• Korean Journal of Materials Research
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• v.22 no.4
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• pp.185-189
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• 2012

We report plasma-assisted molecular beam epitaxy of $In_XGa_{1-X}N$ films on c-plane sapphire substrates. Prior to the growth of $In_XGa_{1-X}N$ films, GaN film was grown on the nitride c-plane sapphire substrate by two-dimensional (2D) growth mode. For the growth of GaN, Ga flux of $3.7{\times}10^{-8}$ torr as a beam equivalent pressure (BEP) and a plasma power of 150 W with a nitrogen flow rate of 0.76 sccm were fixed. The growth of 2D GaN growth was confirmed by $in-situ$ reflection high-energy electron diffraction (RHEED) by observing a streaky RHEED pattern with a strong specular spot. InN films showed lower growth rates even with the same growth conditions (same growth temperature, same plasma condition, and same BEP value of III element) than those of GaN films. It was observed that the growth rate of GaN is 1.7 times higher than that of InN, which is probably caused by the higher vapor pressure of In. For the growth of $In_xGa_{1-x}N$ films with different In compositions, total III-element flux (Ga plus In BEPs) was set to $3.7{\times}10^{-8}$ torr, which was the BEP value for the 2D growth of GaN. The In compositions of the $In_xGa_{1-x}N$ films were determined to be 28, 41, 45, and 53% based on the peak position of (0002) reflection in x-ray ${\theta}-2{\theta}$ measurements. The growth of $In_xGa_{1-x}N$ films did not show a streaky RHEED pattern but showed spotty patterns with weak streaky lines. This means that the net sticking coefficients of In and Ga, considered based on the growth rates of GaN and InN, are not the only factor governing the growth mode; another factor such as migration velocity should be considered. The sample with an In composition of 41% showed the lowest full width at half maximum value of 0.20 degree from the x-ray (0002) omega rocking curve measurements and the lowest root mean square roughness value of 0.71 nm.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.77-77
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• 2017

Titanium and its alloys offer attractive properties in a variety of applications. These are widely used for the field of biomedical implants because of its good biocompatibility and high corrosion resistance. Titanium anodizing is often used in the metal finishing of products, especially those can be used in the medical devices with dense oxide surface. Based on SAE/AMS (Society of Automotive Engineers/Aerospace Material Specification) 2488D, it has the specification for industrial titanium anodizing that have three different types of titanium anodization as following: Type I is used as a coating for elevated temperature forming; Type II is used as an anti-galling coating without additional lubrication or as a pre-treatment for improving adherence of film lubricants; Type III is used as a treatment to produce a spectrum of surface colours on titanium. In this study, we have focused on Type II anodization for the medical (dental and orthopedic) application, the anodized surface was modified with gray color under alkaline electrolyte. The surface characteristics were analyzed with Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM), surface roughness, Vickers hardness, three point bending test, biocompatibility, and corrosion (potentiodynamic) test. The Ti-6Al-4V alloy was used for specimen, the anodizing procedure was conducted in alkaline solution (NaOH based, pH>13). Applied voltage was range between 20 V to 40 V until the ampere to be zero. As results, the surface characteristics of anodic oxide layer were analyzed with SEM, the dissecting layer was fabricated with FIB method prior to analyze surface. The surface roughness was measured by arithmetic mean deviation of the roughness profile (Ra). The Vickers hardness was obtained with Vickers hardness tester, indentation was repeated for 5 times on each sample, and the three point bending property was verified by yield load values. In order to determine the corrosion resistance for the corrosion rate, the potentiodynamic test was performed for each specimen. The biological safety assessment was analyzed by cytotoxic and pyrogen test. Through FIB feature of anodic surfaces, the thickness of oxide layer was 1.1 um. The surface roughness, Vickers hardness, bending yield, and corrosion resistance of the anodized specimen were shown higher value than those of non-treated specimen. Also we could verify that there was no significant issues from cytotoxicity and pyrogen test.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.705-710
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• 2015

The fabrication process of thin boron-doped nanocrystalline diamond (B-NCD) microelectrodes on fused silica single mode optical fiber cladding has been investigated. The B-NCD films were deposited on the fibers using Microwave Plasma Assisted Chemical Vapor Deposition (MW PA CVD) at glass substrate temperature of 475 ℃. We have obtained homogenous, continuous and polycrystalline surface morphology with high sp³ content in B-NCD films and mean grain size in the range of 100-250 nm. The films deposited on the glass reference samples exhibit high refractive index (n=2.05 at λ=550 nm) and low extinction coefficient. Furthermore, cyclic voltammograms (CV) were recorded to determine the electrochemical window and reaction reversibility at the B-NCD fiber-based electrode. CV measurements in aqueous media consisting of 5 mM K₃[Fe(CN)₆] in 0.5 M Na₂SO₄ demonstrated a width of the electrochemical window up to 1.03 V and relatively fast kinetics expressed by a redox peak splitting below 500 mV. Moreover, thanks to high-n B-NCD overlay, the coated fibers can be also used for enhancing the sensitivity of long-period gratings (LPGs) induced in the fiber. The LPG is capable of measuring variations in refractive index of the surrounding liquid by tracing the shift in resonance appearing in the transmitted spectrum. Possible combined CV and LPG-based measurements are discussed in this work.

