• Nanomaterials
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• v.12 no.7
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• pp.1158-1168
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• 2022

Commercial lithium-ion batteries using liquid electrolytes are still a safety hazard due to their poor chemical stability and other severe problems, such as electrolyte leakage and low thermal stability. To mitigate these critical issues, solid electrolytes are introduced. However, solid electrolytes have low ionic conductivity and inferior power density. This study reports the optimization of the synthesis of sodium superionic conductor-type Li_1.5Al_0.3Si_0.2Ti_1.7P_2.8O₁₂ (LASTP) solid electrolyte. The as-prepared powder was calcined at 650 ℃, 700 ℃, 750 ℃, and 800 ℃ to optimize the synthesis conditions and yield high-quality LASTP powders. Later, LASTP was sintered at 950 ℃, 1000 ℃, 1050 ℃, and 1100 ℃ to study the dependence of the relative density and ionic conductivity on the sintering temperature. Morphological changes were analyzed using field-emission scanning electron microscopy (FE-SEM), and structural changes were characterized using X-ray diffraction (XRD). Further, the ionic conductivity was measured using electrochemical impedance spectroscopy (EIS). Sintering at 1050 ℃ resulted in a high relative density and the highest ionic conductivity (9.455 × 10^-4 S cm^-1). These findings corroborate with the activation energies that are calculated using the Arrhenius plot. Therefore, the as-synthesized superionic LASTP solid electrolytes can be used to design high-performance and safe all-solid-state batteries.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.230.1-230.1
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• 2015

One of the major problems of biological ToF-SIMS imaging is the lack of protein and peptide imaging. Most of biological story telling is mianly based on proteins. The biological implication of lipid ToF-SIMS imaging would be much higher if protein imaging is provided together. Utilizing high secondary ion yields of metals, proteins can be ToF-SIMS imaged with nanoparticle tagged proteins. Nanoparticles such as Fe3O4, SiO2, PbS were used for imaing NeuN, MCH, Orexin A, ${\alpha}$ synucline, TH(Tryosine Hydroxylase) in mouse tissues with a spatial resolution of ${\sim}2{\mu}m$ using a TOF-SIMS. Lipids and neurotransmitters images obtained simultaneously with protein images were overlayed for more deeper understanding of neurobiology, which is not allowed by any other bioimaging technqiues. The protein images from TOF-SIMS were compared with confocal fluorescence microscopy and NanoSIMS images. A new sample preparation method for imaging single cell membranes in a tissue using the vibrotome technique to prepare a tissue slice without any fixation and freeze drying will be also presented briefly for Hippocampus and Hypothalamus tissues.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1127-1130
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• 2013

Formation of the monodisperse submicrospheres consisting of ionic palladium(II) complexes, $[(Me_4en)Pd(L)]_2(X)_4$($Me_4en$ = N,N,N',N'-tetramethylethylenediamine; L = bis(4-(4-pyridylcarboxyl)phenyl)methane; $X^-=BF_4{^-}$ and $ClO_4{^-}$), has been carried out without any templates or additives. The submicrospheres were coated with silicates, and then calcined in air at $550^{\circ}C$ for 1 h, to efficiently form hollow-spherical $SiO_2$ submicro-reactors dotted with palladium(0) nanoparticles (PdNPs). That is, the submicrospheres act as both a template and a source of the palladium metal nanoparticles. The submicro-reactors containing nano-catalysts have been characterized by means of SEM, TEM, and XPS. Notably, the reactors were proved to be very effective for Suzuki-Miyaura cross-coupling and hydrogenation reactions.

• Advances in materials Research
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• v.1 no.1
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• pp.93-107
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• 2012

Epoxy resin is widely used in high voltage apparatus as insulation. Fillers are often added to epoxy resin to enhance its mechanical, thermal and chemical properties. The addition of fillers can deteriorate electrical performance. With the new development in nanotechnology, it has been widely anticipated that the combination of nanoparticles with traditional resin systems may create nanocomposite materials with enhanced electrical, thermal and mechanical properties. In the present paper we have carried out a comparative study on dielectric properties, space charge and dielectric breakdown behavior of epoxy resin/nanocomposites with nano-fillers of $SiO_2$ and $Al_2O_3$. The epoxy resin (LY556), commonly used in power apparatus was used to investigate the dielectric behavior of epoxy resin/nanocomposites with different filler concentrations. The epoxy resin/nanocomposite thin film samples were prepared and tests were carried out to measure their dielectric permittivity and tan delta value in a frequency range of 1 Hz - 1 MHz. The space charge behaviors were also observed by using the pulse electroacoustic (PEA) technique. In addition, traditional epoxy resin/microcomposites were also prepared and tested and the test results were compared with those obtained from epoxy resin/nanocomposites.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.5
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• pp.409-417
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• 2016

It is well known that Morpho butterflies show distinctive, brilliant and iridescent colors and have micro-nano scale structures, instead of dyes and pigments, on their wings. This structural coloration is regarded as a novel technique to express color with a long lifetime, ease and precise tenability. Here, we studied optical multilayer thin films with thickness of several tens of nm ($TiO_2$ and $SiO_2$) and lens-shape micro-patterns. Fabrication and characterization of the multilayer stacking structure and the micro-pattern structure were performed and the films were analyzed via several optical measuring techniques. Finally, we discussed how the micro-pattern structure could enhance independence with color changes according to the viewing angle.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.242-248
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• 2009

