• 한국세라믹학회지
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• 제34권7호
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• pp.685-692
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• 1997

Effects of sintering temperature and time on the phase formation, the characteristics of sintering and electrical behaviors of NASICON compounds with Na3Zr2Si2PO12 and Na3.2Zr1.3Si2.2P0.8O10.5 compositions synthesized by solid state reaction were investigated. Maximum relative densities of 96% and 91% were obtained for Na3Zr2Si2PO12 and Na3.2Zr1.3Si2.2P0.8O10.5 compounds, respectively. Complex impedance analysis in a frequency range below 4 MHz was performed to measure the ionic conductivity and migration barrier height of the compounds at RT-30$0^{\circ}C$. The maximum ionic conductivity and the minimum migration barrier height were 0.45 ohm-1cm-1 and 0.07 eV, respectively. The migration barrier height of the high temperature form (space group : R3c) is about 30-40% of that of the low temperature form (space group : C2/c) in two NASICON compounds. Ionic conductivity increases with increasing sinterability, and the presence of glass phase in Na3.2Zr1.3Si2.2P0.8O10.5 compounds lowers significantly ionic conductivity at temperatures above 14$0^{\circ}C$.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1437-1439
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• 2009

Electrical and optical properties of $SiO_2$-doped ZnO (SZO) films on the corning 7059 glass substrates by using rfmagnetron sputtering method are investigated. The deposition rate becomes maximum near 3 wt.% and gradually decreases when the $SiO_2$ content further increases. The growth rates at 3 wt.% is $4^{\circ}$A/s. We found that the average transmittance of all films is over 80% in the wavelength range above 500 nm. The optical band gap decreases from 3.52 to 3.33 eV with an increase in thickness. X-ray diffraction patterns show that the film with a relatively low $SiO_2$ content (< 4 wt.%) is amorphous. SZO films at the $SiO_2$ contents of 2 wt.% shows the resistivity of about $3.8{\times}10^{-3}{\cdot}cm$. The sheet resistance decreases with increasing the heat treatment temperature.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.190-190
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• 2010

Zinc oxide is the most attractive material due to the large direct band gap (3.37 eV), excellent chemical and thermal stability, and large exciton binding energy (60 meV). Recently, ZnO nanorods were used as the high efficient antireflection coating layer of solar cells based on silicon (Si). In this reports, we studied the effects of rapid thermal annealing (RTA) treatment on optical properties of ZnO nanorods. For fabrication of ZnO nanorods, there are many methods such as hydrothermal method, sol-gel method, and metal organic chemical vapor deposition method. Among of them, we used the conventional wet chemical method which is simple and low temperature growth. In order to synthesize the ZnO nanorods, the ZnO films were deposited on Si substrate by RF magnetron sputtering at room temperature and the samples were dipped to aqua solution containing the zinc nitrate and hexamethylentetramines (HMT). The synthesis process was achieved in keeping with temperature of $90-95^{\circ}C$ and under constant stirring. The morphology of ZnO nanorods on glass and Si was characterized by scanning electron microscopy. For the analysis of antireflection performance, the reflectance and transmittance were measured by spectrophotometer. And for analyzing the effects of RTA treatment on ZnO nanorods, crystalline properties were investigated by X-ray diffraction measurements and optical properties was estimated by photoluminescence spectra.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.283-290
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• 2019

In global competition manufacturing companies have to produce modern, new constructions from advanced materials in order to increase competitiveness. The aim of my research was to develop a new composite cellular plate structure, which can be primarily used for structural elements of road, rail, water and air transport vehicles (e.g. vehicle bodies, ship floors). The new structure is novel and innovative, because all materials of the components of the newly developed structure are composites (laminated Carbon Fiber Reinforced Plastic (CFRP) deck plates with pultruded Glass Fiber Reinforced Plastic (GFRP) stiffeners), furthermore combines the characteristics of sandwich and cellular plate structures. The material of the structure is much more advantageous than traditional steel materials, due mainly to its low density, resulting in weight savings, causing lower fuel consumption and less environmental damage. In the study the optimal construction of a given geometry of a structural element of a road truck trailer body was defined by single- and multi-objective optimization (minimal cost and weight). During the single-objective optimization the Flexible Tolerance Optimization method, while during the multi-objective optimization the Particle Swarm Optimization method were used. Seven design constraints were considered: maximum deflection of the structure, buckling of the composite plates, buckling of the stiffeners, stress in the composite plates, stress in the stiffeners, eigenfrequency of the structure, size constraint for design variables. It was confirmed that the developed structure can be used principally as structural elements of transport vehicles and unit load devices (containers) and can be applied also in building construction.

• Coupled systems mechanics
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• 제11권1호
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.

• 전자공학회논문지
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• 제51권6호
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• pp.71-77
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• 2014

본 연구에서는 radio frequency(rf) 마그네트론 스퍼터링 기술을 이용하여 Corning 유리 기판에 증착된 InGaZnO (IGZO) 박막의 광 투과도 특성에 고 에너지 전자빔 조사(high-energy electron beam irradiation (HEEBI))이 미치는 영향을 연구하였다. 저온에서 증착된 IGZO 박막은 공기 중 과 상온 조건에서 0.8 MeV의 전자빔 에너지와 $1{\times}10^{14}-1{\times}10^{16}electrons/cm^2$ dose를 사용하여 HEEBI 처리 되었다. IGZO 박막의 광 투과도는 utraviolet visible near-infrared spectrophotometer (UVVIS)로 측정되었다. HEEBI 처리 된 IGZO/유리 이중층의 총 광 투과도에서 HEEBI 처리된 IGZO 단일막 만의 광 투과도를 분리하는 방법을 상세히 연구하였다. 실험 결과로부터 $1{\times}10^{14}electrons/cm^2$의 적절한 dose로 처리된 HEEBI가 IGZO 박막의 투명도를 극대화시킴을 알 수 있었다. 또한 이렇게 적절한 dose로 처리된 HEEBI가 광학 밴드갭($E_g$)을 3.38 eV에서 3.31 eV로 감소시킴을 알 수 있었다. 이러한 $E_g$의 감소는 적절한 dose로 공기 중 상온에서 처리된 HEEBI가 진공 중 고온에서 처리된 열적 annealing 효과와 유사함을 제시하고 있다.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.479-485
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• 2022