• Korean Journal of Medicinal Crop Science
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• v.27 no.4
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• pp.284-291
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• 2019

Background: Ginseng root rot disease, caused by Cylindrocarpon destructans and Fusarium solani is a major cause of replant failure in continuous cropping ginseng. Methods and Results: To control replant injury in soil infected with C. destructans and F. solani, biosolarization was performed by covering the plot with transparent polyethylene film after adding green manure of maize and sunflower for the summer season. Per 10 a, fresh and dry weight of maize was 10.1 and 2.5 tons, respectively, and that of sunflower was 8.1 tons and 1.2 tons, respectively. Mean maximum temperature at 20 cm depth was $33.2^{\circ}C$, $41.5^{\circ}C$ and $41.8^{\circ}C$ in the control, maize-incorporated and sunflower-incorporated plots, respectively. The elapsed time over $40^{\circ}C$ was 36.4 h in the maize-incorporated plot and 77.3 h in the sunflower-incorporated plot. Biosolarization increased $NO_3$ content in soil, while content of organic matter, Ca, and Mg was decreased. Electrical conductivity, $NO_3$ and $P_2O_5$ in soil significantly increased after two years of biosolarization. The number of spores of C. destructans in soil was significantly decreased by biosolarization, and sunflower treatment was more effective than maize treatment in decreasing the number of spores. Root yield of 3-year-old ginseng was significantly increased by biosolarization, however, there was no significant difference between maize and sunflower treatments. Rate of root rot in 3-year-old ginseng decreased to 16.5% with the incorporation maize and 5.0% with the incorporation of sunflower, while that in control 25.6%. Conclusions: Biosolarization was effective in inhibiting ginseng root rot by decreasing the density of root rot disease and improving soil chemical properties.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.1
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• pp.66-78
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• 2004

The objective of this study was to apply the vibration technique to reduce the viscosity of bonding adhesives and thereby compare the bond strength and resin penetration in enamel and dentin achieved with those gained using the conventional technique and vibration technique. For enamel specimens, thirty teeth were sectioned mesio-distally. Sectioned two parts were assigned to same adhesive system but different treatment(vibration vs. non-vibration). Each specimen was embedded in 1-inch inner diameter PVC pipe with a acrylic resin. The buccal and lingual surfaces were placed so that the tooth and the embedding medium were at the same level. The samples were subsequently polished silicon carbide abrasive papers. Each adhesive system was applied according to its manufacture's instruction. Vibration groups were additionally vibrated for 15 seconds before curing. For dentin specimen, except removing the coronal part and placing occlusal surface at the mold level, the remaining procedures were same as enamel specimen. Resin composite(Z250. 3M. U.S.A.) was condensed on to the prepared surface in two increments using a mold kit(Ultradent Inc., U.S.A.). Each increments was light cured for 40 seconds. After 24 hours in tap water at room temperature, the specimens were thermocycled for 1000cycles. Shear bond strengths were measured with a universal testing machine(Instron 4465, England). To investigate infiltration patterns of adhesive materials, the surface of specimens was examined with scanning electron microscope. The results were as follows: 1. In enamel the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration group(group 1, 3, 5). The differences were statistically significant except AQ bond group. 2. In dentin, the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration groups(group 1, 3, 5). But the differences were not statistically significant except One-Up Bond F group. 3. The vibration group showed more mineral loss in enamel and longer resin tag and greater number of lateral branches in dentin under SEM examination.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.37 no.2
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• pp.149-154
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• 1992

Buckwheat has been a popular favorite food crop in Korea for a long time. The objective of the study was to investigate the effects of climatic conditions and cultural methods on grain yields of summer buckwheat variety Sinnong 1 planted during the spring season in Suwon, Korea from 1989 to 1991. Frost minimum temperature of late April was -0.3$^{\circ}C$ in 1990 being very low as compared with 3.7$^{\circ}C$ of the normal year, and affected early growth of the seedlings emerging from the soil surface. In late May of 1990, the frost minimum temperature was 7.3$^{\circ}C$ being low as compared with 8.8$^{\circ}C$ of the normal year, and also induced cold injury to fertilization and grain filling. Total precipitation 374.5mm of mid and late June, 1990 provided serious damage to the grain filling and maturing buckwheat seeds and along with causing seed sprouting before harvest. However, the climates of 1989 and 1991 were very good for the growth and development of spring-sown buckwheats. When summer buckwheat cultivar Sinnong 1 was planted on April 20, 1989, its highest grain yields 268-292kg /10a were harvested from the plots of seeding rate 8kg /10a, drill seeding and polyethylene film mulching, and the mean grain yield of the plots was 238kg /10a in 1989, but 64.3kg in Suwon, and 40.2kg /10a in Muan in 1990. In 1991 maximum grain yield 277kg /10a was produced from the April 15 planted and vinyl-mulched plot, and 255kg /10a from the April 25 planted and non-mulched plot. Herbicide Alachlor-sprayed plots produced lower grain yields than no weed control and manual weeding plots. Mechanized drill-seeding saved 83～84% in planting hours as compared with manual broadcasting 21.6 hours /ha, and produced 9% more in grain yields from the two-season croppings of mechanized drill-seeding culture being 364kg /10a in total yields per year.