• Nanomaterials
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• v.12 no.8
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• pp.1354-1365
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• 2022

In this work, a high-density alumina layer with high chemical stability was successfully developed by controlling the hydrolysis of hexafluorosilicate (SiF₆^2-) anions through the addition of various concentrations of sodium citrate (SCi) into the electrolyte of plasma electrolysis (PE). To achieve this aim, the substrate samples were anodized in alkaline aluminate-SiF₆^2--based electrolytes with 0, 5, and 10 g/L of SCi. The presence of SCi anions in the electrolyte led to the formation of a thick adsorbed electrochemical double layer (EDL) on the substrate surface. The EDL not only affected the movement of SiF₆^2- anions towards the anode but also influenced their hydrolysis reaction, which in turn led to a controllable sealing of structural defects with the hydrolysis products, namely SiO₂ and AlF₃. Among three different oxide layers, the oxide layer obtained from the electrolyte with 5 g/L SCi showed the highest chemical stability in a corrosive solution, which was linked to the fact that a considerable increase in the compactness of the oxide layers was obtained by the incorporation of SiO₂ and AlF₃. The mechanism underlying the effects of SCi on triggering the hydrolysis of SiF₆^2- anions and factors affecting chemical stability are discussed based on the experimental data and computational analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.175-175
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• 1999

Circumventing problems lying in the conventional lithographic techniques, we devised a new method for the fabrication of nanometer scale metal wires inspired by the unique characteristics of carbon nanotubes (CNTs). Since carbon nanotubes could act as masks when CNT-coated thin Au/Ti layer on a SiO2 surface was physically etched by low energy argon ion bombardment 9ion milling), Au/Ti nano-wires were successfully formed just below the CNTs exactly duplicating their lateral shapes. Cross-sectional analysis by transmission electron microscopy revealed that the edge of the metal wire was very sharply developed indicating the great difference in the milling rates between the CNTs and the metal layer as well as the good directionality of the ion milling. We could easily find a few nanometer-wide Au/Ti wires among the wires of various width. After the formation of nano-wires, the CNTs could be pushed away from the metal nano-wire by atomic force microscopy, The lateral force for the removal of the CNTs are dependent upon the width and shape of the wires. Resistance of the metal nano-wires without the CNTs was also measured through the micro-contacts definted by electron beam lithography. since this CNT-based lithographic technique is, in principle, applicable to any kinds of materials, it can be very useful in exploring the fields of nano-science and technology, especially when it is combines with the CNT manipulation techniques.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.2
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• pp.126-130
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• 2011

In this study, off-axis magnetron sputtering was used for the crystallized ITO thin films at a low temperature of about $120^{\circ}C$ instead of the conventional RF sputtering because the off-axis sputtering can avoid the damage for the plasma as well as fabrication of thin films with a high quality. The ITO thin films grown on PET substrate at $120^{\circ}C$ were crystallized with a (222) preferred orientation. 58-nm thick ITO films showed a resistivity of about $2{\times}10-4{\Omega}{\cdot}cm$ and a transmittance of about 75% at a wavelength of 550 nm. The transmittance of the ITO thin films by an insertion of SiO2 thin films on ITO films was improved.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.489-490
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• 2006

Branched sulfonated poly(ether sulfone-ketone) copolymer was prepared with bisphenol A, 4,4-difluorobenzophenone, sulfonated chlorophenyl sulfone (40mole% of bisphenol A) and THPE (1,1,1-tris-p-hydroxyphenylethane). THPE was used 0.4 mol% of bisphenol A to synthesize branched copolymers. Organic-inorganic nano composite membranes were prepared with copolymer and a series of $SiO_2$ nanoparticles (20 nm, 4, 7 and 10 wt%). The composite membranes were cast from dimethylsulfoxide solutions. The films were converted from the salt to acid forms with dilute hydrochloric acid. The membranes were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. Branched copolymer and nano composite membranes exhibit proton conductivities from $1.12{\times}10^{-3}$ to $6.04{\times}10^{-3}\;S/cm^2$, water uptake from 52.9 to 62.4%, IEC from 0.81 to 1.21 meq/g and methanol diffusion coefficients from $1.2{\times}10^{-7}$ to $1.5{\times}10^{-7}\;cm^2/S$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.317-318
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• 2012

