• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.139-142
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• 2018

Silicon (Si) is a promising anode material for next-generation lithium ion batteries (LIBs) because of its high capacity of 4,200 mAh/g ($Li_{4.4}Si$ phase). However, the large volume expansion of Si during lithiation leads to electrical failure of electrode and rapid capacity decrease. Generally, a binder is homogeneously mixed with active materials to maintain electrical contact, so that Si needs a particular binding system due to its large volume expansion. Polyvinyl alcohol (PVA) is known to form a hydrogen bond with partially hydrolyzed silicon oxide layer on Si nanoparticles. However, the decrease of its cohesiveness followed by the repeated volume change of Si still remains unsolved. To overcome this problem, we have introduced the electrospinning method to weave active materials in a stable nanofibrous PVA structure, where stresses from the large volume change of Si can be contained. We have confirmed that the capacity retention of Si-based LIBs using electrospun PVA matrix is higher compared to the conservative method (only dissolving in the slurry); the $25^{th}$ cycle capacity retention ratio based on the $2^{nd}$ cycle was 37% for the electrode with electrospun PVA matrix, compared to 27% and 8% for the electrodes with PVdF and PVA binders.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.447-447
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• 2013

최근 전자산업의 발전으로 차세대 디스플레이 소자로 산화물반도체가 주목받고 있다. 산화물 반도체는 저온공정, 높은 이동도 및 투과율을 가지기 때문에 이러한 공정이나 물성 측면에 있어 기존의 a-Si, LTPS 등을 대채할 만한 소자로서 연구가 활발이 이루어지고 있다. 특히 고해상도 및 고속구동이 진행됨에 따라 높은 이동도의 필요성이 대두되고 있다. 본 연구에서는 IGZO 산화물 반도체 박막트랜지스터의 이동도 개선을 위해 나노입자를 사용하였다. 게이트전극으로 사용된 Heaviliy doped P-type Si 기판위에 200 nm의 SiO2 절연층을 성장시킨 후, 채널로 작동하기 위한 IGZO 박막을 증착하기 전에 10~20 nm 크기의 니켈, 금 나노입자를 부착시켰다. 열처리 온도는 $350^{\circ}C$, 90분동안 진행하였고, 100 nm의 알루미늄 전극을 증착시켜 TFT 소자를 제작하였다. TFT 소자가 동작할 시, IGZO 박막 내부의 전자들은 게이트 전압으로 인해 하부로 이동하여 채널을 형성, 동시에 드레인 전압으로 인한 캐리어들의 움직임으로 인해 소자가 동작하게 된다. 본 연구에서는 채널이 형성되는 계면 부근에 전도성이 높은 금속 나노입자를 부착시켜 다수 캐리어인 전자가 채널을 통과할 때 전류흐름에 금속 나노입자들이 기여하여 전기적 특성의 변화에 어떠한 영향을 주는지 연구하였다. 반응시간을 조절하여 기판에 붙는 나노입자의 밀도 변화에 따른 특성과 다양한 크기(5, 10, 20 nm)를 갖는 금, 니켈 나노입자를 포함한 IGZO TFTs 소자를 제작하여 전달특성, 출력특성의 변화를 비교하였고, 실질적인 채널길이의 감소효율과 캐리어 이동도의 변화를 비교분석 하였다.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3723-3729
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• 2010

We investigated the high-excitation voltage cathodoluminescence (CL) performance of blue light-emitting (ZnS:Ag,Al,Cl) and green light-emitting (ZnS:Cu,Al) phosphors coated with metal oxides ($SiO_2$, $Al_2O_3$, and MgO). Hydrolysis of the metal oxide precursors tetraethoxysilane, aluminum isopropoxide, and magnesium nitrate, with subsequent heat annealing at $400^{\circ}C$, produced $SiO_2$ nanoparticles, an $Al_2O_3$ thin film, and MgO scale-type film, respectively, on the surface of the phosphors. Effects of the phosphor surface coatings on CL intensities and aging behavior of the phosphors were assessed using an accelerating voltage of 12 kV. The MgO thick film coverage exhibited less reduction in initial CL intensity and was most effective in improving aging degradation. Phosphors treated with a low concentration of magnesium nitrate maintained their initial CL intensities without aging degradation for 2000 s. In contrast, the $SiO_2$ and the $Al_2O_3$ coverages were ineffective in improving aging degradation.

• Nuclear Engineering and Technology
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• v.44 no.4
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• pp.429-436
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• 2012

Critical heat flux (CHF) is the thermal limit of a phenomenon in which a phase change occurs during heating (such as bubbles forming on a metal surface used to heat water), which suddenly decreases the heat transfer efficiency, thus causing localized overheating of the heating surface. The enhancement of CHF can increase the safety margins and allow operation at higher heat fluxes; thus, it can increase the economy. A very interesting characteristic of nanofluids is their ability to significantly enhance the CHF. Nanofluids are nanotechnology-based colloidal dispersions engineered through the stable suspension of nanoparticles. All experiments were performed in round tubes with an inner diameter of 0.01041 m and a length of 0.5 m under low pressure and low flow (LPLF) conditions at a fixed inlet temperature using water, 0.01 vol.% $Al_2O_3$/water nanofluid, and SiC/water nanofluid. It was found that the CHF of the nanofluids was enhanced and the CHF of the SiC/water nanofluid was more enhanced than that of the $Al_2O_3$/water nanofluid.

