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pISSN : 1225-1429 / eISSN : 2234-5078

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2014, Vol.24, No.6

  • 1.

    Growth and optical conductivity properties for MnAl2S4 single crystal thin film by hot wall epitaxy method

    You,Sang-Ha | 이기정 | Kwangjoon Hong and 1other persons | 2014, 24(6) | pp.229~236 | number of Cited : 1
    Abstract PDF
    A stoichiometric mixture of evaporating materials for MnAl2S4 single crystal thin films was prepared fromhorizontal electric furnace. To obtain the single crystal thin films, MnAl2S4 mixed crystal was deposited on thoroughlyetched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatureswere 630oC and 410oC, respectively. The crystalline structure of the single crystal thin films was investigated by thephotoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap ofthe MnAl2S4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 3.7920 eV − (5.2729 ×10−4 eV/K)T2/(T + 786 K). In order to explore the applicability as a photoconductive cell, we measured the sensitivity (γ),the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. Theresults indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare within Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of 1.10 × 107, the MAPDof 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.
  • 2.

    Wet chemical etching of molten KOH/NaOH eutectic alloy to evaluate AlN single crystal

    Cheol Woo Park | 홍윤표 | 박재화 and 4other persons | 2014, 24(6) | pp.237~241 | number of Cited : 0
    Abstract PDF
    We investigated the optimal etching conditions and properties of the surface change due to molten KOH/NaOHchemical wet etching using an AlN wafer which has been put to practical use in the present study. Results were observedusing a scanning electron microscope after 5 minutes etching at 350oC, was found to have a surface form of the respectiveother Al-face, the N-face. In particular, etch-pit in the form of a hexagon, which is observed in the Al-face appeared, Itwas calculated at 2 × 106/cm2~1010/cm2dislocation density. In the case of N-face, lattice defects in the form of the hexagonalpyramids is formed. It was discovered that in order to observe the orientation of the wafer, which corresponds to the Caxisdirection of the resulting hexagonal AlN which was analyzed using XRD (0002) and is a state of being oriented inthe (0004) plane. The Radius of curvature of AlN wafer was 1.6~17 m measured by DC-XRD rocking curve position.
  • 3.

    Improvement of uniformity in chemical vapor deposition of silicon carbide using CFD

    서진원 | Jun-Woo Kim | Yoonsoo Han and 2other persons | 2014, 24(6) | pp.242~245 | number of Cited : 1
    Abstract PDF
    In order to increase the thickness uniformity in chemical vapor depositon of silicon carbide, we have carried outCFD studies for a CVD apparatus having a horizontally-rotated 3-stage susceptor. We deposited silicon carbide films of3C-SiC phase showing quite uniform thickness between stages but not uniform one in the stage. The cause of thisnonuniformity is thought to be originated from the high rotational speed. And the uniformity between stages can be furtherincreased with the 120osplit type nozzles from CFD results. Through the formation of silicon carbide film on graphitesubstrates we can make oxidation-resistant and dust-free graphite components with high hardness for the semiconductorapplications.
  • 4.

    Effect of oxygen concentration and oxygen precipitation of the single crystalline wafer on solar cell efficiency

    이송희 | 김성태 | 오병진 and 3other persons | 2014, 24(6) | pp.246~251 | number of Cited : 0
    Abstract PDF
    Recent studies have shown methods of improving solar cell efficiency. Especially on single crystalline siliconwafer which is high-efficiency solar cell material that has been widely studied. Interstitial oxygen (Oi) is the main impurityin the Czochralski (Cz) growing method, and excess of this can form precipitates during cell fabrication. We havedemonstrated the effect of Oi impurity and oxygen precipitation concentration of the wafer on Cz-silicon solar cell efficiency. The result showed a decrease in cell efficiency as Oi and oxygen precipitation increase. Moreover, we have found that thecritical point of [Oi] to bring higher cell efficiency is at 14.5 ppma in non-existent Bulk Micro Defect (BMD).
  • 5.

