• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.32.1-32.1
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• 2010

본 연구에서는 질화물계 발광 다이오드의 광추출효율을 향상시키기 위해서 Bi-layer나노 임프린트 리소그래피와 Lift-off 공정을 이용하여 ITO투명전극 층 상부에 TiO2 나노 패턴을 형성하였다. 발광 다이오드의 투명전극 층 상부에 UV 나노 임프린트 리소그래피를 이용하여 주기적인 폴리머 패턴을 형성한 후 폴리머 패턴 상부에 RF magnetron Sputtering 공법을 이용하여 TiO2를 증착하고 Lift-off 공정을 이용하여 TiO2 나노 패턴을 제작하였다. 그 결과를 주사전사 현미경(SEM)으로 확인한 결과 임프린트 스탬프와 동일한 나노 패턴이 질화물 계 발광다이오드 투명 전극층 표면에 주기적으로 형성되었다. TiO2 나노 패턴 형성을 통한 광추출 효율의 향상 효과를 확인하기 위해 Electroluminescence (EL) 측정한 결과 TiO2 나노 패턴이 형성된 발광다이오드 소자의 EL 강도가 나노 패턴이 없는 발광다이오드와 비교하여 12% 정도 향상 되었음을 보였고, 이는 고 굴절율 나노 패턴이 활성층에서 발생된 빛의 산란 효과를 유도하여 빛의 내부 전반사를 감소시킨 결과로 해석된다. 또한 소자의 전기적 특성평가를 위한 I-V 측정결과, TiO2 나노 패턴이 형성된 발광 다이오드의 전기적 성질이 저하되지 않았음을 확인하였다.

• Polymer(Korea)
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• v.28 no.2
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• pp.170-176
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• 2004

The effect of reaction conditions on the size and size distribution of superparamagnetic iron oxide coated with siloxane was big investigated by using dynamic light scattering. The hydrogen bond between the hydroxyl groups on tile surface of the magnetite and silanol was confirmed by FT-IR. The size of nanoparticles increased with the reaction temperature, but decreased with monomer contents and agitation speeds. There was not a big difference in size of nanoparticles, prepared by different reaction conditions, but its distribution was in the range of 14∼41nm. All samples exhibited the superparamagnetic nature. The magnetic susceptibility of the nanoparticles increased with the reaction temperature while it decreased with the monomer content and agitation speed.

• Journal of Powder Materials
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• v.21 no.6
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• pp.441-446
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• 2014

In this study, we synthesize silica-core gold-satellite nanoparticles (SGNPs) for the surface-enhanced Raman scattering (SERS) based sensing applications. They consist of gold satellite nanoparticles (AuNPs) fixed on the silica core nanoparticles, which sizes of AuNPs can be tunned by varying the amount of reactants (growth solution and reducing agent). Their surface plasmon resonance (SPR) properties were characterized by using UV-vis spectroscopy, showing that the growth of AuNPs on silica cores leads to the light absorption in the longer wavelength region. Furthermore, the size increase of AuNPs exhibited the dramatic change in SERS activity due to the formation of hot spots. The optimized SGNPs showing enhancement factor ${\sim}3.8{\times}10^6$ exhibited a detection limit of rhodamine 6G (R6G) as low as $10^{-8}M$. These findings suggest the importance of size control of SGNPs and their SPR properties to develop highly efficient SERS sensors.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.349-349
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• 2009

High quality ZnO:Al films were prepared on glass substrates by in-line RF magnetron sputtering and their surface morphologies were modified by wet-etching process in dilute acid solution to improve optical properties for application to silicon thin film solar cells as front electrode. The as-deposited films show a strong preferred orientation in [001] direction under our experimental conditions. A low resistivity below $5{\times}10^{-4}{\Omega}{\cdot}cm$ and high optical transmittance above 80% in a visible range are achieved in the films deposited at optimized conditions. After wet-etching, the surface morphologies of the films are changed dramatically depending on the deposition conditions, especially working pressure. The optical properties such as total/diffuse transmittance, haze and angular resolved distribution of light are varied significantly with the surface morphology feature, whereas the electrical properties are seldom changed. The cell performances of silicon thin film solar cells fabricated on the textured films are also evaluated in detail with comparison of commercial $SnO_2$:F films.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1165-1174
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• 2001

