• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.281-284
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• 2004

Optical imaging and spectroscopy of G353.2+0.9, the brightest part of the giant H II region NGC 6357, shows that this H II region is optically thin, contains ${\~}300\;M_{\bigodot}$ of ionized gas and is probably expanding into the surrounding medium. Its chemical composition is similar to that found in other H II regions at similar galactocentric distances if temperature fluctuations are significant. The inner regions are probably made of thin shells and filaments, whereas extended slabs of material, maybe shells seen edge-on, are found in the periphery. The radio continuum and H$\alpha$ emission maps are very similar, indicating that most of the optical nebula is not embedded in the denser regions traced by molecular gas and the presence of IR sources. About $10^{50}$ UV photons per second are required to produce the H$\beta$ flux from the 1l.3'${\times}$10' region surrounding the Pis 24 cluster that is south of G353.2+0.9. Most of the energy powering this region is produced by the 03-7 stars in Pis 24. Most of the 2MASS sources in the field with large infrared excesses are within G353.2+0.9, indicating that the most recent star forming process occured within it. The formation of Pis 24 preceded and caused the formation of this new generation of stars and may be responsible for the present-day morphology of the entire NGC 6357 region.

• Korean Journal of Materials Research
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• v.23 no.11
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• pp.655-660
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• 2013

Photoelectrochemical cells have been used in photolysis of water to generate hydrogen as a clean energy source. A high efficiency electrode for photoelectrochemical cell systems was realized using a ZnO hierarchical nanostructure. A ZnO nanofiber mat structure was fabricated by electrospinning of Zn solution on the substrate, followed by oxidation; on this substrate, hydrothermal synthesis of ZnO nanorods on the ZnO nanofibers was carried out to form a ZnO hierarchical structure. The thickness of the nanofiber mat and the thermal annealing temperature were determined as the parameters for optimization. The morphology of the structures was examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The performance of the ZnO nanofiber mat and the potential of the ZnO hierarchical structures as photoelectrochemical cell electrodes were evaluated by measurement of the photoelectron conversion efficiencies under UV light. The highest photoconversion efficiency observed was 63 % with a ZnO hierarchical structure annealed at $400^{\circ}C$ in air. The morphology and the crystalline quality of the electrode materials greatly influenced the electrode performance. Therefore, the combination of the two fabrication methods, electrospinning and hydrothermal synthesis, was successfully applied to fabricate a high performance photoelectrochemical cell electrode.

• Bulletin of the Korean Chemical Society
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• v.29 no.4
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• pp.817-821
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• 2008

We have investigated the influence of the crystal structure on the chemical bonding nature and photocatalytic activity of cubic and hexagonal perovskite A[$Cr_{1/2}Ta_{1/2}$]O3 (A = Sr, Ba) compounds. According to neutron diffraction and field emission-scanning electron microscopy, the crystal structure and particle size of these compounds are strongly dependent on the nature of A-site cations. Also, it was found that the face-shared octahedra in the hexagonal phase are exclusively occupied by chromium ions, suggesting the presence of metallic (Cr-Cr) bonds. X-ray absorption and diffuse UV-vis spectroscopic analyses clearly demonstrated that, in comparison with cubic Sr[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase, hexagonal Ba[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase shows a decrease of Cr oxidation state as well as remarkable changes in interband Cr d-d transitions, which can be interpreted as a result of metallic (Cr-Cr) interactions. According to the test of photocatalytic activity, the present semiconducting materials have a distinct activity against the photodegradation of 4-chlorophenol. Also the Srbased compound was found to show a higher photocatalytic activity than the Ba-based one, which is attributable to its smaller particle size and its stronger absorption in visible light region.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3335-3339
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• 2013

Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons ($D^{\circ}X$), and the first LO phonon replicas of $D^{\circ}X$, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni's empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.111.1-111.1
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• 2012

Interest in flexible transparent conducting films (TCFs) has been growing recently mainly due to the demand for electrodes incorporated in flexible or wearable displays in the future. Indium tin oxide (ITO) thin films, which have been traditionally used as the TCFs, have a serious obstacle in TCFs applications. SWNTs are the most appropriate materials for conductive films for displays due to their excellent high mechanical strength and electrical conductivity. In this work, the fabrication by the spraying process of transparent SWNT films and reduction of its sheet resistance on PET substrates is researched Arc-discharge SWNTs were dispersed in deionized water by adding sodium dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWNT was spray-coated on PET substrate and dried on a hotplate. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then was doped with Au-ionic doping treatment, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. This was confirmed and discussed on the XPS and UPS studies. We show that 87 ${\Omega}/{\Box}$ sheet resistances with 81% transmittance at the wavelength of 550nm. The changes in electrical and optical conductivity of SWNT film before and after Au-ionic doping treatments were discussed. The effect of Au-ion treatment on the electronic structure change of SWNT films was investigated by Raman and XPS.

