected from 1300 o C, which was the origin of deterioration in the crytallinity. The surface morphology of the manufactured NTC thermistors were analyzed by FE-SEM for comparison of good and bad samples.