• 한국재료학회지
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• 제20권12호
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• pp.686-690
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• 2010

$TiO_2$ nanowires were self-catalytically synthesized on bare Si(100) substrates using metallorganic chemical vapor deposition. The nanowire formation was critically affected by growth temperature. The $TiO_2$ nanowires were grown at a high density on Si(100) at $510^{\circ}C$, which is near the complete decomposition temperature ($527^{\circ}C$) of the Ti precursor $(Ti(O-iPr)_2(dpm)_2)$. At $470^{\circ}C$, only very thin (< $0.1{\mu}m$) $TiO_2$ film was formed because the Ti precursor was not completely decomposed. When growth temperature was increased to $550^{\circ}C$ and $670^{\circ}C$, the nanowire formation was also significantly suppressed. A vaporsolid (V-S) growth mechanism excluding a liquid phase appeared to control the nanowire formation. The $TiO_2$ nanowire growth seemed to be activated by carbon, which was supplied by decomposition of the Ti precursor. The $TiO_2$ nanowire density was increased with increased growth pressure in the range of 1.2 to 10 torr. In addition, the nanowire formation was enhanced by using Au and Pt catalysts, which seem to act as catalysts for oxidation. The nanowires consisted of well-aligned ~20-30 nm size rutile and anatase nanocrystallines. This MOCVD synthesis technique is unique and efficient to self-catalytically grow $TiO_2$ nanowires, which hold significant promise for various photocatalysis and solar cell applications.

• Journal of Electrochemical Science and Technology
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• 제11권4호
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• pp.392-398
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• 2020

Producing solar grade silicon using an inexpensive method is a key factor in lowering silicon solar cell costs; the direct electrochemical reduction of SiO₂ in molten salt is one of the more promising candidates for manufacturing this silicon. In this study, SiO₂ granules were electrochemically reduced in molten CaCl₂ (850℃) using Ag-Si eutectic droplets that catalyze electrochemical reduction and purify the Si product. When Ag is used as the working electrode, the Ag-Si eutectic mixture is formed naturally during SiO₂ reduction. However, since the Ag-Si eutectic droplets are liquid at 850℃, they are easily lost during the reduction process. To minimize the loss of liquid Ag-Si eutectic droplets, a cylindrical graphite container working electrode was introduced and Ag was added separately to the working electrode along with the SiO₂ granules. The graphite container working electrode successfully prevented the loss of the Ag-Si eutectic droplets during reduction. As a result, the Ag-Si eutectic droplets acted as stable catalysts for the electrochemical reduction of SiO₂, thereby producing one-dimensional Si rods through a mechanism similar to that of vapor-liquid-solid growth.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.149-149
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• 2016

Ceramic is widely known material due to its outstanding mechanical property. Besides, Zirconia(ZrO2) has a low thermal conductivity so it is advantage in a heat insulation. Because of these superior properties, ZrO2 is attracted to many fields using ultra high temperature for example vehicle engines, aerospace industry, turbine, nuclear system and so on. However brittle fracture is a disadvantage of the ZrO2. In order to overcome this problem, we can make the ceramic materials to the forms of ceramic nanoparticles, ceramic nanowhiskers and these forms can be used to an agent of composite materials. In this work, we selected Au catalyzed Vapor-Liquid-Solid mechanism to synthesize ZrO2 nanowhiskers. The ZrO2 whiskers are grown through Hot-wall Chemical Vapor Deposition(Hot wall CVD) using ZrCl4 as a powder source and Au film as a catalyst. This Hot wall CVD method is known to comparatively cost effective. The synthesis condition is a temperature of $1100^{\circ}C$, a pressure of 760torr(1atm) and carrier gas(Ar) flow of 500sccm. To observe the morphology of ZrO2 scanning electron microscopy is used and to identify the crystal structure x-ray diffraction is used.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.472-473
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• 2008

Flow boiling in parallel microchannels has received attention as an effective heat sink mechanism for power-densities encountered in microelectronic equipment. the bubble dynamics coupled with boiling heat transfer in microchannels is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulation is performed to further clarify the dynamics of flow boiling in microchannels. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle. The method is further extended to treat the no-slip and contact angle conditions on the immersed solid. Also, the reverse flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of channel shape and inlet area restriction on the bubble growth, reverse flow and heat transfer are quantified.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.350.2-350.2
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• 2014

We investigated the structural and optical evolution of Ga2O3 thin films on glass substrates deposited using radio frequency magnetron sputtering. Initially, amorphous Ga2O3 thin film is grown, and then, surface humps and nanowire (NW) bundles are gradually formed as the film thickness increases. The surface humps are Ga-rich and provide nucleation sites for NWs through a self-catalytic vapor-liquid-solid mechanism with self-assembled Ga droplets. Both the surface humps and the NWs induce variation of the optical properties such as the optical bandgap and refractive index by absorbing light in the ultraviolet region.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.291.2-291.2
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• 2013

Growth behavior of b-Ga2O3 nanowires (NWs) on sapphire(0001) substrates during radio-frequency magnetron sputtering is reported. Upon fabrication, flat thin films grew initially, subsequent to which, NW bundles were formed on the surface of thin film with increasing film thickness. This transition of the growth mode occurred only at temperatures greater than ${\sim}450^{\circ}C$. The b-Ga2O3 NWs were grown through the self-catalytic vapor-liquid-solid mechanism with self-assembled Ga seeds. Secondary growth of NWs, which occurred from the sides of primary NWs resulting in branched NW structures, was also observed. Finally, the room temperature photoluminescence properties of as-grown and annealed b-Ga2O3 NW samples were investigated.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.288-288
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• 2013