The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the acoustic pressure field of a centrifugal fan. If the fan is operating at the free field without the casing, the acoustic analogy is a good method to predict the acoustic of the fan. But, the casing gives a dominant effect to the radiated sound field and the scattering effect of casing should be considered. So, in this paper the Kirchhoff-BEM is developed, which can consider the scattering effect of the rigid body. In order to consider the scattering and diffraction effects owing to the casing, BEM is introduced. The source of BEM is newly developed, so the sound field of the centrifugal fan can be obtained. In order to compare the predicted one with experimental data, a centrifugal impeller and a wedge are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal sound. The radiated acoustic field shows the diffraction and scattering effects of the wedge clearly.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.378-378
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• 2011

ZnO 나노선 구조는 나노선 구조를 통해 입사한 빛을 산란시켜 광흡수를 촉진시키고, 바닥 전극으로 바로 이어진 수직의 1차원 구조를 통해 전자가 빠르게 이동할 수 있으며, 넓은 표면적을 가지고 있는 등의 장점을 가지고 있어 오래전부터 광전소자에 이용되었다. 하지만 ZnO 물질 자체의 밴드갭 에너지가 3.2 eV로 비교적 큰 편이라 가시광 영역의 빛을 흡수, 이용하기 위해서는 작은 밴드갭을 가지는 광감응 물질이 필요하다. 본 연구에서는 저온의 수열합성법을 통해 합성한 ZnO 나노선 구조 상에 Cd 계열의 무기물 양자점을 증착하여 이종구조를 형성하는 방법을 개발하였다. 본 연구에서 사용한 양자점인 CdS와 CdSe는 벌크 밴드갭 에너지가 각각 2.3 eV, 1.7 eV로 가시광 영역의 빛을 흡수할 수 있으며, ZnO 나노선과 type-II 밴드구조를 가지기 때문에 전자-정공 분리 및 포집에 유리하다. 합성된 구조를 이용하여 photoelectrochemical 특성을 분석하였으며, 그 결과 양자점의 증착으로 광전류 생성이 향상됨을 확인하였다. 특히 ZnO 나노선 상에 CdS 양자점 증착 후 추가적으로 CdSe 양자점을 증착하여 다중접합 나노선 구조를 형성한 경우 광전류 생성이 가장 크게 향상된 결과를 확인하였다.

• Korean Journal of Optics and Photonics
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• v.27 no.2
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• pp.61-66
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• 2016

We used transmission deflectometry to measure the three-dimensional shapes of optical components, and we used the Hilbert transform to retrieve the phases from measured deformed fringe images. Deflectometry is useful for measuring large-scale samples, and specular samples. We have retrieved the phases from deformed fringe images and Hilbert-transformed images, and have used the least-squares method to find the height information. We have verified that phase retrieval using Hilbert transform is useful by computer simulation and experiment.

• Solar Energy
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• v.15 no.3
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• pp.141-149
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• 1995

The tungsten oxide thin films were prepared on $s_i$ wafer by using an electron-beam evaporation technique. Thickness and structure of tungsten oxide film degraded in various electrolytes were analyzed by Rutherford backscattering spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscope. Thickness of $WO_3$ film was the most dissolved in 1M $H_2SO_4$ electrolytye. We have confirmed that the degradation of this films was accelerated by $H_2O$ in electrolytes. But the electronic structure of film degraded by electrolyte contained of glycerol was not changed as comparision with as-deposited film. The degradation may be attributed to a change of thickness and the surface morphology of the film.

• Journal of the Korean Chemical Society
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• v.47 no.1
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• pp.7-12
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• 2003

It was recently reported that the SERS effect of the silver mirror substrate made by Tollen's method is much superior to that of other substrates. In this study, the experiments for comparison were done, where we checked the characteristics of silver mirror substrate made by different reductants, time interval and thermal treatments. We also surveyed correlations in substrates changes, the influence of SERS enhancement, and adsorbed orientation of phenol red.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1381-1389
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• 1988

The heat transfer by simultaneous conduction, convection and radiation between flame and fuel surface in a thermally radiating medium is investigated theoretically. The flame and fuel surface are assumed to be diffuse, gray, infinite, isothermal, parallel surfaces separated by a finite distance. The space between the plates is supposed is formulated exactly in terms of simultaneous interior-differential equations. The numerical results reveal the effect of the system parameters on the heat transfer characteristics and the temperature distributions. The numerical results reveal that the optically thick radiating medium has a blocking effect on the total beat transfer. The temperature distributions are observed to be convex upward for an optically thick radiating medium as the alberto decreases.