• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.198.1-198.1
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• 2014

Many efforts have been devoted on chemical modification of graphene layer to modulate its electrical properties. In the previous report, laser irradiation on the CYTOP(perfluoropolymer) doped graphene layer induces chemical modification of it, resulting in the insulating I-V characteristics. While the results strongly denoted C-F bond formation after irradiation, the detailed process of photo-induced chemical change is not known yet. To probe this, we utilized synchrotron based SPEM (scanning photoelectron emission spectroscopy) in NSRRC, Taiwan. We irradiate the sample by photon of 614 eV in a stepwise manner as a function of time. As photon irradiation increased, difluoride moieties in the CYTOP was broken, and then formed mono-fluoride with carbon atoms consisting graphene layer.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.792-799
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• 2019

The present study aims to investigate the fluorination of thorium oxide ($ThO_2$) by ammonium hydrogen difluoride ($NH_4HF_2$). Fluorination was performed at room temperature by mixing $ThO_2$ and $NH_4HF_2$ at different molar ratios, which was then left to react for 20 days. Next, the mixtures were analyzed using X-ray diffraction (XRD) at the intervals of 5, 10, 15, and 20 days, followed by the heating of the mixtures at $450-750^{\circ}C$ with argon gas flow. The characterization of $ThF_4$ was established using X-ray diffraction (XRD) and scanning electron microscopy-dispersion X-ray spectroscopy (SEM-EDX). In this study, ammonium thorium fluoride was synthesized through the fluorination of $ThO_2$ at room temperature. The optimum molar ratio in synthesizing ammonium thorium fluoride was 1.0:5.5 ($ThO_2:NH_4HF_2$) with 5 days reaction time. In addition, the heating of ammonium thorium fluoride at $450^{\circ}C$ was sufficient to produce $ThF_4$. Overall, this study proved that $NH_4HF_2$ is one of the fluorination agents that is capable of synthesizing $ThF_4$.

• Membrane Journal
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• v.23 no.3
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• pp.204-210
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• 2013

Recently, many applications with grapheneoxide (GO) have been reported. But GO membrane for water treatment has not been developed. In this study we prepared polyvinylidene difluoride (PVdF) nanofiber/GO hybrid membrane (FG) for the microfiltration application. The PVdF substrate membrane was prepared by using the electrospinning method with a solution of PVdF in N,N-dimethylacetamide (DMAc) and acetone. GO sheets used in this study were prepared by modified Hummer's method. The PVdF/GO hybrid membrane was finally prepared by spraying the GO solution dispersed in ethanol on the PVdF nanofiber. The successfully prepared FG was thoroughly examined by SEM, Raman, contact angle, porometer and UTM, and water-flux was measured with designed cell (Dead-End Cell). From the contact angle results, it was found that the surface of FG membrane was reformed by hydrophilic property and the water permeability was increased about 2.5 times than that of the nascent PVdF membrane, indicating the possible alternative of the commercial MF membrane.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.441-451
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• 2023

Ultrasound transducers are an essential component of combined photoacoustic and ultrasound imaging systems and play an important role in image evaluation. However, ultrasound transducers are opaque; therefore, light must bypass the ultrasound transducer to reach the target point to produce a photoacoustic image. Providing different paths for the optical and acoustic signals results in a complicated system design, increasing the system volume. To overcome these problems, an optically Transparent Ultrasound Transducer (TUT) was developed. Unlike conventional opaque ultrasound transducers, optically TUT can be fabricated by a variety of manufacturing methods and they are suitable for use with specific piezoelectric elements and serve various purposes. In this study, a comparative analysis of the results of using Lithium Niobate (LNO), Lead Magnesium Niobate-Lead Titanate (PMN-PT), and Polyvinylidene Difluoride (PVDF), which are materials used in piezoelectric element-based TUT. LNO is a piezoelectric element widely used in TUT, and PMN-PT has been actively studied recently with a higher transmission and reception rate than LNO. Existing TUT have lower ultrasound resolution than photoacoustic resolution, but they have recently been manufacturing focused TUT with high ultrasound resolution using PVDF. A comparative analysis of the production results of these TUT was performed.