Lithium-ion battery (LIB) is one of the most important rechargeable battery and portable energy storage for the electric digital devices. In particular, study about the higher energy capacity and longer cycle life is intensively studied because of applications in mobile electronics and electric vehicles. Generally, the LIB's capacity can be improved by replacing anode materials with high capacitance. The graphite, common anode materials, has a good cyclability but shows limitations of capacity (~374 mAh/g). On the contrary, silicon (Si) and germanium(Ge), which is same group elements, are promising candidate for high-performance LIB electrodes because it has a higher theoretical specific capacity. (Si:4200 mAh/g, Ge:1600 mAh/g) However, it is well known that Si volume change by 400% upon full lithiation (lithium insertion into Si), which result in a mechanical pulverization and poor capacity retention during cycling. Therefore, variety of nanostructure group IV elements, including nanoparticles, nanowires, and hollow nanospheres, can be promising solution about the critical issues associated with the large volume change. However, the fundamental research about correlation between the composition and structure for LIB anode is not studied yet. Herein, we successfully synthesized various structure of nanowire such as Si-Ge, Ge-Carbon and Si-graphene core-shell types and analyzed the properties of LIB. Nanowires (NWs) were grown on stainless steel substrates using Au catalyst via VLS (Vapor Liquid Solid) mechanism. And, core-shell NWs were grown by VS (Vapor-Solid) process on the surface of NWs. In order to characterize it, we used FE-SEM, HR-TEM, and Raman spectroscopy. We measured battery property of various nanostructures for checking the capacity and cyclability by cell-tester.

• 대한토목학회논문집
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• 제28권1B호
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• pp.137-147
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• 2008

SVE 공법은 휘발성 유기물로 오염된 불포화대의 정화 공법으로 널리 적용되어 왔다. 본 연구에서는 SVE 적용시 오염물 제거 기작을 관찰하기 위해 모형조 시험을 수행하였으며, 이로부터 SVE의 주요 특징인 tailing 현상, 즉 후반부로 갈수록 제거 속도가 급격히 느려지는 꼬리 효과를 확인하였다. 본 연구에서는 액상 막에서의 확산 제약 현상을 고려할 수 있는 수치 모델을 적용하였으며, 모형조 시험 결과와 구축된 수치 모델링을 통해 SVE의 전형적인 특징이 꼬리 현상을 적절하게 모사할 수 있었다. 또한 4가지 변수에 대한 민감도 분석을 수행하여, 총토양농도의 백분율은 액상확산계수가 클수록, 가스상 확산계수가 클수록, 실제확산경로가 짧을수록, 물포화도가 작을수록 빠르게 감소함을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.382-382
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• 2012

Nanostructures have a larger surface/volume ratio as well as unique mechanical, physical, chemical properties compared to existing bulk materials. Materials for biomedical implants require a good biocompatibility to provide a rapid recovery following surgical procedure and a stabilization of the region where the implants have been inserted. The biocompatibility is evaluated by the degree of the interaction between the implant materials and the cells around the implants. Recent researches on this topic focus on utilizing the characteristics of the nanostructures to improve the biocompatibility. Several studies suggest that the degree of the interaction is varied by the relative size of the nanostructures and cells, and the morphology of the surface of the implant [1, 2]. In this paper, we fabricate the nanowires on the Ti substrate for better biocompatible implants and other biomedical applications such as artificial internal organ, tissue engineered biomaterials, or implantable nano-medical devices. Nanowires are fabricated with two methods: first, nanowire arrays are patterned on the surface using e-beam lithography. Then, the nanowires are further defined with deep reactive ion etching (RIE). The other method is self-assembly based on vapor-liquid-solid (VLS) mechanism using Sn as metal-catalyst. Sn nanoparticle solutions are used in various concentrations to fabricate the nanowires with different pitches. Fabricated nanowries are characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), and high resolution transmission electron microscopy (TEM). Tthe biocompatibility of the nanowires will further be investigated.

• 한국재료학회지
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• 제32권10호
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• pp.435-441
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• 2022

We report the synthesis and gas sensing properties of bare and ZnO decorated TeO₂ nanowires (NWs). A catalyst assisted-vapor-liquid-solid (VLS) growth method was used to synthesize TeO₂ NWs and ZnO decoration was performed using an Au-catalyst assisted-VLS growth method followed by a subsequent heat treatment. Structural and morphological analyses using X-ray diffraction (XRD) and scanning/transmission electron microscopies, respectively, demonstrated the formation of bare and ZnO decorated TeO₂ NWs with desired phase and morphology. NO₂ gas sensing studies were performed at different temperatures ranging from 50 to 400 ℃ towards 50 ppm NO₂ gas. The results obtained showed that both sensors had their best optimal sensing temperature at 350 ℃, while ZnO decorated TeO₂ NWs sensor showed much better sensitivity towards NO₂ relative to a bare TeO₂ NWs gas sensor. The reason for the enhanced sensing performance of the ZnO decorated TeO₂ NWs sensor was attributed to the formation of ZnO (n)/ TeO₂ (p) heterojunctions and the high intrinsic gas sensing properties of ZnO.