• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.202.1-202.1
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• 2013

ZnO nanostructure was fabricated on a Si substrate using two-step growth. The seed layer was grown on the Si substrate by a sol-gel spin-coating. In the first step, ZnO nanorods were grown by a hydrothermal method at $140^{\circ}C$ for 5 min. In the second step, a ZnO thin film was grown on the ZnO nanorods by spin-coating. After growth, these films were annealed at $800^{\circ}C$ for 10 min. Electrical and optical properties of ZnO nanostructures have modified by plasma-assisted molecular beam epitaxy (PA-MBE) regrowth. The carrier concentration and resistivity increased by PA-MBE regrowth. In the photoluminescence, the full width at half maximum and intensity were decreased and increased, respectively, by PA-MBE regrowth.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.183-186
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• 2006

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si AR layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layer were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The surface morphology of porous Si layers were investigated using SEM. The formation of a porous Si layer about $0.1{\mu}m$ thick on the textured silicon wafer result in an effective reflectance coefficient $R_{eff}$ lower than 5% in the wavelength region from 400 to 1000nm. Such a surface modification allows improving the Si solar cell characteristics.

• Fire Science and Engineering
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• v.23 no.3
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• pp.17-22
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• 2009

Epoxy powder is being in use for insulation materials widely. Especially, in cause of coating insulation can be caused electrical fire and explosion by Joul's heat. This study has been compared and examined around breakdown, arc discharge, and V-t about insulation of Epoxy powder. Also, it has been researched about insulation which is cause of electrical fire and its basic data. According to temperature change, sample KS was stable before the Tg to be about $8{\sim}10%$ decrease in the breakdown test. In case of V-t and arc discharge, it had been kept up suitable characteristic. Also, in case of electrical characteristic, sample KS has excellent capacity.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.523-530
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• 2012

We investigated the experimental method that uses the homogeneous precipitation method to prepare mica flakes-coated rutile-type titania pearlescent pigment with urea as a precipitant. $TiO_2$ particles exhibit a high reflection of lights and optical properties with chemical stabilities, so they are appropriate for coating on luminescent pigments (mica). The coating principle of mi ca coated titania with various thicknesses was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tested by spectrophotometer. Mica with a particle size in the range of $40-60{\mu}m$ was suspended in water, and metal sulphates and urea were added to the mixture, which was heated to boiling. The change in pH was continuously followed. The metal oxide and crystal structure were affected by the conditions of $TiOSO_4$ concentration and reaction time with a sintering temperature the range of $800-1100^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.21 no.12
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• pp.1193-1198
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• 2000

The preparation of nanocrystalline hematite, ${\alpha}-Fe_2O_3$, paricles and their surface coating with silica layers are described. The hematite particles with the size of 30~60 nm are firstly prepared by thermal decomposition of trinuclear acetate-hydroxo iron (III) nitrate complex, $[Fe_3$(OCOCH_3)_7$OH${\cdot}$2H_2O]NO_3$, at $400^{\circ}C$. Subsequently the hematite surfaces are coated with siliva layers by a controlled hydrolysis and condensation reaction of TEOS with varying the TEOS concentration and pH. Monodispersed and spherical $SiO_2-coatedFe_2O_3$ particles with the average particle diameter of ~90 nm and extremely narrow size distribution can be obtained at the pH of 11 and the TEOS concentration of 0.68M, which are found to be the optimum conditions in the present study in achieving the homogeneous deposition of silica layers on hematite surfaces. Diffuse reflectance UV-Vis spectra reveal that the characteristic optical reflectance of ${\alpha}-Fe_2O_3$ particles is preserved almost constant even after coating the surfaces, suggesting that the $SiO_2$ layers can be regarded as protecting layers without degrading the optical properties of hematite particles.