• Journal of the Korean Institute of Gas
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• v.26 no.2
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• pp.1-8
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• 2022

The purpose of this study is to prepare GPTMS((3-Glycidoxypropyl) trimethoxysilane)-SiO₂ nanofluid and analyze the effect of nanofluid injection on carbonate reservoirs. Structural analysis of silica nanoparticles modified by GPTMS was investigated by FTIR(Fourier transform infrared spectroscopy). C-H stretching vibrations at 2,950 cm^-1 indicating the silica surface modification with GPTMS were observed when the silane feed was over 0.5 mmol/g. Also, the coreflooding test by nanofluid injection on the aged limestone and dolomite plug samples was carried out with different particle concentration and flow rate. The incremental oil recovery was up to 18.9%, and contact angle and permeability of carbonate samples were changed by the effect of nanoparticle adsorption on pore which caused wettability alteration and pore size change. Therefore, the prepared nanofluid will be utilized as an injection fluid for enhancing oil recovery and modifying fluid flow properties such as change of rock wettability and permeability in carbonate reservoirs.

• Polymer(Korea)
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• v.36 no.3
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• pp.372-379
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• 2012

In this study, we treated silica nanoparticles with bis[3-(trimethoxysilyl)propyl]amine (BTMA) silane coupling agent to modify their surfaces. We investigated the effects of BTMA hydrolysis time, BTMA concentration and BTMA treatment time on the degree of silanization reaction of silica nanoparticles. We used Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and solid state cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance spectroscopy (NMR) to obtain quantitative data. We found the decrease of isolated Si-OH peak intensity at 3747 $cm^{-1}$ and the increase of $-CH_2 $stretching and bending peaks with increasing hydrolysis time, concentration and treatment time of BTMA. EA analysis results also supported this trend. We found a strong effect of BTMA concentration on the degree of silanization of the silica particles, but weak effects of the hydrolysis time and the treatment time.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1202-1207
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• 2003

Using a recently developed Hybric Plasma-Particle Accelerating Impact Deposition (HP-PAID) process, synthesis of nanostructured silicon coatings has been investigated by injecting vapor-phase TEOS (tetraethosysilane, (C$_2$H$\_$5/O)$_4$Si) into an Ar hybrid plasma. The plasma jet with reactants was expanded through nozzle into a deposition chamber, with the pressure dropping from 700 to 10 torr. Ultrafine particles accelerated in the free jet downstream of the nozzle, deposited by an inertial impaction onto a temperature controlled substrate. By using this process, nanostructured amorphous silicon coatings with grain size smaller than 10 nm could be synthesized. These samples were annealed in an Ar and crystallized at 900$^{\circ}C$ for 30 min. TEM analysis showed that the annealed coatings were also composed of nanoparticles smaller than 10 nm, which showed a good consistency that the average grain size of 7 nm was also estimated from a peak shift of 2.39 cm$\^$-1/ and Full Width at Half Maximum (FWHM) 5.92 cm$\^$-1/ of Raman analysis. The noteworthy is that a strong PL peak at 398 nm was also obtained for this sample, which indicates that the deposited coatings also contained 3∼4 nm nanostructured grains.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.3
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• pp.9-17
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• 2011

Nano-composite solders have been studied to improve the properties of Pb-free solder joints. The nanoparticles in the composite solders were carbon nanotubes(CNTs), metals (Ag, Ni, Cr, etc.), ceramics (SiC, $ZrO_2$, $TiB_2$, etc.). To fabricate the nano-composite solders, mechanical mixing methods and in-situ fabrication method has been used for well-dispersed nano phase. The characteristic properties of the nano-composite solders were high creep resistance, low undercooling, low IMC growth rate and fine microstructures. More researches on the nano-composite solders are required to improve the processibility and the reliability of the nano-composite solder joints.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.411-417
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• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.

• Polymer(Korea)
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• v.37 no.3
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• pp.308-315
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• 2013

In this study, we performed surface modification of silica nanoparticles with bis[3-(triethoxysilylpropyl)]tetrasulfide (TESPT) silane coupling agent to study the effects of treatment temperature, treatment time, and amount of TESPT used on the silanization degree with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), elemental analysis (EA) and solid state $^{13}C$ and $^{29}Si$ cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance spectroscopy (NMR). We found peak area of isolated silanol groups at $3747cm^{-1}$ decreased, but peak area of $-CH_2$ asymmetric stretching of TESPT at $2938cm^{-1}$ increased with the amount of TESPT from FTIR measurements. We also used universal testing machine (UTM) to study mechanical properties of styrene butadiene rubber (SBR) nanocomposites with 20 phr (parts per hundred of rubber) of pristine and TESPT modified silicas, respectively. The tensile strength and 100% modulus of modified silica/SBR nanocomposite were enhanced from 5.65 to 9.38MPa, from 1.62 to 2.73 MPa, respectively, compared to those of pristine silica/SBR nanocomposite.