• Journal of the Korean Society for Heat Treatment
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• v.33 no.3
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• pp.124-128
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• 2020

Recently, many studies on growth of single crystal diamond using MPECVD have been conducted. The heteroepitaxial method is one of the methods for growing diamonds on a large-area substrate, and research on synthesis of single crystal diamonds using SrTiO₃, MgO, and sapphire substrates has been attempted. In addition, research is being conducted to reduce the internal stress generated during diamond growth and to improve the crystallinity of the diamond. The compressive stress generated therein causes peeling and bowing from the substrate. This study aimed to synthesize heteroepitaxial single crystal diamonds with high crystallinity by surface modification. A diamond thin film was first grown on a sapphire/Ir substrate by MPECVD, and then etched with H₂ gas to modified the morphology and roughness of the surface. A secondary diamond layer was grown on the surface, and the internal stress, crystallinity of the diamond were investigated. As a result, the fabrication of single crystal diamonds with improved crystallinity was confirmed.

• Journal of Powder Materials
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• v.20 no.5
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• pp.376-381
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• 2013

Spherical Ti-6Al-4V powders in the size range of 250 and 300 ${\mu}m$ were uniformly doped with nano-sized hydroxyapatite (HAp) powders by Spex milling process. A single pulse of 0.75-2.0 kJ/0.7 g of the Ti-6Al-4V powders doped with HAp from 300 mF capacitor was applied to produce fully porous and porous-surfaced Ti-6Al-4V implant compact by electro-discharge-sintering (EDS). The solid core was automatically formed in the center of the compact after discharge and porous layer consisted of particles connected in three dimensions by necks. The solid core increased with an increase in input energy. The compressive yield strength was in a range of 41 to 215 MPa and significantly depended on input energy. X-ray photoelectron spectroscopy and energy dispersive x-ray spectrometer were used to investigate the surface characteristics of the Ti-6Al-4V compact. Ti and O were the main constituents, with smaller amount of Ca and P. It was thus concluded that the porous-surfaced Ti-6Al-4V implant compacts doped with HAp can be efficiently produced by manipulating the milling and electro-discharge-sintering processes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.949-956
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• 2007

Pool boiling critical heat flux (CHF) of nanofluids with oxide nanoparticles of $TiO_2$ or $Al_2O_3$ was experimentally investigated under atmospheric pressure. The results showed that a dispersion of oxide nanoparticles significantly enhances the CHF over that of pure water. Moreover it was found that nanoparticles were seriously deposited on the heater surface during pool boiling of nanofluids. CHF of pure water on a nanoparticle-deposited surface, which is produced during the boiling of nanofluids, was not less than that of nanofluids. The result reveals that the CHF enhancement of nanofluids is absolutely attributed to modification of the heater surface by the nanoparticle deposition. Then, the nanoparticle-deposited surface was characterized with parameters closely related to pool boiling CHF, such as surface roughness, contact angle, and capillary wicking. Finally, reason of the CHF enhancement of nanofluids is discussed based on the changes of the parameters.

• Journal of Periodontal and Implant Science
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• v.42 no.3
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• pp.81-87
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• 2012

Purpose: The characteristics of oxidized titanium (Ti) surfaces varied according to treatment conditions such as duration time and temperature. Thermal oxidation can change Ti surface characteristics, which affect many cellular responses such as cell adhesion, proliferation, and differentiation. Thus, this study was conducted to evaluate the surface characteristics and cell response of thermally treated Ti surfaces. Methods: The samples were divided into 4 groups. Control: machined smooth titanium (Ti-S) was untreated. Group I: Ti-S was treated in a furnace at $300^{\circ}C$ for 30 minutes. Group II: Ti-S was treated at $500^{\circ}C$ for 30 minutes. Group III: Ti-S was treated at $750^{\circ}C$ for 30 minutes. A scanning electron microscope, atomic force microscope, and X-ray diffraction were used to assess surface characteristics and chemical composition. The water contact angle and surface energy were measured to assess physical properties. Results: The titanium dioxide ($TiO_2$) thickness increased as the treatment temperature increased. Additional peaks belonging to rutile $TiO_2$ were only found in group III. The contact angle in group III was significantly lower than any of the other groups. The surface energy significantly increased as the treatment temperature increased, especially in group III. In the 3-(4,5-Dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide assay, after 24 hours of incubation, the assessment of cell viability showed that the optical density of the control had a higher tendency than any other group, but there was no significant difference. However, the alkaline phosphatase activity increased as the temperature increased, especially in group III. Conclusions: Consequently, the surface characteristics and biocompatibility increased as the temperature increased. This indicates that surface modification by thermal treatment could be another useful method for medical and dental implants.

