• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.14 no.1
• /
• pp.48-53
• /
• 2001

The crystal structure of ZnS fabricated by gas-liquid phase reaction was refined by the Rietveld program using X-ray diffraction data. The R-weighted pattern (R$\sub$wp/) of ZnS powder was 10.85%. The fraction of HCP phase was closely related with extra amount of H$_2$S gas. The lattice parameters and crystalline size were changed by the relative ratio of multi-phase. The luminescence property of ZnS:Cu, Al green phosphors prepared by conventional methods was good in the range of 91∼94% and 150∼190${\AA}$, respectively. According to the maximum entropy electron density(MEED) methods, any defects in (001) plane of cubic phase were not found. We suggest that both the Rietveld and maximum entropy density methods may be useful tools for studying luminescence mechanism of other phosphors materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.240-243
• /
• 2002

Carbon nitride films have been deposited on Si(100) substrate by a high voltage discharge plasma combined with laser ablation in a nitrogen atmosphere. The films were grown both with and without the Presence of an assisting focused Nd:YAG laser ablation. The laser ablation of the graphite target leads to vapor Plume plasma expending into the ambient nitrogen arc discharge area. X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to identify the binding structure and the content of the nitrogen species in the deposited films. The surface morphology of the films was studied using a scanning electron microscopy Data of infrared spectroscopy and x-ray photoelectron spectroscopy indicate the existence of carbon-nitrogen bonds in the films. The x-ray diffraction measurements have also been taken to characterize the crystal properties of the obtain films.

• Journal of Electrical Engineering and information Science
• /
• v.3 no.1
• /
• pp.110-116
• /
• 1998

A single-crystalline epitaxial film of GaAs has been grown on Si using a gs assisted-ionized vapour beam eptaxial technique. The native oxide layer on the silicon substrate was removed at 550$^{\circ}C$ by use of an accelerated arsenic ion beam, instead of a high-temperature desorption. During the growth the substrate temperature was maintained at 550$^{\circ}C$. Transmission electron microscopy and electron diffraction data suggest that the GaAs layer is an epitaxially grown single-crystalline layer. The possibility of growing device quality GaAs on Si is able demonstrated through fabrication of GaAs MODFET on Si substrates.

• Carbon letters
• /
• v.15 no.2
• /
• pp.113-116
• /
• 2014

Due to their morphology, electrochemical stability, and function as a conducting carbon matrix, graphene nanosheets (GNS) have been studied for their potential roles in improving the performance of sulfur cathodes. In this study, a GNS/sulfur (GNS/S) composite was prepared using the infiltration method with organic solvent. The structure, morphology and crystallinity of the composites were examined using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The electrochemical properties were also characterized using cyclic voltammetry (CV). The CV data revealed that the GNS/S composites exhibited enhanced specific-current density and ~10% higher capacity, in comparison with the S-containing, activated-carbon samples. The composite electrode also showed better cycling performance for multiple charge/discharge cycles. The improvement in the capacity and cycling stability of the GNS/S composite electrode is probably related to the fact that the graphene in the composite improves conductivity and that the graphene is well dispersed in the composites.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.311-316
• /
• 2008

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. The purpose of the present paper is to predict the accurate residual stress of SCM440 high strength steel using the Kendall model which was adopted by ASME Code. Hydraulic pressure process was applied and thick-walled cylinders were autofrettaged up to 30% overstrain levels. Electro polishing was performed to get more accurate data. Residual stresses were measured by X-ray diffraction method. The autofrettaged surface which was plastically deformed analyzed using a scanning electron microscope(SEM). Although there were some differences in measured residual stress and numerical, there is a tendency to agree.

• Proceedings of the KIEE Conference
• /
• 1990.07a
• /
• pp.250-253
• /
• 1990

A single-crystalline epitaxial film of GaAs has been grown on Si using an ionized cluster beam technique. The native oxide layer on the silicon substrate was removed at $550^{\circ}C$ by use of an accelerated arsonic ion beam, instead of a high-temperature desorption. During the growth the substrate temperature was maintained at $550^{\circ}C$. Transmission electron microscopy and electron diffraction data suggest that the eats layer is an epitaxially grown single-crystalline layer.