    Effects of oxygen partial pressure on the properties of indium tin oxide film on PET substrates by RF magnetron sputtering

    김선태 | Taegyu Kim | Cho, Hyun and 1other persons | 2014, 24(6) | pp.252~255 | number of Cited : 0
    Abstract PDF
    Indium tin oxide (ITO) films with various oxygen partial pressure from 0 to 6 × 10−5Pa were prepared ontopolyethylene terephthalate (PET) using RF magnetron sputtering at room temperature. The structural, electrical and opticalproperties of the grown ITO films were investigated as a function of the oxygen partial pressure. The amorphous nature ofthe ITO films was dominant at the partial pressure below 1 × 10−5Pa and the degree of crystallinity increased as theoxygen concentration increased further. This structural change comes with the increased carrier concentration and reductionof the electrical resistivity down to 9.8 × 10−4Ω · cm. The average transmittance (at 400~800 nm) of the ITO deposited onthe PET substrates increased as the oxygen partial pressure increased and transmittance above 80 % was achieved with thepartial pressure of 4 × 10−5Pa. The results show that the choice of optimal oxygen partial pressure can present improvedfilm crystallinity, the increased carrier concentration, and the enhancement in the electrical conductivity.
  • 6.

    Effect of cobalt sulfate contents on the ceramic surface coating using spray technique

    Hyun Park | Kim Kyung Nam | 2014, 24(6) | pp.256~260 | number of Cited : 1
    Abstract PDF
    This study was carried on the phenomena in reactivity with the clay surface according to the thickness of thecobalt component coating. In the coated specimen, it was observed that the cobalt component was spreaded to diffuse witha constant thickness from the surface of it and the diffusion layer at the white porcelain soil was more increased with theincrease of the amount of cobalt sulfate than at the celadon porcelain one. It was evaluated that the color of the surface onthe coated specimen at the white porcelain soil was changed from grayish blue to blue and the L*value was decreasedfrom 51.78 to 37.61 and also in the case of the coated specimen in celadon porcelain soil, L*value was from 53.91 to38.93 and the color was from dark olive gray to dark gray. The physical properties of the specimen were characterized byX-ray diffraction, Scanning electron microscope, Dilatometer, TG-DTA, UV-vis spectrophotometer and HRDPM.
  • 7.

    Manufacture of melting temperature controllable modified sulfur (MS) and its application to MS concrete

    김진희 | JINSUB CHOI | No-Hyung Park | 2014, 24(6) | pp.261~267 | number of Cited : 1
    Abstract PDF
    In this study, we manufactured melting temperature controllable modified surfur (MS) and studied the propertiesof sulfur modified cement concrete (SMC). We investigated the effects of sulfur and pyridine content on meltingtemperature of MS. The reaction is confirmed by measuring Raman spectrophotoscopy. The SMC was produced at Water(W)/Cement (C) = 45 wt%, Sand (S)/Aggregate (A) = 45 wt% and 5, 10, 15 and 20 % of MS on the basis of conventionalportland cement, respectively. And then physical properties such as compressive strength, splitting tensile strength andpermeability of SMC were measured. As MS added, permeability was decreased, while strength and spalling propertieswere improved. To confirm the safety of MS and SMC, pyrolyzed gas chromatography (P-GC) and gas hazard test wereconducted. The results showed that MS and SMC were relatively safe at an elevated temperature.
  • 8.

    Microstructure and plasma resistance of Y2O3 ceramics

    이현규 | 이석신 | 김비룡 and 2other persons | 2014, 24(6) | pp.268~273 | number of Cited : 1
    Abstract PDF
    Y2O3 ceramic specimens were fabricated from the granular powder, obtained by spray drying process from theslurry. The slurry was prepared by mixing PVA binder, NaOH for Ph control, PEG and Y2O3 powder. The Y2O3 specimenwas shaped in size of Ø14 mm and then sintered at 1650oC. The characteristics, microstructure, densities and plasmaresistance of the Y2O3 specimens were investigated with the function of forming pressure and sintering time. Y2O3specimens were exposed under the CHF3/O2/Ar plasma, the dry etching treatment of specimens was carried out by thephysical reaction etching of Ar+ion beam and the chemical reaction etching of F− ion decomposed from CHF3. Withincreasing sintering time, Y2O3 specimens showed relatively high density and strong resistance in plasma etching test.
  • 9.

    A study on the chatter vibration characteristics simulation for cutting tooling of turning machine tool

    Hwang Joon | 2014, 24(6) | pp.274~278 | number of Cited : 1
    Abstract PDF
    Machining performance is often limited by chatter vibration at the tool-workpiece interface. Chatter vibration isa type of machining self-excited vibration which originated from the variation in cutting forces and the flexibility of themachine tool structure. Cutting tooling method is one of major factor to chatter vibration in turning process. Even thoughlots of cutting tooling methods are developed and used in machining process, precise analysis of cutting tooling effect inview of chatter vibration behavior. This study presents numerical and experimental approaches to verify and effects ofvarious cutting tooling geometry and clamping method on the onset of chatter vibration. Acquired knowledge from thisstudy will apply the optimal geometry design of cutting tooling and adjusting of machining process.