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Han, Wooje,Yoo, Byungwook,Kwon, Kwang-Ho,Cho, Hyung Hee,Park, Hyung-Ho Elsevier 2016 THIN SOLID FILMS - Vol.619 No.-
<P><B>Abstract</B></P> <P>Poly(vinylidenefluoride-<I>co</I>-hexafluoropropylene) (PVdF-HFP) nanocomposites were prepared with fluorinated barium titanate (BaTiO<SUB>3</SUB>) nanoparticles. BaTiO<SUB>3</SUB> nanoparticles was treated with 2,2,2-trifluoroacetic acid in Novec-7500 and the modified surface characteristics of the nanoparticles showed good solubility in the fluorous solvent and fluorous polymer. The optimized fluorinated BaTiO<SUB>3</SUB> condition had explored by controlling temperature and ligand ratio. The prepared nanocomposite through fluorinated nanoparticles were characterized by using Fourier transform infrared spectroscopy, X-ray diffraction, impedance spectroscopy and atomic force microscopy in order to investigate their structural and electrical properties. Root mean square roughness of nanocomposites was increased only 0.48nm after adding 20vol.% of fluorinated BaTiO<SUB>3</SUB> nanoparticles. Also, dielectric constant of nanocomposite was predicted and agreed well with experimental data through the modified Kerner model. Dielectric constant of PVdF-HFP nanocomposite was increased about 15 thorough an addition of 20vol.% of fluorinated BaTiO<SUB>3</SUB> nanoparticles. The application of near edge X-ray absorption fine structure spectroscopy of PVdF-HFP/fluorinated BaTiO<SUB>3</SUB> nanocomposites was presented.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Trifluoroacetic acid was used for the fluorination of BaTiO<SUB>3</SUB> nanoparticles. </LI> <LI> Polymer nano-composites were prepared with fluorinated nanoparticles. </LI> <LI> Roughness of composite was relieved by 40 times compared without fluorination. </LI> <LI> Dielectric constant of composites was almost the same with the calculated one. </LI> </UL> </P>
Han, Wooje,Yoo, Byungwook,Park, Hyung-Ho Hindawi Limited 2016 Journal of nanomaterials Vol.2016 No.-
<P>Barium titanate (BaTiO3: BTO) nanoparticles (NPs) were synthesized by chlorine-free ambient condition sol (ACS) process using heat reflux at low temperature of 90°C. The size distribution and morphology of BTO NPs were investigated by varying the concentration of tetrabutylammonium hydroxide (TBAH). The crystalline size of BTO NPs was decreased with increasing the amount of TBAH capping agent (average size changes from 54.3 to 38.7 nm for 0 to 0.5 M TBAH in X-ray diffraction measurement). The particle size of BTO NPs was principally controlled by a synthetic control of butyl chain of TBAH and also a steric effect of excess amount of TBAH. The dielectric constant of BTO NPs was decreased from 152 to 144 at 1 MHz after an adoption of TBAH capping agent with almost uniform dielectric loss (<0.027). But the dielectric constant of BTO NPs synthesized with various molar ratio of TBAH (0.1, 0.3, and 0.5) did not show a distinguished decrease. At the particle size range in this experiment, the dielectric behavior of BTO NPs was found to be mainly dependent on the TBAH ligands at BTO NPs formed during capping process, not on the size of BTO NPs.</P>
Wooje Han,Jiwan Kim,Hyung‑Ho Park 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.2
Barium titanate nanocrystals were synthesized via an ambient-condition-sol (ACS) process using low temperature heat reflux. The prepared nanocrystals were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, particle size analysis, and capacitance–voltage measurements to investigate their crystal structure, chemical bonding, size distribution, and structural, dielectric, and electrical properties. The ACS process was carried out at temperatures lower than 100 °C to avoid the agglomeration of the nanocrystals. Because of the low temperature used in this study, small barium titanate nanocrystals were obtained (average size ranged from 280 to 120 nm). The bigger barium titanate nanocrystals showed higher dielectric constant than the smaller ones (size of up to 140 nm).