• Journal of the Mineralogical Society of Korea
• /
• v.11 no.1
• /
• pp.32-44
• /
• 1998

The transformation sequence of kaolinite to mullite is examined with new electron diffraction data obtained mainly by an energy filtering transmission electron microscope. Kaolinite is transformed finally into mullite and cristobalite through several steps of continuous reactions by heating, which result in metakaolinite, microcrystalline spinel-type phase and amorphous silica. Metakaolinite maintains a short-range order in its structure ven at $920^{\circ}C$. Spinel phase results from a topotactictransformation of metakaolinite apart from the breakdown of metakaolinite structure. the first strong exothermic peak on DTA curve is mainly due to the extraction of amorphous silica from metakaolinite and the gradual nucleation of mullite. Metakaolinite decomposes around$ 940^{\circ}C$ to mullite that doesn't show a clear crystallographic relationship to the parent metakaolinite structure. However, spinel phase produced previously is maintained. The initially formed spinel and mullite phases are suggested to be Al-rich, but progressively gain Si in their structures at higher temperatures. Spinel phase decomposes completely through a second weak exothermic reaction promoting the growth of mullite, and crystallization of amorphous silica to cristobalite.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.2
• /
• pp.131-135
• /
• 1992

High-Tc superconducting materials, $HoBa_2Cu_3O_{7-x}F_y$ with $0.0{\leq}y{\leq}0.5$, were synthesized by ceramic method and studied by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, scanning electron microscopy and resistivity measurement. From the X-ray diffraction data, it was found that the samples had only single phase of which lattice volumes were decreased in proportional to the amount of fluorine, which indicated that the relatively small fluorine atoms are effectively substituted for the oxygen sites. Also, an anomalous phenomenon appeared that the peak intensities of (001) planes were greatly increased as fluorine contents increased. SEM photographs revealed that the grain sizes were enlarged progressively with fluorine contents. This fact could be explained along with DTA & TGA data that the incorporation of fluorine gave rise to lowering the melting point. Tc decreased as the incorporation of fluorine content increased. This implies that the superconducting electrons are perturbed due to the substitution of electronegative fluorine atom.

• Journal of the Korean Electrochemical Society
• /
• v.14 no.2
• /
• pp.98-103
• /
• 2011

[ $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ ]cathode material for lithium secondary battery is obtained using co-precipitation method. To determine the optimal metal solution concentration value, the CSTR coprecipitation was carried out at various concentration values(1-2 mol/L). The surface morphology of coated samples was characterization by SEM(scanning electron microscope) and XRD (X-Ray Diffraction)analyses. Impedance analysis and cyclic voltammogram presented that internal resistance of the cell was dependent upon the concentration of metal solution. such data is very helpful in determining the optimal content of metal solution concentration to enhancing electrochemical property by adjusting powder size distribution and crystal structure.

• Journal of the Mineralogical Society of Korea
• /
• v.31 no.2
• /
• pp.103-111
• /
• 2018

Mineralogical properties of two Asian dust (Hwangsa) samples collected during dust events in April 6 and 15, 2018 were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analyses showed that Asian dusts were dominated by phyllosilicates (62 wt%) comprising illite-smectite series clay minerals (ISCMs) (55%), chlorite (3%) and kaolinite (4%). Nonphyllosilicate minerals were quartz (18%), plagioclase (9%), K-feldspar (3%), calcite (3%), and gypsum (2-4%). Mineral compositions determined by SEM chemical analyses were consistent with XRD data. ISCMs occur as submicron grains forming aggregate particles or coating coarse mineral grains such as quartz, plagioclase, K-feldspar, chlorite, and calcite. The ISCMs are often associated with calcite nanofibers and gypsum blades. Mineralogical properties of 2018 dusts were similar to those of previous dusts although clay contents were higher than that of coarse 2012 dust.