• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.861-866
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• 2010

Tetrapod-shaped ZnO crystals were synthesized through a simple oxidation of metallic Zn powder in air without the presence of any catalysts or substrates. X-ray diffraction data revealed that the ZnO crystals had wurtzite structure. It is supposed that the growth of the tetrapod proceeded in a vapor-solid growth mechanism. As the amount of the source powder increased, the size of the tetrapod decreased. The tip morphology of the tetrapod changed from a needle-like shape to a spherical shape with the oxidation time. ZnO crystals with rod shape were fabricated via the oxidation of Zn and Sn mixture. Sn played an important role in the formation of ZnO crystals with different morphology by affecting the growth mode of ZnO crystals. The cathodoluminescent properties were measured for the samples. The strongest green emission was observed for the rod-shaped ZnO crystals, suggesting that the crystals had the high density of oxygen vacancies.

• Journal of Integrative Natural Science
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• v.2 no.3
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• pp.202-206
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• 2009

Optical images based on the porous silicon exhibiting photoluminescence have been prepared from an electrochemical etching of n-type silicon wafer (boron-doped,<100> orientation, resistivity $1{\sim}10{\Omega}-cm$) by using a beam projector. The images remained in the substrate displayed an optical images correlating to the optical pattern and could be useful for optical data storage. This provides the ability to fabricate complex optical encoding in the surface of silicon.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.690-696
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• 2005

The ultrastructure ore of a nanostructured apatite film nucleated from solution was studied to gain insights into that of bone minerals which is the most important constituent to sustain the strength of bones. Needle-shaped apatite crystal plates with a bimodal size distribution $(\~100\;to\;\~1000 nm)$ were randomly distributed and they were found to grow parallel to the c-axis ([002]), driven by the reduction of surface energy. Between these randomly distributed needle-shaped apatite crystals which are parallel to the film, apatite crystals (20-40nm) with the normal of the grains quasi-perpendicular to the c-axis were observed. These observations suggest that the apatite film is the interwoven structure of apatite crystals with the c-axis parallel and quasi-perpendicular to the fan. In some regions, amorphous calcium phosphate, which is a precursor of apatite, was also observed. In the amorphous phase, small crystalline particle with the size of 2-3 nm were observed. These particles were quite similar, in size and shape, to those observed in the femoral trabecular bone, suggesting the nucleation of apatites by a biomimetic process in vitro is similar to that in vivo.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.127-131
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• 2010

Biomimetic whisker-like apatite was formed on thermally and NaOH-treated titanium powder in a simulated body fluid (SBF). In the early process of the SBF immersion, the surface structure of the titanium powder was loosened, possibly due to the dissolution of $Na^+$ ions on the surface of the titanium powder into SBF. When immersed for 7 days in SBF, fine precipitates appeared on the titanium surfaces; the coating layer (<200 nm in thickness) consisted of nanostructured, amorphous whisker-like and particulate phase, observed by TEM. With the extension of the immersion time to 16 days, the chrysanthemum flower type morphology of carbonated hydroxyapatite with a nanocrystallinity was developed on the surface of the titanium powder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.190-190
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• 2009

Liquid crystals (LCs) which utilize the phase above blue phase temperature range are also known to format the optically nanostructured composites devices based on Kerr effect these days. We report electro-optical characteristics of the polymer-stabilized cholestric LCs by using UV curable monomers at the different temperatures such as blue phase temperature range, blue phase-isotropic transition temperature, and isotropic temperature range. The devices exhibit different electro-optic characteristics.

• Journal of Periodontal and Implant Science
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• v.52 no.4
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• pp.261-281
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• 2022

