• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.2
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• pp.85-90
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• 2003

In this work $Cd_{4}GeSe_{6}$ and $Cd_{4}GeSe_{6}$ : $Co^{2+}$ single crystals were grown by the chemical transport reaction method and the structure of $Cd_{4}GeSe_{6}$ and $Cd_{4}GeSe_{6}$ : $Co^{2+}$ single crystals were monoclinic structure. The temperature dependence of optical energy 9ap was fitted well to Varshni equation. Also, the entropy, enthalpy and heat capacity were deduced from the temperature dependence of optical energy gap.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.125-129
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• 2016

In this study, we have investigated a high-temperature AlN nucleation layer and AlGaN epilayers on c-plane sapphire substrate by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscope (SEM) and Raman scattering measurements have been exploited to study the crystal quality, surface morphology, and residual strain of the HT-AlN nucleation layer. These analyses reveal that the insertion of an LT-AlN nucleation layer can improve the crystal quality, smooth the surface morphology of the HT-AlN nucleation layer and further reduce the threading dislocation density of AlGaN epifilms. The mechanism of inserting an LT-AlN nucleation layer to enhance the optical properties of HT-AlN nucleation layer and AlGaN epifilm are discussed from the viewpoint of driving force of reaction in this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.320-320
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• 2007

Nowadays, ZnO thin films are investigated as transparent conductive electrodes for use in optoelectronics devices including flat displays, thin films transistors, solar cells because of their unique optical and electrical properties. For the use as transparent conductive electrodes, a film has to have low resistivity, high absorption in the ultra violent light region and high optical transmission in the visible region. Different technologies such as electron beam evaporation, chemical vapor deposition, laser evaporation, DC and RF magnetron sputtering and have been reported to produce thin films of ZnO with adequate performance for applications. However, highly transparent and conductive doped-ZnO thin films deposited by a metal-organic decomposition method have not been reported before. In this work, the effect of dopant concentration, heating treatment and annealing in areducing atmosphere on the structure, morphology, electrical and optical properties of ZnO thin films deposited on glass substrates by a Sol-gel method are investigated.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.189-193
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• 2012

ZnO nanorods were grown on the $Cd_xZn_{1-x}O$ seed layers with various Cd mole fractions by hydrothermal method. The effects of the Cd mole fraction for $Cd_xZn_{1-x}O$ seed layers on the structural and optical properties of the ZnO nanorods were investigated by scanning electron microscopy, X-ray diffraction, and photoluminescence. The narrowest full-width at half-maximum and largest grain size of the $Cd_xZn_{1-x}O$ seed layers, indicating improvement in crystal quality, were observed at the Cd mole fraction of 0.5. At the Cd mole fraction of 0.5, the largest enhancement in the density, the crystal quality, and the growth rate of the ZnO nanorods was observed while their appearance was not affected significantly by the incorporation of the Cd in the $Cd_xZn_{1-x}O$ seed layers. Consequently, the luminescent properties of the ZnO nanorods were enhanced. The largest improvement in the structural and optical properties of the ZnO nanorods was observed at the Cd mole fraction of 0.5.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.884-890
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• 2002

An inorganic-organic hybrid system, silica-poly(ethylene glycol) songel is reported. This system was prepared via sol-gel method by varying varous processing variables. e.g. ultrasonic radiation time, gelling temperanture, PEG content and its molecular weight. Various experimental techniques wee employed to analyze the morphological, mechanical and optical properties of the system. The results were discussed in the light of existing theories. The sonogel system exhibited the common features of inorganic-organic hybrids. $SiO_2-10$ wt% PEG sonogel exhibited the morphological and optical properties superior to those reported earlier for the classic gels and found suitable for device applications.

• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.620-624
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• 2004

Optical emission studies were performed to investigate thermal and dynamical properties of a plume produced by laser ablation of a graphite target in a nitrogen atmosphere. Experimental spectra of $C_2(d^3{\Pi}_g{\to}a^3{\Pi}_u$, ${\Delta}_V$=1) and CN ($B^2{\Sigma}^+{\to}X^2{\Sigma}^+,{\Delta}_V=0)$ were simulated to obtain the vibrational and rotational temperatures of the electronically excited species at various laser fluences and distances from the target. The spectroscopic temperatures of both molecules were found to be nearly independent of the laser fluence. The temperature of CN molecules was peaked in the middle of the plume while that of $C_2$decreased with increase in the distance. At a given distance, the temperature of CN molecules was clearly higher than that of $C_2$.