• Journal of the Korean Chemical Society
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• v.51 no.6
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• pp.513-519
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• 2007

A vesicle forming polymer, poly(sodium acrylamidoundecanoate) (PSAU) and a water-soluble distyrylbenzene- based fluorophore, TPADSB-C were synthesized and characterized by using UV-vis and photoluminescence (PL) spectroscopy. An inter-chain vesicle formation of PSAU was observed at ~0.01 g/L from N-phenyl naphthylamine fluorescence measurement with changing PSAU concentration in water. Above critical aggregation concentration of PSAU, optical properties of TPADSB-C were investigated to study the microenvironment modulation through dye incorporation in the polymeric vesicle. The emission of TPADSB-C in the presence of PSAU vesicles was blue-shifted and the PL quantum efficiency was increased to 90% due to the microenvironment (e.g. polarity) change in aqueous solution. This study shows that the polymeric vesicle containing molecular fluorophores has a great potential as an efficient, stable and biocompatible labeling tag in biological cell imaging.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1181-1187
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• 2013

Water-dispersible ZnS:Mn nanocrystals were synthesized by capping the surface of the nanocrystal with O-(2-Aminoethyl)polyethylene glycol (PEG-$NH_2$, Mw = 10,000 g/mol) and O-(2-Carboxyethyl)polyethylene glycol (PEG-COOH, Mw = 10,000 g/mol) molecules. The modified PEG capped ZnS:Mn nanocrystal powders were thoroughly characterized by XRD, HR-TEM, EDXS, ICP-AES and FT-IR spectroscopy. The optical properties were also measured by UV/Vis and photoluminescence (PL) spectroscopies. The PL spectra showed broad emission peaks at 600 nm with similar PL efficiencies of 7.68% (ZnS:Mn-PEG-NH2) and 9.18% (ZnS:Mn-PEG-COOH) respectively. The measured average particle sizes for the modified PEG capped ZnS:Mn nanocrystals by HR-TEM images were 5.6 nm (ZnS:Mn-PEG-NH2) and 6.4 nm (ZnS:Mn-PEG-COOH), which were also supported by Debye-Scherrer calculations. In addition, biological toxicity effects of the nanocrystals over the growth of wild type E. coli were investigated. They showed no biological toxicity to E. coli until very high concentration dosage of 1 mg/mL of the both nanocrystal samples.

• Korean Journal of Materials Research
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• v.24 no.3
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• pp.145-151
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• 2014

Solution-based Sb-doped $SnO_2$ (ATO) transparent conductive oxides using a low-temperature process were fabricated by an electrospray technique followed by spin coating. We demonstrated their structural, chemical, morphological, electrical, and optical properties by means of X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy, Hall effect measurement system, and UV-Vis spectrophotometry. In order to investigate optimum electrical and optical properties at low-temperature annealing, we systemically coated two layer, four layer, and six layers of ATO sol-solution using spin-coating on the electrosprayed ATO thin films. The resistivity and optical transmittance of the ATO thin films decreased as the thickness of ATO sol-layer increased. Then, the ATO thin films with two sol-layers exhibited superb figure of merit compared to the other samples. The performance improvement in a low temperature process ($300^{\circ}C$) can be explained by the effect of enhanced carrier concentration due to the improved densification of the ATO thin films causing the optimum sol-layer coating. Therefore, the solution-based ATO thin films prepared at $300^{\circ}C$C exhibited the superb electrical (${\sim}7.25{\times}10^{-3}{\Omega}{\cdot}cm$) and optical transmittance (~83.1 %) performances.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.10
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• pp.888-893
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• 2016

In this study, the solution plasma process was utilized with the aim of degrading synthetic dyes in water at atmospheric pressure. The experiments were conducted in a batch-type reactor consisting of a symmetric wire-wire electrode configuration with rhodamine B (RhB) as the target synthetic dye. The effects of the plasma treatment time and initial dye concentration on the RhB degradation were investigated by monitoring the change in absorbance of RhB solutions. The RhB solutions turned lighter in color and finally colorless with prolonged plasma treatment time, indicating the destruction of dye molecules. The RhB solutions were found to have degraded, following the first-order kinetic process. However, for high initial RhB concentrations, another kinetic process or factor seems to play a dominant role at the initial degradation stage. The fitted first-order rate constant decreased as the initial concentration increased. This result suggests that the degradation behavior and kinetic process of the RhB solution strongly depends on its initial concentration. The RhB degradation is considered to be due to a combination of factors, including the formation of chemically oxidative species, as well as the emission of intense UV radiation and high-energy electrons from the plasma. We believe that the solution plasma process may prove to be an effective and environment-friendly method for the degradation or remediation of synthetic dye in wastewater.

• Journal of the Korean Association of Geographic Information Studies
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• v.14 no.2
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• pp.109-127
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• 2011

Atmospheric aerosols, small particles in the atmosphere, are one of the important parameters in climate change and human health. Additionally, accurate estimates of aerosol species are increasingly important in environmental impact assessment studies. Recent advances in global satellite remote sensing provide powerful tool for air quality monitoring. This study explores the potential usage of satellite derived data such as atmospheric aerosols for air quality monitoring as well as climate change study. The objectives of this study is to understand the general features of the global distribution of type dependent aerosols. A detailed spatio-temporal variability of the each different satellite dataset shows the variation of the global zonal average and specific geographical regions where the strong emission sources are located. Especially, significantly large aerosol amounts are observed in Asia and Africa because of the desert dust storm, anthropogenic and biomass burning emissions.