Han, Wooje,Lee, Hong-Sub,Yoo, Byungwook,Park, Hyung-Ho Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-
<P><B>Abstract</B></P> <P>Crystalline barium titanate (BaTiO<SUB>3</SUB>) nanoparticles were synthesized by refluxing in an air atmosphere at a low temperature using sodium hydroxide. The reaction mechanism of BaTiO<SUB>3</SUB> nanoparticle formation by this new liquid–solid–solution (LSS) synthesis route with refluxing in an air atmosphere at a low temperature of 80 °C was demonstrated to be a facile fabrication process for BaTiO<SUB>3</SUB> nanoparticles with a high crystalline quality and minimized agglomeration rate. BaTiO<SUB>3</SUB> nanoparticles were formed via sodium titanate (Na<SUB>2</SUB>TiO<SUB>3</SUB>), and the size of the BaTiO<SUB>3</SUB> nanoparticles decreased with increasing sodium hydroxide concentration. The formation of a Na<SUB>2</SUB>TiO<SUB>3</SUB> intermediate phase was confirmed by energy dispersive X-ray spectroscopy and X-ray diffraction analysis. The capping ligands of BaTiO<SUB>3</SUB> suggest that hydroxyl and oleic acid are present. The dielectric constant of the crystalline BaTiO<SUB>3</SUB> nanoparticles was higher than 150.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pure crystalline BaTiO<SUB>3</SUB> nanoparticles were synthesized by new synthesis route. </LI> <LI> BaTiO<SUB>3</SUB> nanoparticles were synthesized at 80 °C through refluxing in air atmosphere. </LI> <LI> BaTiO<SUB>3</SUB> nanoparticles were formed through Na<SUB>2</SUB>TiO<SUB>3</SUB> as a chemical intermediate. </LI> <LI> The concentration of NaOH plays an important role to BaTiO<SUB>3</SUB> phase formation. </LI> <LI> The concentration of NaOH plays an important role to control the size of BaTiO<SUB>3</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
100 MeV 양성자가속기를 활용한 SRAM SEE(Static Random Access Memory Single Event Effect) 시험 연구
Wooje Han,Eunhye Choi,Kyunghee Kim,Seong-Keun Jeong 한국우주과학회 2023 우주기술과 응용 Vol.3 No.4
본 연구는 국내 100 MeV 양성자가속기와 우주부품시험센터 우주전문시험시설기반을 활용하여 우주부품의우주 방사선환경 시험검증 기술을 개발하고자 한다. 우주개발의 진전에 따라 고도화된 위성의 임무는 위성의핵심부품인 메모리 등에 고집적 회로를 필수적으로 사용하고, 태양전지, 광학센서 및 opto-electronics 등부수 장치에 반도체 소자의 활용이 증가하고 있다. 특히, 전자부품을 우주에 적용하기 위해서는 우주환경 시험을 반드시 거쳐야 하며, 그 중 가장 중요한 것이 고 에너지 방사선환경에서의 우주부품시험이다. 따라서 이에 필요한 우주 방사선 환경 구현 시설을 갖추어 체계적인 시험절차를 수립할 필요가 있다. 한국산업기술시험원 우주부품시험센터는 메모리 부품에 대한 방사선 시험 장치를 제작하고 이를 이용한 메모리 방사선 영향평가 시험을 수행하였다. 경주양성자가속기에서 100 MeV 양성자를 활용하여 한국에서 활용가능한 수준의방사선 시험을 진행하였다. 이러한 시험을 통해 메모리 반도체에서 나타나는 single event upset을 관찰할수 있었다. 향후 해당 시험을 체계화하여 우주산업화에 기반을 마련하고자 한다. This study aims to develop technology for testing and verifying the space radiation environment of miniature space components using the facilities of the domestic 100 MeV proton accelerator and the Space Component Test Facility at the Space Testing Center. As advancements in space development progress, high-performance satellites increasingly rely on densely integrated circuits, particularly in core components components like memory. The application of semiconductor components in essential devices such as solar panels, optical sensors, and opto-electronics is also on the rise. To apply these technologies in space, it is imperative to undergo space environment testing, with the most critical aspect being the evaluation and testing of space components in high-energy radiation environments. Therefore, the Space Testing Center at the Korea testing laboratory has developed a radiation testing device for memory components and conducted radiation impact assessment tests using it. The investigation was carried out using 100 MeV protons at a low flux level achievable at the Gyeongju Proton Accelerator. Through these tests, single event upsets observed in memory semiconductor components were confirmed.
2륜 독립조향 steer-by-wire 시스템의 제어기 개발
성우제(Wooje Sung),오승규(Seungkyu Oh),김창준(Changjun Kim),한창수(Changsoo Han),이언구(Unkoo Lee),이상호(Sangho Lee),조희영(Heeyoung Cho) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In this study, the controller of a SBW (Steer-by-Wire) system was developed. As a SBW system is applied in order to improve steering feel and maneuverability, the controller should have two aims. One is controlling steering wheel for the driver's steering feel and the other is controlling the front wheel steering linkage for vehicle stability. In order to the tie-rod actuating SBW controller analysis, 6-bar linkage kinematics was investigated. The controller of the tie-rod actuating SBW was used the Ackerman Geometry for improving the vehicle stability. Verification simulation and performance simulation are showed that the SBW controller was available in this study.
Ambient pressure dried tetrapropoxysilane-based silica aerogels with high specific surface area
Parale, Vinayak G.,Han, Wooje,Jung, Hae-Noo-Ree,Lee, Kyu-Yeon,Park, Hyung-Ho Elsevier 2018 Solid state sciences Vol.75 No.-
<P><B>Abstract</B></P> <P>In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)<SUB>4</SUB> family, was reported for the first time. The oxalic acid and NH<SUB>4</SUB>OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH<SUB>4</SUB>OH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optically transparent and hydrophobic silica aerogel using TPOS was successfully synthesized. </LI> <LI> Sol-gel compositional effect using TPOS on the polymerization of aerogels was firstly reported. </LI> <LI> MeOH/TPOS and acid/base concentrations strongly influenced on the physical and textural properties. </LI> <LI> High surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) are obtained using TPOS as precursor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>