• Journal of the Korean Chemical Society
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• v.60 no.1
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• pp.21-27
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• 2016

Novel push-pull chromophores containing 5’-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)aniline (bisDMFA) as a donor and phenylazo-methylpyrrolyl-boron difluoride (PhAPy-BF₂) as an acceptor were designed and synthesized by the Knoevenagel condensation reaction for organic solar cells. Various electron withdrawing moieties were effectively introduced using 2,4-dimethyl-1H-pyrrole to afford new asymmetric BF₂-azopyrrole molecules that were characterized by UV-vis spectroscopy and cyclic voltammetry measurements.

• Membrane Journal
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• v.15 no.1
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• pp.22-33
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• 2005

Asymmetric PVDF membranes were prepared by the phase inversion from casting solutions containing PVDF, NMP as solvent and 1,4-dioxane, DGDE, acetone, or GBL as additives by immersing them in water. The effects of various additives on the casting solution properties, permeation properties, and membrane structures were investigated. Low miscibility of 1,4-dioxane, DGDE and acetone with the coagulant (water) compared with NMP resulted in reducing the membrane pore size. When DGDE is used as an additive, the pore size was reduced because of its incipient sharp interface formation in the water. GBL increased membrane pore size because of its polarity compared to that of NMP. The PVDF membranes with various pore sizes could be obtained by controlling the amount of additive. The effect of mixed solvent (aqueous and non-aqueous solution) on permeation through membrane was investigated. Not only solution viscosity but surface tension affected solvent permeation.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.1
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• pp.116-122
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• 2007

A 2-step process for the safe disposal of chemical warfare agents(agent hydrolysis followed by incineration In the submerged-quench incinerator) was studied to obtain basic data for the design of pilot plant in the future. Sample materials used for the hydrolysis reaction were sarin(GB), sulfur mustard (HD), and methylphosphonic difluoride(DF). The hydrolysates of these materials were thermally destroyed in a submerged-quench incineration system. Experimental conditions for achieving destruction efficiency of 99.99% in both steps were established and phosphoric acid was recovered from the waste water when destroying DF hydrolysate in the incinerator. Treated water could be reused as process water for the agent hydrolysis.

• YAKHAK HOEJI
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• v.34 no.1
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• pp.11-14
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• 1990

$NH_2-terminal$ amino acid sequence analysis of monoclonal antibody is very important to identify gene family and diversities of antigen-antibody recognition. When we used the PVDF (Polyvinylidene difluoride) membrane blotting method, we could easily analyze $NH_2-terminal$ sequence of monoclonal-antibody which specifically binds to phosphatidylinositol 4,5-biphosphate. PVDF membrane is an ideal solid-phase support for sequence analysis, especially when used with electroblotting method. This method is superior to continual method and will be applied to the sequence analysis of picomole quantities of proteins by gel electrophoresis.

• Applied Microscopy
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• v.45 no.4
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• pp.195-198
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• 2015

Gas-assisted etching (GAE) with focused ion beam (FIB) was applied to prepare plan-view specimens of Cu thin-layer on a silicon substrate for transmission electron microscopy (TEM). GAE using $XeF_2$ gas selectively etched the silicon substrate without volume loss of the Cu thin-layer. The plan-view specimen of the Cu thin film prepared by FIB milling with GAE was observed by scanning electron microscopy and $C_S$-corrected high-resolution TEM to estimate the size and microstructure of the TEM specimen. The GAE with FIB technique overcame various artifacts of conventional FIB milling technique such as bending, shrinking and non-uniform thickness of the TEM specimens. The Cu thin film was uniform in thickness and relatively larger in size despite of the thickness of <200 nm.

• Journal of ILASS-Korea
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• v.8 no.1
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• pp.16-22
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• 2003

Zeta potential measurements of colloid particles suspended in a liquid are performed by a Zeta Meter developed. There are many applications of colloid stability in spray technology, paints, wastewater treatment, and pharmaceuticalse. Zeta potentials of charged particles are obtained by measuring the electrophoretic velocities of the particles using video enhanced microscopy and image analysis program. The values of zeta potential of polystyrene latex(PSL), $silica(SiO_2)$M, polyvinylidence difluoride(PVDF), silicon nitride, and alumina particles in deionized (DI) water were measured to be -40.5, -31.9, -25.2, -15.1 and -10.1mV, respectively. The particles having high zeta potential less than -20 mV are stable in DI water, because the double layers of them have strong repulsive forces mutually, and the particles having low zeta potential over -20mV are unstable due to Van Der Waals forces. Silica(>20nm), PSL, aluminum and PVDF particles were found to be stable that would remain separate and well disperse, while silicon nitride and alumina particles were found to be unstable that would gradually agglomerate in DI water.