• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.163-170
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• 1981

The crystallization of $Li_2O-SiO_2$ system glasses and the effect of phase separtion to crystal nucleation were studied. The crystallization temperatures of various glasses were determined by DTA and glasses were nucleation heat treated at the temperatures ranging from 45$0^{\circ}C$ to 5$25^{\circ}C$. These glasses were thengown at $700^{\circ}C$ to observable size in the optical microscope. Crystal nucleation rates of various glasses were obtained by estimating the number of crystals per unit volume. The main crystal phase of these glasses identified by X-ray diffraction was lithium disilicate ($Li_2O$.$2SiO_2$). It was found that the crystal nucleation rate of glass (19.5% $Li_2P$-80.5% $SiO_2$), the nearest composition to lithium disilicate, was higher than other glasses. The opalescence caused by phase separation was observed in the nucleation heat treated glass (16.3% $Li_2O$-83.7% $SiO_2$). The result from nucleation density measurement of this glass indicated that the nucleation was enhanced during early stage of phase separation. The molphologies of crystals in glasses and crystal growth rate at $600^{\circ}C$ were also discussed.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.480-491
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• 2018

Calcium phosphates (CaP) were prepared by a wet chemical method. Micro-crystalline dicalcium phosphate (DCPD) was precipitated at $37^{\circ}C$ and pH 5.0 using $Ca(OH)_2$ and $H_3PO_4$. The precipitated DCPD solution was kept at $37^{\circ}C$ for 96 h. Artificial bone cement was composed of DCPD, $Ca(H_2PO_4)_2{\cdot}H_2O$ (MCPM), and $CaSO_4{\cdot}1/2H_2O$, $H_2O$ and aqueous poly-phosphoric acid solution. The wet prepared CaP powder was used as a matrix for the bone cement recipe. With the addition of aqueous poly-phosphoric acid, the cement hardening reaction was started and the CaP bone cement blocks were fabricated for the mechanical strength measurement. For the tested blocks, the mechanical strength was measured using a universal testing machine, and the microstructure phase analysis was done by field emission scanning electron microscopy and X-ray diffraction. The cement hardening reaction occurred through the decomposition and recrystallization of MCPM and $CaSO_4{\cdot}1/2H_2O$ added on the surface of the wet prepared CaP, and this resulted in grain growth in the bone cement block.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.365-365
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• 2008

In this work, Ga-doped ZnO (GZO) thin films for NOx gas sensor application were deposited on low temperature co-fired ceramics (LTCC) substrates, by RF magnetron sputtering method. The LTCC substrate is one of promising materials for this application since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.). The LTCC substrates with thickness of 400 pm were fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The structural properties of the fabricated GZO thin films with different thickness are analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The GZO gas sensors are tested by gas measurement system under varing operation temperature and show good performance to the NOx gas in sensitivity and response time.

• Membrane and Water Treatment
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• v.6 no.3
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• pp.251-262
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• 2015

In this work the preparation and characterization of a membrane containing a uniform mesoporous Titanium oxide top layer on a porous stainless steel substrate has been studied. The 316 L stainless steel substrate was prepared by powder metallurgy technique and modified by soaking-rolling and fast drying method. The mesoporous titania membrane was fabricated via the sol-gel method. Morphological studies were performed on both supported and unsupported membranes using scanning electron microscope (SEM) and field emission scanning microscope (FESEM). The membranes were also characterized using X-ray diffraction (XRD) and $N_2$-adsorption / desorption measurement (BET analyses). It was revealed that a defect-free anatase membrane with a thickness of $1.6{\mu}m$ and 4.3 nm average pore size can be produced. In order to evaluate the performance of the supported membrane, single-gas permeation experiments were carried out at room temperature with nitrogen gas. The permeability coefficient of the fabricated membrane was $4{\times}10^{-8}\;lit\;s^{-1}\;Pa^{-1}\;cm^{-1}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.4
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• pp.157-164
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• 2003

$LaF_{3}$ thin films have been fabricated on Si (100) substrates under the highest possible vacuum condition by pulsed laser deposition (PLD) method. The temperature of the sbustrate varied from $20^{\circ}C$ to $800^{\circ}C$. The films deposited at the higher temperature indicated the sharper peaks in the X-ray diffraction measurement. A highly oriented film was successfully obtained at a substrate temperature of $800^{\circ}C$. The surface observation by the AFM revealed that the many hexagonal structures constructed the film. The XPS analysis revealed that the lacking of F in the film deposited at $600^{\circ}C$ were much more than that in film at $^20{\circ}C$. Adding the adequate amount of $CF_{4}$ gas in the growth chamber can compensate this lacking of F.

• Advances in materials Research
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• v.4 no.4
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• pp.193-205
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• 2015

Contamination by bacterial strands is a major problem after bone replacement surgeries, so there is a great need to develop low cost biocompatible antibacterial bioactive scaffolds to be used in bone tissue engineering. For this purpose, nano-zinc doped hydroxyapatite with different zinc-concentrations (5, 10 and 15 mol%) was successfully prepared by the wet chemical precipitation method. The prepared powders were used to form porous scaffolds containing biodegradable Ca-cross-linked alginate (5%) in order to enhance the properties of alginate scaffolds. The scaffolds were prepared using the freeze-gelation method. The prepared powders were tested by X-ray diffraction; transmission electron microscope and Fourier transform infrared analyses, while the prepared scaffolds were investigated by Fourier transform infrared analyses, thermogravimetric analyses and measurement of the antibacterial properties. Best results were obtained from scaffold containing 15% mol zinc-doped hydroxyapatite powders and 5% alginate concentration with ratio of 70:30.

