• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.286-286
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• 2010

The lack of homogeneously sized single-walled carbon nanotubes (SWNTs) hinders their many applications because properties of SWNTs, in particular electrical conduction, are highly dependent on the diameter and chirality. Therefore, the preferential growth of SWNTs with predetermined diameters is an ultimate objective for applications of SWNTs-based nanoelectronics. It has been previously emphasized that a catalyst size is the one crucial factor to determine the CNTs diameter in chemical vapor deposition (CVD) process, giving rise to several attempts to obtain size-controllable catalyst by diverse methods, such as solid supported catalyst, metal-containing molecular nanoclusters, and nanostructured catalytic layer. In this work, diameter-controlled CNTs were synthesized using a nanostructured catalytic layer consisting of Fe/Al2O3/Si substrate. The CNTs diameter was controlled by structural modification of Al2O3 supporting layer, because Al2O3 supporting layer can affect agglomeration phenomenon induced by heat-driven surface diffusion of Fe catalytic nanoparticles at growth temperature.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.173-179
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• 2018

Electrochemical characterization was conducted on poly(vinyl alcohol) (PVA)-ceramic composite (PVA-CC) separators for supercapacitor applications. The PVA-CC separators were fabricated by mixing various ceramic particles including aluminum oxide ($Al_2O_3$), silicon dioxide ($SiO_2$), and titanium dioxide ($TiO_2$) into a PVA aqueous solution. These ceramic particles help to create amorphous regions in the crystalline structure of the polymer matrix to increase the ionic conductivity of PVA. Supercapacitors were assembled using PVA-CC separators with symmetric activated carbon electrodes and electrochemical characterization showed enhanced specific capacitance, rate capability, cycle life, and ionic conductivity. Supercapacitors using the $PVA-TiO_2$ composite separator showed particularly good electrochemical performance with a 14.4% specific capacitance increase over supercapacitors using the bare PVA separator after 1000 cycles. With regards to safety, PVA becomes plasticized when immersed in 6 M KOH aqueous solution, thus there was no appreciable loss in tear resistance when the ceramic particles were added to PVA. Thus, the enhanced electrochemical properties can be attained without reduction in safety making the addition of ceramic nanoparticles to PVA separators a cost-effective strategy for increasing the ionic conductivity of separator materials for supercapacitor applications.

• Journal of Magnetics
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• v.20 no.3
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• pp.221-228
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• 2015

Colloidal particles consisted of individual nanosized magnetite grains on the surface of the silica cores were obtained by two-stage sol-gel technique. Size distribution and microstructure of the particles were analyzed using atomic force microscopy, X-ray diffraction and Nitrogen thermal desorption. Magnetic properties of the particles were studied by the method of the longitudinal nonlinear response. It has been shown that nanoparticles of magnetite have a size corresponding to a superparamagnetic state but exhibit hysteresis properties. The phenomenon was explained using the magnetostatic interaction model based on the hypothesis of iron oxide particles cluster aggregation on the silica surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.278-278
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• 2010

Electrically tunable photonic band gap (PBG) materials based on crystalline structures have been developed for active components of display. Despite considerable advances, the intrinsic drawbacks of the crystalline PBG materials such as the strong angle dependent hue and difficulty of fabricating defect-free structures in large area have yet to be addressed for their practical applications. Here we report quasi-amorphous colloidal structures exhibiting angle-independent photonic colors in response to the electric stimuli. Moderately polydisperse colloidal Fe3O4@SiO2 nanoparticles dispersed in organic solvents exclusively form quasi-amorphous photonic materials at sufficiently high concentrations (> 30 wt%), and which reversibly reflect incident light in visible region ($\lambda$ peak = 490~655 nm) in response to the relatively low bias voltage (0~4 V). We show the angle-independent tunable photonic colors with the fast response time (50~170 ms) due to the isotropic nature of quasi-amorphous structures. Conventional vacuum injection technique is applicable for fabricating flexible full color photonic display pixels with various pre-defined shapes.

• Korean Chemical Engineering Research
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• v.53 no.3
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• pp.357-363
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• 2015

The development of the environment-friendly tire that meets the standard requirements according to tire labeling system can be improved through using highly homogeneous silica immobilized zinc oxide nanoparticles. In this study, a considerable amount of nanoporous silica was essentially added into nano zinc oxide to improve the physiochemical properties of the formed composite. The introduction of nanoporous silica materials in the composite facilitates the improvement of the wear-resistance and increases the elasticity of the tread. Therefore, the introduction of nanoporous silica can replace carbon black as filler in the formation of composites with desirable properties for conventional green tire. Herein, mesoporous silica immobilized zinc oxide nanoparticle with desirable properties for rubber compounds was investigated. Composites with homogeneous dispersion were obtained in the absence of dispersants. The dispersion stability was controlled through varying the molar ratio, ageing time and mixing order of the reactants. A superior dispersion was achieved in the sample obtained using 0.03 mol of zinc precursor as it had the smallest grain size (50.5 nm) and then immobilized in silica aged for 10 days. Moreover, the specific surface area of this sample was the highest ($649m^2/g$).

• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.473-480
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• 2008

We have investigated the optimal growth conditions of carbon nanotubes (CNTs) using the chemical vapor deposition and the Ni nanoparticle arrays. The diameter of the CNT is shown to be controlled down to below 20 nm by changing the size of Ni particle. The position and size of Ni particles are controlled continuously by using wafer-scale compatible methods such as lithography, ion-milling, and chemical etching. Using optimal growth conditions of temperature, carbon feedstock, and carrier gases, we have demonstrated that an individual CNT can be grown from each Ni nanoparticle with almost 100% probability over wide area of $SiO_2/Si$ wafer. The position, diameter, and wall thickness of the CNT are shown to be controlled by adjusting the growth conditions.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.57-62
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• 2011

We have studied the electrical and magnetic transport properties of tunneling device with FePt magnetic quantum dots. The FePt nanoparticles with a diameter of 8~15 nm were embedded in a $SiO_2$ layer through thermal annealing process at temperature of $800^{\circ}C$ in $N_2$ gas ambient. The electrical properties of the tunneling device were characterized by current-voltage (I-V) measurements under the perpendicular magnetic fields at various temperatures. The nonlinear I-V curves appeared at 20 K, and then it was explained as a conductance blockade by the electron hopping model and tunneling effect through the quantum dots. It was measured also that the negative magneto-resistance ratio increased about 26.2% as increasing external magnetic field up to 9,000 G without regard for an applied electric voltage.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.141-141
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• 2018

Copper is one of the most abundant metals on earth. Its oxide (CuO) is an intrinsically p-type metal-oxide semiconductor with a bandgap ($E_g$) of 1.2-2.0 eV 1. Copper oxide nanomaterials are considered as promising materials for a wide range of applications e.g., lithium ion batteries, dye-sensitized solar cells, photocatalytic hydrogen production, photodetectors, and biogas sensors 2-7. Recently, high-density and uniform CuO nanostructures have been grown on Cu foils in alkaline solutions 3. In 2011, T. Soejima et al. proposed a facile process for the oxidation synthesis of CuO nanobelt arrays using $NH_3-H_2O_2$ aqueous solution 8. In 2017, G. Kaur et al. synthesized CuO nanostructures by treating Cu foils in $NH_4OH$ at room temperature for different treatment times 9. The surface treatment of Cu in alkaline aqueous solutions is a potential method for the mass fabrication of CuO nanostructures with high uniformity and density. It is interesting to compare the gas sensing properties among CuO nanomaterials synthesized by this approach and by others. Nevertheless, none of above studies investigated the gas sensing properties of as-synthesized CuO nanomaterials. In this study, CuO nanowalls versus nanoparticles were synthesized via the oxidation process of Cu foil in NH4OH solution at $50-70^{\circ}C$. The gas sensing properties of the as-prepared CuO nanoplates were examined with $C_2H_5OH$, $CH_3COCH_3$, and $NH_3$ at $200-360^{\circ}C$.

• 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.

• Journal of Environmental Science International
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• v.20 no.2
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• pp.251-260
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• 2011

$TiO_2$- and $SiO_2$-supported $Co_3O_4$, Pt and $Co_3O_4$-Pt catalysts have been studied for CO and $C_3H_8$ oxidations at temperatures less than $250^{\circ}C$ which is a lower limit of light-off temperatures to oxidize them during emission test cycles of gasoline-fueled automotives with TWCs (three-way catalytic converters) consisting mainly of Pt, Pd and Rh. All the catalysts after appropriate activation such as calcination at $350^{\circ}C$ and reduction at $400^{\circ}C$ exhibited significant dependence on both their preparation techniques and supports upon CO oxidation at chosen temperatures. A Pt/$TiO_2$ catalyst prepared by using an ion-exchange method (IE) has much better activity for such CO oxidation because of smaller Pt nanoparticles, compared to a supported Pt obtained via an incipient wetness (IW). Supported $Co_3O_4$-only catalysts are very active for CO oxidation even at $100^{\circ}C$, but the use of $TiO_2$ as a support and the IW technique give the best performances. These effects on supports and preparation methods were indicated for $Co_3O_4$-Pt catalysts. Based on activity profiles of CO oxidation at $100^{\circ}C$ over a physical mixture of supported Pt and $Co_3O_4$ after activation under different conditions, and typical light-off temperatures of CO and unburned hydrocarbons in common TWCs as tested for $C_3H_8$ oxidation at $250^{\circ}C$ with a Pt-exchanged $SiO_2$ catalyst, this study may offer an useful approach to substitute $Co_3O_4$ for a part of platinum group metals, particularly Pt, thereby lowering the usage of the precious metals.