• Journal of Magnetics
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• v.21 no.4
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• pp.622-628
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• 2016

Magnetization property is a critical factor for magnetorheological fluids (MRFs) to achieve the liquid-solid transition. The main focus of this study is on exploring the influence factors on magnetization properties of MRFs. In this paper, a theoretical analysis is performed to discuss the magnetization characteristics of MRFs firstly. Then, a method for the preparation of carbonyl iron-based MRFs is illustrated and five MRFs samples with various material parameters are prepared. It is succeeded by a series of experiments on testing the hysteresis loop and the magnetization curve of each sample and the influence factors are compared and analyzed. Experimental results indicate that there is basically no hysteresis phenomenon on MRFs which exhibits superparamagnetic behavior at room temperature. A surfactant coating on magnetic particles can slightly improve the MRFs magnetization. Additionally, the magnetic susceptibility and the saturation magnetization both increase with the particle concentration, whereas the influence of particle diameter is relatively very small. Moreover, as the temperature increases, the magnetization decreases and the declining rate accelerates gradually.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1351-1355
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• 2018

The photocurrent characteristics of zinc-oxide (ZnO) thin-film transistors (TFTs) prepared using radio-frequency sputtering and spin-coating methods were investigated. Various characterization methods were used to compare the physical and the chemical properties of the sputtered and the spin-coated ZnO films. X-ray photoelectron spectroscopy was used to investigate the chemical composition and state of the ZnO films. The transmittance and the optical band gap were measured by using UV-vis spectrometry. The crystal structures of the prepared ZnO films were examined by using an X-ray diffractometer, and the surfaces of the films were investigated by using scanning electron microscopy. ZnO TFTs were prepared using both sputter and solution processes, both of which showed photocurrent characteristics when illuminated by light. The sputtered ZnO TFTs had a photoresponsivity of 3.08 mA/W under illumination with 405-nm light while the solution-processed ZnO TFTs had a photoresponsivity of 5.56 mA/W. This study provides useful information for the development of optoelectronics based on ZnO.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.813-818
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• 2010

In current automobile and electronic industries, the use of magnesium alloys where both energy and weight saving are attainable is increasing. Despite their light weight, there has been an inherent drawback arising from the surface vulnerable to be oxidized with ease, specifically under corrosive environments. To protect magnesium alloy from corrosion, the present work deals with the electrochemical response of the oxide layer on magnesium alloy specimen prepared by plasma electrolytic oxidation (PEO) method in an electrolyte with zirconia powder. Surface observation using scanning electron microscopy evidences that a number of zirconia particles are effectively incorporated into oxide layer. From the results of potentio-dynamic tests in 3.5 wt% NaCl solution, the PEO-treated sample containing zirconia particles shows better corrosion properties than that without zirconia, which is the result of zirconia incorporation into the coating layer. Corrosion resistance is also measured by utilizing salt spray tests for 120 hrs.

• Journal of the Semiconductor & Display Technology
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• v.20 no.2
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• pp.43-50
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• 2021

The properties of materials which are widely used in industry fields like automobile, shipbuilding, casting, and electronics are strongly needed to have higher surface hardness, lower surface roughness, and higher compressive residual stress. As mentioned above, for the purpose of satisfying three factors, a variety of researches with respect to surface improvement have been actively studied and applied to every industry. SKD61 which is mostly used for die casting process of cold chamber method must meet a countless number of problems which are thermal, mechanical and chemical from highly specific working environment at high temperature over 600℃. Above all, in case of plunger sleeves used for die casting process, thermal fatigue has a bad effect on the surface of an inlet where molten metal is repeatedly injected. On account of it, plunger sleeves cause manufacturers to deteriorate quality of products. Therefore, in this paper, to improve the surface of an inlet of plunger sleeve, multilayer PVD coating using Ti, Cr and Mo is suggested. Furthermore, The surface characteristics such as surface roughness(Rsa, Rsq), surface hardness(HRB, HRC) and residual stress using XRD(X-ray diffractometer) of coated samples and specimens are studied and discussed.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.29-38
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• 2022

In offshore installations, fires cause the structure to lose its rigidity and it leads to structural integrity and stability problems. The Passive Fire Protection (PFP) system slows the transfer rate of fire heat and helps prevent the collapse of structures and fatality. Especially, intumescent epoxy coating is widely used in the offshore industry, and not only is the material cost expensive, but it also takes a lot of time and cost for construction. Several studies have been conducted on the efficient application and optimal design of the PFP system. However, the mechanical properties and the strength of the PFP material have not been considered. In addition, researches on the correlation between the thickness of PFP and the structural behavior were insufficient. Therefore, this study aims to analyze the thermal and mechanical effects of the PFP on the structure when it is applied to the structural member. In particular, it is intended to resolve the change in strength characteristics of the structural members as the thickness of the PFP increases.