Purpose: Short implants are a potential alternative to long implants for use with bone augmentation in atrophic jaws. This meta-analysis investigated the survival rate and marginal bone level (MBL) of surface-modified short vs. long implants. Methods: Electronic and manual searches were performed for articles published between January 2010 and June 2021. Twenty-two randomized controlled trials (RCTs) comparing surface-modified short and long implants that reported the survival rate with at least 1 year of follow-up were selected. Two reviewers independently extracted the data, and the risk of bias and quality of evidence were evaluated. A quantitative meta-analysis was performed regarding survival rate and MBL. Results: The failure rates of surface-modified short and long implants differed significantly (risk ratio, 2.28; 95% confidence interval [CI], 1.46, 3.57; P<0.000). Long implants exhibited a higher survival rate than short implants (mean follow-up, 1-10 years). A significant difference was observed in mean MBL (mean difference=-0.43, 95% CI, -0.63, -0.23; P<0.000), favoring the short implants. Regarding the impact of surface treatment in short and long implants, for hydrophilic sandblasted acid-etched (P=0.020) and titanium oxide fluoride-modified (P=0.050) surfaces, the survival rate differed significantly between short and long implants. The MBL differences for novel nanostructured calcium-incorporated, hydrophilic sandblasted acid-etched, and dual acid-etched with nanometer-scale calcium phosphate crystal surfaces (P=0.050, P=0.020, and P<0.000, respectively) differed significantly for short vs. long implants. Conclusions: Short surface-modified implants are a potential alternative to longer implants in atrophic ridges. Long fluoride-modified and hydrophilic sandblasted acid-etched implants have higher survival rates than short implants. Short implants with novel nanostructured calcium-incorporated titanium surfaces, hydrophilic sandblasted acid-etched surfaces, and dual acid-etched surfaces with nanometer-scale calcium phosphate crystals showed less marginal bone loss than longer implants. Due to high heterogeneity, the MBL results should be interpreted cautiously, and better-designed RCTs should be assessed in the future.

• Nuclear Engineering and Technology
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• v.38 no.3
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• pp.201-210
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• 2006

This article presents a brief overview of an important area of neutron scattering: the general principles and techniques of elastic, quasielastic and inelastic scattering from a system composed predominately of incoherent scatterers. The methodology is then applied to the study of water, specifically when it is confined in nanometer-scale environments. The confined water exhibits uniquely anomalous properties in the supercooled state. It also nourishes biological functions, and supports essential chemical reactions in living systems. We focus on recent investigations of water encapsulated in nanoporous silica and carbon nanotubes, hydrated water in proteins and water or hydroxyl species incorporated in nanostructured minerals. Through these scientific examples, we demonstrate the advantages derived from the high sensitivity of incoherent neutron spectroscopy to hydrogen atom motions and hydrogen-bond dynamics, aided by rigorous data interpretation method using molecular dynamics simulations or theoretical modelling. This enables us to probe the inter-/intramolecular vibrations and relaxation/diffusion processes of water molecules in a complex environment.

• Advances in nano research
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• v.10 no.3
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• pp.211-219
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• 2021

The evaluation of the corrosion resistance of titanium with a TiO2 nanotubes top layer was carried out (TiO2 NT). These nanostructures were evolved into anatase nanoparticles without heat treatment in an aqueous medium, which is a novel phenomenon. This work analyzes the layer between the nanotube bottom and the substrate, which is thin and still susceptible to corrosion. The bottom of TiO2 nanotubes having Fluor resulting from the synthesis process changed between amorphous to crystalline anatase with a crystallite size of about 4 nm, which influenced the corrosion rates. Four kinds of samples were evaluated. A) NT by Ti anodizing; B) NTSB for Ti plates, either modifying its surface or anodizing the modified surface; C) NT-480 for anodized Ti and heat-treated (480℃) for reaching the anatase phase; D) NTSB-480 for Ti plates, first, modifying its surface using sandblast, after that, anodizing the modified surface, and finally, heat-treated to 480℃ to compare with samples having induced crystallization and passivation. Four electrochemical techniques were used to evaluate the corrosion rates. The surfaces having TiO2 nanotubes with a sandblast pre-treatment had the highest resistance to corrosion.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.205-211
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• 2022

The Granule Spray in Vacuum (GSV) process is a method of forming a dense nanostructured ceramic coating film by spraying ceramic granules on a substrate at room temperature in a vacuum. In the Granule Spray, the granules made by agglomerating particles with the size from submicrometer to micrometer can be sprayed into the substrate. Once the granules were squashed upon collision with the substrate, they become several dozens of nanometer-sized crystals in vacuum process. The zirconia of the monoclinic phase transform into tetragonal phase at 1150℃. At this time, its volume is changed by about 6.5 %. For this reason, it is widely held that it is difficult to acquire a compact of monoclinic zirconia sinter. In this study, the effect of particle treatment temperature and standoff distance on the substrate of zirconia granules were investigated in GSV. Also, particle treatment temperature, standoff distance, coating efficiency, and microstructure of the film were considered in forming the monoclinic zirconia coating film in GSV without any heating process. The deposited films exhibited monoclinic zirconia phase without any other detectable phase by X-ray diffractometer (XRD).