• Journal of Powder Materials
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• v.28 no.5
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• pp.429-434
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• 2021

Magnetic nanoparticles have a significant impact on the development of basic sciences and nanomedical, electronic, optical, and biotech industries. The development of magnetic structures with size homogeneity, magnetization, and particle dispersibility due to high-quality process development can broaden their utilization for separation analysis, structural color optics using surface modification, and energy/catalysts. In addition, magnetic nanoparticles simultaneously exhibit two properties: magnetic and plasmon resonance, which can be self-assembled and can improve signal sensitivity through plasmon resonance. This paper reports typical examples of the synthesis and properties of various magnetic nanoparticles, especially magnetoplasmonic nanoparticles developed in our laboratory over the past decade, and their optical, electrochemical, energy/catalytic, and bio-applications. In addition, the future value of magnetoplasmonic nanoparticles can be reevaluated by comparing them with that reported in the literature.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.48-48
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• 2011

We have developed a chemically-driven top-down approach using vapor phase HCl to form various GaN nanostructures and successfully demonstrated dislocation-free and strain-relaxed GaN nanostructures without etching damage formed by a selective dissociation method. Our approach overcomes many limitations encountered in previous approaches. There is no need to make a pattern, complicated process, and expensive equipment, but it produces a high-quality nanostructure over a large area at low cost. As far as we know, this is the first time that various types of high-quality GaN nanostructures, such as dot, cone, and rod, could be formed by a chemical method without the use of a mask or pattern, especially on the Ga-polar GaN. It is well known that the Ga-polar GaN is difficult to etch by the common chemical wet etching method because of the chemical stability of GaN. Our chemically driven GaN nanostructures show excellent structure and optical properties. The formed nanostructure had various facets depending on the etching conditions and showed a high crystal quality due to the removal of defects, such as dislocations. These structure properties derived excellent optical performance of the GaN nanostructure. The GaN nanostructure had increased internal and external quantum efficiency due to increased light extraction, reduced strain, and improved crystal quality. The chemically driven GaN nanostructure shows promise in applications such as efficient light-emitting diodes, field emitters, and sensors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.102-102
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• 2008

Sapphire (${\alpha}-Al_2O_3$) has been used as the substrate of opto-electronic device because of characteristics of thermal stability, comparatively low cost, large diameter, optical transparency and chemical compatibility. However, there is difficulty in the etching and patterning due to the physical stability of sapphire and the selectivity with sapphire and mask materials [1,2]. Therefore, sapphire has been studied on the various fields and need to be studied, continuously. In this study, the etching properties of sapphire substrate were investigated with various $CH_4$/Ar gas combination, radio frequency (RF) power, DC-bias voltage and process pressure. The characteristics of the plasma were estimated for mechanism using optical emission spectroscopy (OES). The chemical compounds on the surface of sapphire substrate were investigated using energy dispersive X-ray (EDX). The chemical reaction on the surface of the etched sapphire substrate was observed by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was used to investigate the vertical and slope profiles.

• Current Photovoltaic Research
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• v.1 no.2
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• pp.97-102
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• 2013

Aluminum-doped zinc oxide (AZO) thin films were prepared by dc magnetron sputtering at room temperature and the effect of heat treatment on the structural, electrical and optical properties of the films were examined. As the annealing temperature and time increased, the resistivity decreased and the transmittance improved. All AZO films had c-axis oriented (002) plane of ZnO, regardless of the annealing process employed. As the annealing temperature and time increased, the crystallinity of AZO thin films increased due to the formation of a new ZnO phase in which Al was substituted for Zn. However, at the high annealing temperature of $400^{\circ}C$, the resistivity of the films increased via separation of Zn and Al from ZnO phase due to their low melting points. X-ray diffraction, field emission scanning electron micrograph and Hall effect measurement confirmed the formation of uniformly distributed new grains of ZnO substituted with Al. The variation of Al contents in AZO films was shown to be the primary factor for the changes in resistivity and carrier concentration of the films.