Forsterite is a crystalline magnesium silicate with chemical formula $Mg_2SiO_4$, which has extremely low electrical conductivity that makes it an ideal substrate material for electronics. In this study, forsterite precursors were synthesized with magnesium silicate gels from the mixture of magnesium nitrate solution and various sodium silicate solution by the geopolymer technique. Precursors and heattreated powders were characterized by thermogravimetrical differential thermal analyzer(TG-DTA), X-ray diffractometer(XRD), scanning electron microscopy(SEM), Si magic angle spinning nuclear magnetic resonance(MAS-NMR), transmission electron microscopy(TEM). As the result of analysis about the crystallization behavior by DTA, the synthesized precursors were crystallized in the temperature range of $700^{\circ}C$ to $900^{\circ}C$. The XRD results showed that the gel composition began to crystallize at various temperature. Also, it was found that the sodium orthosilicate based precursors(named as 'FO') began to crystallize at above $550^{\circ}C$. The FO peaks were much stronger than sodium silicate solution based precursors(named as 'FW'), sodium metasilicate based precursors(named as 'FM') at $800^{\circ}C$. TEM investigation revealed that the 100nm particle sized sample was obtained from FO by heating up to $800^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.241.1-241.1
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• 2013

최근 고집적화된 금속-산화막 반도체 metal oxide semiconductor (MOS) 소자는 크기가 점점 작아짐에 따라 얇은 산화막과 다양한 High-K 물질과 전극에 대하여 연구되고 있다. 이러한 소자의 열적 안정성과 균일성을 얻기 위해 다양한 열처리 방법이 사용되고 있으며, 일반적인 열처리 방법으로는 conventional thermal annealing (CTA)과 rapid thermal annealing (RTA)이 많이 이용되고 있다. 본 실험에서는 microwave radiation에 의한 열처리로 소자의 특성을 개선시킬 수 있다는 사실을 확인하였고, 상대적으로 $100^{\circ}C$ 이하의 저온에서도 공정이 이루어지기 때문에 열에 의한 소자 특성의 열화를 억제할 수 있으며, 또한 짧은 처리 시간 및 공정의 단순화로 비용을 효과적으로 절감할 수 있다. 본 실험에서는 metal-oxide-silicon (MOS) 구조의 capacitor를 제작한 다음, 기존의 CTA나 RTA 처리가 아닌 microwave radiation을 실시하여 MOS capacitor의 전기적인 특성에 미치는 microwave radiation 효과를 평가하였다. 본 실험은 p-type Si 기판에 wet oxidation으로 300 nm 성장된 SiO2 산화막 위에 titanium/aluminium (Ti/Al) 금속 전극을 E-beam evaporator로 형성하여 capacitance-voltage (C-V) 특성 및 current-voltage (I-V) 특성을 평가하였다. 그 결과, microwave 처리를 통해 flat band voltage와 hysteresis 등이 개선되는 것을 확인하였고, microwave radiation 파워와 처리 시간을 최적화하였다. 또한 일반적인 CTA 열처리 소자와 비교하여 유사한 전기적 특성을 확인하였다. 이와 같은 microwave radiation 처리는 매우 낮은 온도에서 공정이 이루어짐에도 불구하고 시료 내에서의 microwave 에너지의 흡수가 CTA나 RTA 공정에서의 열에너지 흡수보다 훨씬 효율적으로 이루어지며, 결과적으로 산화막과 실리콘 기판의 계면 특성 개선에 매우 효과적이라는 것을 나타낸다. 따라서, microwave radiation 처리는 향후 저온공정을 요구하는 nano-scale MOSFET의 제작 및 저온 공정이 필수적인 display 소자 제작의 해결책으로 기대한다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1599-1600
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• 2011

현재 사용되는 전력기기와 전기에너지로 구동되는 기기등은 환경 조화와 에너지 절약을 목표로 고전압 대용량화, 축소 소형화 및 고효율화가 진행되는 과정에 있다. 이런 기기들은 전위를 유지하기 위해서 전기절연기술이 필수적이다. 특히 전기절연재료의 역할이 중요해서 재료의 특성이 기기전체의 종합성능을 지배하기도 한다. 본 연구에서는 몰드 변압기의 절연수지로 사용되는 에폭시 복합체와 마이크로 $SiO_2$와 Ag 각 시편의 열팽창률과 유전 특성 및 온도에 따른 절연파괴강도를 측정하여 열적 특성 및 전기적 특성을 검토하고 분석한다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.32-39
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• 2008

Tunnel oxide of non-volatile memory (NVM) devices would be very difficult to downscale if ten-year data retention were still needed. This requirement limits further improvement of device performance in terms of programming speed and operating voltages. Consequently, for low-power applications with Fowler-Nordheim programming such as NAND, program and erase voltages are essentially sustained at unacceptably high levels. A promising solution for tunnel oxide scaling is tunnel barrier engineering (TBE), which uses multiple dielectric stacks to enhance field-sensitivity. This allows for shorter writing/erasing times and/or lower operating voltages than single $SiO_2$ tunnel oxide without altering the ten-year data retention constraint. In this paper, two approaches for tunnel barrier engineering are compared: the crested barrier and variable oxide thickness. Key results of TBE and its applications for NVM are also addressed.

• Journal of the Korean Ceramic Society
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• v.45 no.7
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• pp.401-404
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• 2008

Willemite ($Zn_2SiO_4$) are a wide range of applications such as a phosphor host and an important crystalline phase in glass ceramics, electrical insulators, glazes, and pigments. In this study, Willemite precursors were synthesized with zinc silicate gels from mixture of zinc nitrate solution and various sodium silicate solution by the geopolymer technique. To examine the crystallization behavior, precursors were have been monitored by the XRD. A pure willemite phase was obtained at $900^{\circ}C$. TEM investigations revealed that the sample with 50 nm particle size was obtained via heat-treated at $900^{\circ}C$ for W-3.