• Journal of the Mineralogical Society of Korea
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• v.28 no.1
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• pp.29-38
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• 2015

Cyanide can be leached out from the cyanidation method which has been used to extract high-purity gold and silver from ores, and it becomes a variety of cyanide complexes associated with heavy metals contained in ores. Such cyanide complexes are considered as persistent and non-degradable pollutants which cause adverse effects on humans and surrounding environments. Based on binding force between heavy metals and cyanide, cyanide complexes can be categorized weak acid dissociable (WAD) and strong acid dissociable (SAD). This study comparatively evaluated the performance of photo-catalytic process with regard to forms of cyanide complexes. In particular, both effects of UV LED wavelength and surface modification of photo-catalyst on the removal efficiency of cyanide complexes were investigated in detail. The results indicate that the performance of photo-catalytic oxidation is significantly affected by the form of cyanide complexes. In addition, the effect of UV LED wavelength on the removal efficiency was quite different between free cyanide and cyanide complexes associated with heavy metals. The results support that the surface modification of photo-catalyst, such as doping can improve overall performance of photo-catalytic oxidation of cyanide complexes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.423-423
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• 2011

Zinc oxide is metal oxide semiconductor with the 3.37 eV bandgap energy. Zinc oxide is very attractive materials for many application fields. Zinc Oxide has many advantages such as high conductivity and good transmittance in visible region. Also it is cheaper than other semiconductor materials such as indium tin oxide (ITO). Therefore, ZnO is alternative material for ITO. ZnO is attracting attention for its application to transparent conductive oxide (TCO) films, surface acoustic wave (SAW), films bulk acoustic resonator (FBAR), piezoelectric materials, gas-sensing, solar cells and photocatalyst. In this study, we synthesized ZnO nanoparticles and defined their physical and chemical properties. Also we studied about the application of ZnO nanoparticles as a photocatalyst and try to find a enhancement photocatalytic activity of ZnO nanorticles.. We synthesized ZnO nanoparticles using spray-pyrolysis method and defined the physical and optical properties of ZnO nanoparticles in experiment I. When the ZnO are exposed to UV light, reduction and oxidation (REDOX) reaction will occur on the ZnO surface and generate O2- and OH radicals. These powerful oxidizing agents are proven to be effective in decomposition of the harmful organic materials and convert them into CO2 and H2O. Therefore, we investigated that the photocatalytic activity was increased through the surface modification of synthesized ZnO nanoparticles. In experiment II, we studied on the stability of ZnO nanoparticles in water. It is well known that ZnO is unstable in water in comparison with TiO2. Zn(OH)2 was formed at the ZnO surface and ZnO become inactive as a photocatalyst when ZnO is present in the solution. Therefore, we prepared synthesized ZnO nanoparticles that were immersed in the water and dried in the oven. After that, we measured photocatalytic activities of prepared samples and find the cause of their photocatalytic activity changes.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.54-54
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• 2010