• Macromolecular Research
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• v.11 no.5
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• pp.357-367
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• 2003

The linear low density polyethylene (LLDPE)/zeolite composite using novel inorganic filler, zeolite, is prepared by a conventional compounding procedure using a twin-screw extruder. The observed scanning electron microscopic (SEM) morphology shows a good dispersion and adhesion of zeolite in the LLDPE matrix. The mechanical properties in terms of the Young's modulus, the yield stress, the impact strength, and the elongation at break were enhanced with a successive increment of zeolite content up to 40 wt%. The X-ray diffraction measurement is of supportive for the improved mechanical properties and the complex melt viscosity is as well. Upon applying a certain level of strain on the composites, the dewetting, the air hole formation and its growth are characterized. The dewetting originates around the filler particles at low strain and induces elliptical micropores upon further stretching. The microporosity such as the aspect ratio, the number and the total area of the air holes is also characterized. Thus, the composites loaded 40 % zeolite and 300 % elongation may be applicable for breathable microporous films with improved modulus, impact and yield stress, elongation at break, microporosity and air hole properties.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.97-101
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• 2005

ZnO thin films were grown at different plume-substrate (P-S) angles of 90$^{\circ}$ (on-axis PLD), 45$^{\circ}$ and 0$^{\circ}$ (off-axis PLD) using pulsed laser deposition. The x-ray diffraction pattern exhibiting a dominant (002) and a minor (101) peak of ZnO indicates all films were strongly c-axis oriented. By observing of (002) peak, the FWHMs of ZnO (002) peaks decreased and c-axis lattice constant approached the value of bulk ZnO as P-S angle decreased. Whereas the carrier concentration of ZnO thin film deposited at P-S angle of 90$^{\circ}$ was ~ 10$^{19}$ /cm$^{3}$, the Hall measurement of ZnO thin films deposited at P-S angles of 0$^{\circ}$ and 45$^{\circ}$ was impossible due to the decrease of the carrier concentration by the improvement of stoichiometry and crystalline quality. By decreasing P-S angle, the grain size of the films and the UV intensity investigated by photoluminescence (PL) increased and UV peak position showed red shift. The improvement of properties in ZnO thin films deposited by off-axis technique was due to the decrease of repulsive force between a substrate and the particle in plume and the relaxation of supersaturation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1976-1981
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• 2009

Transparent conducting aluminum-doped zinc oxide (AZO) thin films were deposited on Coming glass substrate using an Gun-type rf magnetron sputtering deposition technology. The AZO thin films were fabricated with an AZO ceramic target (Zn: 98wt.%, $Al_2O_3$: 2wt.%). The AZO thin films were deposited with various growth conditions such as the substrate temperature, oxygen pressure. X -ray diffraction (XRD), UV/visible spectroscope, atomic force microscope (AFM), and Hall effect measurement system were done in order to investigate the properties of the AZO thin films Among the AZO thin films prepared in this study, the one formed at conditions of the substrate temperature $100^{\circ}C$, Ar 50 sccm, $O_2$ 5 sccm and working pressure 5 motor showed the best properties of an electrical resistivity of $1.763{\times}10^{-4}\;[{\Omega}{\cdot}cm]$, a carrier concentration of $1.801{\times}10^{21}\;[cm^{-3}]$, and a carrier mobility of $19.66\;[cm^2/V{\cdot}S]$, which indicates that it could be used as a transparent electrode for thin film transistor and flat panel display applications.

• Journal of Electrical Engineering and Technology
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• v.4 no.1
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• pp.118-122
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• 2009

Organic thin film transistors with a pentacene active layer and various polymer gate insulators were fabricated and their performances were investigated. Characteristics of pentacene thin film transistors on different polymer substrates were investigated using an atomic force microscope (AFM) and x-ray diffraction (XRD). The pentacene thin films were deposited by thermal evaporation on the gate insulators of various polymers. Hexamethyldisilazane (HMDS), polyvinyl acetate (PVA) and polymethyl methacrylate (PMMA) were fabricated as the gate insulator where a pentacene layer was deposited at 40, 55, 70, 85, 100 oC. Pentacene thin films on PMMA showed the largest grain size and least trap concentration. In addition, pentacene TFTs of top-contact geometry are compared with PMMA and $SiO_2$ as gate insulators, respectively. We also fabricated pentacene TFT with Poly (3, 4-ethylenedioxythiophene)-Polysturene Sulfonate (PEDOT:PSS) electrode by inkjet printing method. The physical and electrical characteristics of each gate insulator were tested and analyzed by AFM and I-V measurement. It was found that the performance of TFT was mainly determined by morphology of pentacene rather than the physical or chemical structure of the polymer gate insulator