At the Korea Institute of Radiological and Medical Sciences, physical human phantoms were developed to evaluate various radiation protection quantities, based on the mesh-type reference computational phantoms of the International Commission on Radiological Protection. The physical human phantoms were fabricated such that a radiophotoluminescent glass dosimeter (RPLGD) with a Tin filter, namely GD-352M, could be inserted into them. A Tin filter is used to eliminate the overestimated signals in low-energy photons below 100 keV. The measurement uncertainty of the RPLGD reader system based on GD-352M should be analyzed for obtaining reliable protection quantities before using it for practical applications. Generally, the measurement uncertainty of RPLGD systems without Tin filters is analyzed for quality assurance of radiotherapy units using a high-energy photon beam. However, in this study, the measurement uncertainty of GD-352M was analyzed for evaluating the protection quantities. The measurement uncertainty factors in the RPLGD include the reference irradiation, regression curve, reproducibility, uniformity, energy dependence, and angular dependence, as described by the International Organization for Standardization (ISO). These factors were calculated using the Guide to the Expression of Uncertainty in Measurement method, applying ISO/ASTM standards 51261(2013), 51707(2015), and SS-ISO 22127(2019). The measurement uncertainties of the RPLGD reader system with a coverage factor of k = 2 were calculated to be 9.26% from 0.005 to 1 Gy and 8.16% from 1 to 10 Gy. A blind test was conducted to validate the RPLGD reader system, which demonstrated that the readout doses included blind doses of 0.1, 1, 2, and 5 Gy. Overall, the E_n values were considered satisfactory.

• 한국산학기술학회논문지
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• 제14권2호
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• pp.846-849
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• 2013

$TiO_2$ 박막을 저온 열처리 졸-겔 법으로 합성하였다. 박막의 기판은 면적이 $100mm^2$인 붕규산염 유리를 사용하여 시료를 $300^{\circ}C$부터 $1100^{\circ}C$까지 열처리하였고, 이때 제조된 박막의 두께는 약 $1.5{\mu}m$정도였다. $300^{\circ}C$에서 2시간 동안 열처리한 $TiO_2$ 박막은 아나타제 상을 나타내었고 열처리 온도가 증가함에 따라 비정질 상태에서 아나타제상과 루타일 상이 공존하면서 각 상의 분율이 변화하였다. SEM 분석에 의하면 박막의 입자 크기는 $0.1{\sim}0.54{\mu}m$이었으며 Uv-visible 반사특성에 있어서 390nm부근에서 광흡수가 되는 것을 알 수 있었다. 따라서 낮은 열처리 온도에서 생성된 $TiO_2$ 박막은 주로 아나타제 상을 가지며 광촉매 특성을 2.4배 증가시키는 것으로 나타났다.

• 한국진공학회지
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• 제18권5호
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• pp.384-389
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• 2009

ZnO는 육방정계결정구조의 물질로서 3.37 eV의 넓은 띠 간격과 60 meV의 큰 exciton 결합에너지에 따른 높은 효율의 자외선발광으로 짧은 파장의 빛 (녹, 청, 자외선)을 내는 LED (Light Emitting Diode) 분야에서 관심을 기울이고 있는 물질이다. LED제작을 위해서는 n형의 ZnO와 p형의 ZnO가 필요하지만 기본적으로 ZnO은 n형이므로 신뢰성 있는 p형 ZnO박막을 제작하기 위한 노력이 기울여지고 있다. 본 연구에서는 ALD (Atomic Layer Deposition)로 제작된 ZnO박막에 20 keV의 에너지를 갖는 질소이온을 $10^{13}{\sim}10^{15}ions/cm^2$로 조사한 후 Hall 효과 측정장치를 이용하여 질소이온 조사에 따른 전기적 특성변화를 조사하였다.

• 폴리머
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• 제33권6호
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• pp.530-536
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• 2009

고리지방족 에폭시와 산무수물 경화제계에 탄소단섬유(SCF)와 유리단섬유(SGF)를 첨가하여 복합재를 제조한 다음 이들의 열적/기계적 특성을 조사하였다. 열기계분석법으로 측정된 열팽창계수(CTE)의 감소 효과를 보면 낮은 단섬유 함량에서는 두 섬유가 거의 비슷하나, 함량이 증가하면 SCF가 SGF에 비해 훨씬 효과적이었다. SCF 강화 복합재에 대한 CTE 실험값을 이론식에 적용해 본 결과 함량이 낮을 때는 혼합법칙(mixture rule)에 잘 맞으며, 함량이 높아지면 Craft-Christensen 식에 근접하였다. 또한, 유리상($30^{\circ}C$과 고무상($180^{\circ}C$)에서의 저장탄성률은 단섬유를 첨가하였을 때 크게 증가하였다. 전자주사현미경(SEM)으로 파단면을 관찰하여본 결과 이와 같은 결과는 단섬유와 에폭시 매트릭스간의 계면접착력과 밀접한 관계가 있음을 알 수 있었다.