Zinc oxide is metal oxide semiconductor with the 3.37 eV bandgap energy. Zinc oxide is very attractive materials for many application fields. Zinc Oxide has many advantages such as high conductivity and good transmittance in visible region. Also it is cheaper than other semiconductor materials such as indium tin oxide (ITO). Therefore, ZnO is alternative material for ITO. ZnO is attracting attention for its application to transparent conductive oxide (TCO) films, surface acoustic wave (SAW), films bulk acoustic resonator (FBAR), piezoelectric materials, gas-sensing, solar cells and photocatalyst. In this study, we synthesized ZnO nanoparticles and defined their physical and chemical properties. Also we studied about the application of ZnO nanoparticles as a photocatalyst and try to find a enhancement photocatalytic activity of ZnO nanorticles.. We synthesized ZnO nanoparticles using spray-pyrolysis method and defined the physical and optical properties of ZnO nanoparticles in experiment I. When the ZnO are exposed to UV light, reduction and oxidation(REDOX) reaction will occur on the ZnO surface and generate ${O_2}^-$ and OH radicals. These powerful oxidizing agents are proven to be effective in decomposition of the harmful organic materials and convert them into $CO_2$ and $H_2O$. Therefore, we investigated that the photocatalytic activity was increased through the surface modification of synthesized ZnO nanoparticles. In experiment II, we studied on the stability of ZnO nanoparticles in water. It is well known that ZnO is unstable in water in comparison with $TiO_2$. $Zn(OH)_2$ was formed at the ZnO surface and ZnO become inactive as a photocatalyst when ZnO is present in the solution. Therefore, we prepared synthesized ZnO nanoparticles that were immersed in the water and dried in the oven. After that, we measured photocatalytic activities of prepared samples and find the cause of their photocatalytic activity changes.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.70-70
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• 2013

As the costs of carbon-footprinetd fuels grow continuously and simultaneously atmospheric carbon dioxide concentration increases, solar fuels are receiving growing attention as alternative clean energy carriers. These fuels include molecular hydrogen and hydrogen peroxide produced from water, and hydrocarbons converted from carbon dioxide. For high efficiency solar fuel production, not only light absorbers (oxide semiconductors, Si, inorganic complexes, etc) should absorb most sunlight, but also charge separation and interfacial charge transfers need to occur efficiently. With this in mind, this talk will introduce the fundamentals of solar fuel production and artificial photosynthesis, and then discuss in detail on photoelectrochemical (PEC) water splitting and CO2 conversion. This talk largely divides into two section: PEC water oxidation and PEC CO2 reduction. The former is very important for proton-coupled electron transfer to CO2. For this oxidation, a variety of oxide semiconductors have been tested including TiO2, ZnO, WO3, BiVO4, and Fe2O3. Although they are essentially capable of oxidizing water into molecular oxygen, the efficiency is very low primarily because of high overpotentials and slow kinetics. This challenge has been overcome by coupling with oxygen evolving catalysts (OECs) and/or doping donor elements. In the latter, surface-modified p-Si electrodes are fabricated to absorb visible light and catalyze the CO2 reduction. For modification, metal nanoparticles are electrodeposited on the p-Si and their PEC performance is compared.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.646-651
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• 2018

This paper reports that the electronic properties at a $P3HT/TiO_2$ interface associated with exciton dissociation and transport can be tailored by the insertion of a graphene quantum dot (GQD) layer. For donor/acceptor interface modification in an $ITO/TiO_2/P3HT/Al$ photovoltaic (PV) device, a continuous GQD film was prepared by a sonication treatment in solution that simplifies the conventional processes, including laser fragmentation and hydrothermal treatment, which limits a variety of component layers and involves low cost processing. The high conductivity and favorable energy alignment for exciton dissociation of the GQD layer increased the fill factor and short circuit current. The origin of the improved parameters is discussed in terms of the broad light absorption and enhanced interfacial carrier transport.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.727-730
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• 2004

In this paper, so as to investigate the influence of oxidizer for each metal film using the alumina-based slurry, we have peformed the W/Ti metal-CMP process by adding $H_2O_2$ as a representative oxidizer from 1 wt% to 9 wt%, respectively. As an experimental result, for the case of 5 wt% oxidizer added, the removal rates were improved and polishing selectivity of 1.4 : 1 was obtained. Also, we compared the effects of oxidizer or W-CMP process with three different kind of oxidizers with 5 wt% hydrogen peroxide such as $Fe(NO_3)_3$, $H_2O_2$, and $KIO_3$. Finally, atomic force microscope (AFM) measurements were carried out for the analysis of surface morphology and root mean square (RMS) roughness after CMP Process.