현재의 반도체 산업에서 Hafnium oxide와 Hafnium silicates같은 high-k 물질은 CMOS gate와 DRAM capacitor dielectrics로 사용하기 위한 대표적인 물질에 속한다. MOSFET (metal oxide semiconductor field effect transistor)구조에서 gate length는 16 nm 이하로 계속 미세화가 연구 중이고, 또한 gate는 기존구조에서 Multi-gate구조로 다변화가 일어나고 있다. 이를 통해 게이트 절연막은 그 구조와 활용범위가 다양해지게 될 것이다. 동시에 leakage current와 dielectric break-down을 감소시키는 연구가 중요해지고 있다. 그러나 나노 영역에서의 기계적 특성에 대한 연구는 전무한 상태이다. 따라서 복잡한 회로 공정, 다양한 Multi-gate 구조, 신뢰도의 향상을 위해서는 유전박막 물질자체와 계면에서의 물리적, 기계적인 특징의 측정이 상당히 중요해지고 있다. 이에 본 연구는 Nano-indenter의 통해 경도(Hardness)와 탄성계수(Elastic modulus) 등의 측정을 통하여 시료 표면의 나노영역에서의 기계적 특성을 연구하고자 하였다. $HfO_2$게이트 절연막은 rf magnetron sputter를 이용해 Si (silicon) (100)기판위에 박막형태로 증착하였고, 이후 furnace에서 질소분위기로 온도(400, 450, $500^{\circ}C$)를 달리하여 20분 열처리를 하였다. 또한 Weibull distribution을 이용해 박막의 characteristic value를 계산하였으며, 실험결과 열처리 온도가 $400^{\circ}C$에서 $500^{\circ}C$로 증가함에 따라 경도와 탄성계수는 7.4 GPa에서 10.65 GPa으로 120.25 GPa에서 137.95 GPa으로 각각 증가하였다. 이는 재료적 측면으로 재료의 구조적 우수성이 증가된 것으로 판단된다.

• Bulletin of the Korean Chemical Society
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• v.24 no.4
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• pp.499-503
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• 2003

Encapsulation of L-ascorbic acid (vitamin C) within a bio-compatible layered inorganic material was achieved by coprecipitation reaction, in which the layered inorganic lattice and its intercalate of vitamin C are simultaneously formed. The nano-meter sized powders of vitamin C intercalate thus prepared was again encapsulated with silica nano-sol to form a nanoporous shell structure. This ternary nanohybrid of vitamin Clayered inorganic core-$SiO_2$ shell exhibited an enhanced storage stability and a sustained releasing of vitamin C. Furthermore, the nano-encapsulation of vitamin C with inorganic mineral was very helpful in delivering vitamin C molecules into skin through stratum corneum, facilitating transdermal penetration of vitamin C in topical application.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.93-97
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• 2012

In this study, the fabrication and the characteristic analyses of OLED using in-situ passivation are investigated. OLEDs represent a disadvantage in decreasing its life due to the degradation caused by the penetration of moisture and oxygen. After the fabrication of OLED, an in-situ passivation method for inorganic thin films is developed. A process that uses PECVD method which can apply a vapor deposition process at room temperature is also developed. Changes in the degradation and electric characteristics of OLEDs are also analyzed by applying $SiO_2$ and SiNx thin films to OLED as a passivation layer. By applying the fabricated thin film to OLEDs as a passivation layer, the moisture penetration in a single layer film is ensured below $1{\times}10^{-2}\;g/m^2.day$. This leads to the improvement of such degradation characteristics in the application of multilayer films.

• Composites Research
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• v.18 no.1
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• pp.23-29
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• 2005

In this work, the effect of ozone treatment of montmorillonite (MMT) on the surface characteristics of montmorillonite and the thermal stability of MMT/polypropylene (PP) nanocomposites was investigated. The surface properties of MMT were determined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). Also, the thermal stability of nanocomposites was investigated in thermogravimetric analysis (TGA). As a result, it was found that the silicate interlayers of the organically modified MMT (D-MMT) were increased by about 11${\AA}$, as compared with the MMT. Also, FT-IR showed that a new peaks at $2800\~2900\;cm^{-1}$ appeared due to the $CH_2$ mode in the D-MMT The ozone treatment of the MMT led to an increase of SiO or $SiO_2$ groups on MMT surfaces, resulting in increasing the oxygen-containing functional groups on MMT. The ozonized MMT had higher thermal stability than that of untreated nanocomposites. This was due to the improvement of interfacial bonding strengths, resulting from the acid-base interfacial interactions between PP and MMT.

• Journal of Powder Materials
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• v.25 no.1
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• pp.12-18
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• 2018

Cost-effective functional phosphor nanoparticles are prepared by introducing low-cost $SiO_2$ spheres to rare-earth phosphor ($YVO_4:Eu^{3+}$, $YVO_4:Er^{3+}$, and $YVO_4:Nd^{3+}$) shells using a sol-gel synthetic method. These functional nanoparticles are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and general photoluminescence spectra. The $SiO_2$ sphere occupying the interior of the conventional phosphor is advantageous in significantly reducing the cost of expensive rare-earth phosphor nanoparticles. The sol-gel process facilitates the core-shell structure formation; the rare-earth shell phosphor has strong interactions with chelating agents on the surfaces of $SiO_2$ nanoparticles and thus forms layers of several nanometers in thickness. The photoluminescence wavelength is simply tuned by replacing the active materials of $Eu^{3+}$, $Er^{3+}$, and $Nd^{3+}$. Moreover, the photoluminescent properties of the core-shell nanoparticles can be optimized by manipulating the specific contents of active materials in the phosphors. Our simple approach substitutes low-cost $SiO_2$ for expensive rare-earth-based phosphor materials to realize cost-effective phosphor nanoparticles for various applications.

• Computers and Concrete
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• v.21 no.6
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.