• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3629-3633
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• 2011

The effect of a dense $TiO_2$ blocking layer prepared using the sol-gel method on the performance of dye-sensitized solar cells was studied. The blocking layer formed directly on the working electrode, separated it from the electrolyte, and prevented the back transfer of electrons from the electrode to the electrolyte. The dyesensitized solar cells were prepared with a working electrode of fluorine-doped tin oxide glass coated with a blocking layer of dense $TiO_2$, a dye-attached mesoporous $TiO_2$ film, and a nano-gel electrolyte, and a counter electrode of Pt-deposited FTO glass. The gel processing conditions and heat treatment temperature for blocking layer formation affected the morphology and performance of the cells, and their optimal values were determined. The introduction of the blocking layer increased the conversion efficiency of the cell by 7.37% for the cell without a blocking layer to 8.55% for the cell with a dense $TiO_2$ blocking layer, under standard illumination conditions. The short-circuit current density ($J_{sc}$) and open-circuit voltage ($V_{oc}$) also were increased by the addition of a dense $TiO_2$ blocking layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.37-42
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• 2012

LIFT (laser-induced forward transfer) is an advanced laser processing method used for selectively transferring micron-sized objects. In our study, this process was applied in order to deposit solder balls in microsystem packaging processes for electronics. Locally melted solder paste could be transferred to a rigid substrate using laser pulses. A thin glass plate with a solder cream layer was used as a donor film, and an IR laser pulse (wavelength = 1070 nm) was used to transfer a micron-sized solder ball to the receptor. Mass balance and energy balance were applied to analyze the shape and temperature profiles of the solder paste drops. The transferred solder bumps had measured diameters of 30-40 ${\mu}m$ and thicknesses of 50 ${\mu}m$ in our experiment. The limits and applications of this method are also presented.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.5
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• pp.175-180
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• 2016

ZnO nanoparticles were synthesized by aqueous preparation routes of a precipitation and a hydrothermal process. In the processes, the powders were formed by mixing aqueous solutions of Zn-nitrate hexahydrate ($Zn(NO_3)_2{\cdot}6H_2O$) with NaOH aqueous solution under controlled reaction conditions such as Zn precursor concentration, reaction pH and temperature. Single ZnO phase has been obtained under low Zn precursor concentration, high reaction pH and high temperature. The synthesized particles exhibited flakes (plates), multipods or rods morphologies and the crystallite sizes and shapes would be efficiently controllable by changing the processing parameters. The hydrothermal method showed advantageous features over the precipitation process, allowing the precipitates of single ZnO phase with higher crystallinity at relatively low temperatures below $100^{\circ}C$ under a wider pH range for the Zn precursor concentration of 0.1~1 M.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.618-622
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• 2009

The new candidates for OTFTs, which were composed of naphthalene, anthracene, benzo[1,2-b:4,5-b’]dithiophene and 2-decylbithiophene end-capper were synthesized under Suzuki coupling reaction conditions. All of the oligomers were characterized by FT-IR, mass analysis, UV-vis, PL spectrum, cyclic voltametry (CV), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), $^1H-NMR\;and\;^{13}C-NMR$. Investigation of physical properties showed that all of the oligomers have higher oxidation potential and good thermal stability. Especially, DBT-DtB-DBT is soluble in common solvents and suitable for low cost processing technologies.

• Journal of Powder Materials
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• v.15 no.2
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• pp.95-100
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• 2008

The investigation is to modify the mechanical and chemical properties of Mg alloys using a combination of rapid solidification and surface treatment. As the first approach, $Mg_{95}Zn_{4.3}Y_{0.7}$ was gas atomized and pressure sintered by spark plasma sintering process (SPS), showing much finer microstructure and higher strength than the alloys as cast. Further modification was performed by treating the surface of PM Mg specimen using Plasma electrolytic oxidation (PEO) process. During the PEO processing, MgO layer was initiated to form on the surface of Mg powder compacts, and the thickness and the density of MgO layer were varied with the reaction time. The thickening rate became low with the reaction time due to the limited diffusion rate of Mg ions. The surface morphology, corrosion behavior and wear resistance were also discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.99-100
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• 2006

Silicon-on-insulator(SOI) MOSFET with SiGe/Si heterostructure channel is an attractive device due to its potent use for relaxing several limits of CMOS scaling, as well as because of high electron and hole mobility and low power dissipation operation and compatibility with Si CMOS standard processing. SOI technology is known as a possible solution for the problems of premature drain breakdown, hot carrier effects, and threshold voltage roll-off issues in sub-deca nano-scale devices. For the forthcoming generations, the combination of SiGe heterostructures and SOI can be the optimum structure, so that we have developed SOI n-MOSFETs with SiGe/Si heterostructure channel grown by reduced pressure chemical vapor deposition. The SOI n-MOSFETs with a SiGe/Si heterostructure are presented and their DC characteristics are discussed in terms of device structure and fabrication technology.

• Korean Journal of Materials Research
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• v.22 no.7
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• pp.335-341
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• 2012

Recently, the demand for the miniaturization of printed circuit boards has been increasing, as electronic devices have been sharply downsized. Conventional multi-layered PCBs are limited in terms their use with higher packaging densities. Therefore, a build-up process has been adopted as a new multi-layered PCB manufacturing process. In this process, via-holes are used to connect each conductive layer. After the connection of the interlayers created by electro copper plating, the via-holes are filled with a conductive paste. In this study, a desmear treatment, electroless plating and electroplating were carried out to investigate the optimum processing conditions for Cu via filling on a PCB. The desmear treatment involved swelling, etching, reduction, and an acid dip. A seed layer was formed on the via surface by electroless Cu plating. For Cu via filling, the electroplating of Cu from an acid sulfate bath containing typical additives such as PEG(polyethylene glycol), chloride ions, bis-(3-sodiumsulfopropyl disulfide) (SPS), and Janus Green B(JGB) was carried out. The desmear treatment clearly removes laser drilling residue and improves the surface roughness, which is necessary to ensure good adhesion of the Cu. A homogeneous and thick Cu seed layer was deposited on the samples after the desmear treatment. The 2,2'-Dipyridyl additive significantly improves the seed layer quality. SPS, PEG, and JGB additives are necessary to ensure defect-free bottom-up super filling.

• Journal of the Korean institute of surface engineering
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• v.47 no.6
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• pp.316-322
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• 2014

With increase in demand for higher operating temperatures of gas turbines, extensive research efforts have been carried out to enhance the performance of thermal barrier coatings (TBCs) in the field of coating processing as well as materials. In this study, thermal barrier coatings in lanthanum/gadolinium zirconate system, which is one of the most promising candidates for replacing yttira-stabilized zirconia (YSZ) in thermal barrier coating applications, are fabricated via suspension plasma spray. Dense, $300{\sim}400{\mu}m$ thick coatings of fluoritephase zirconate with modest amount of segmented microstructures are obtained by using suspension plasma spray with suspensions of planetary-milled mixture between lanthanum and/or gadolinium oxide and nano zirconia. These coatings exhibit thermal conductivities of 1.6 ~ 1.7 W/mK at $1000^{\circ}C$, which is relatively lower than that of YSZ.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.185-192
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• 2011

The technique of producing thin film plays a crucial role in modern science and technology as well as in industrial purposes. Numerous efforts have been made to get high quality thin film through surface treatment of materials. PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) are two of the most popular deposition techniques used in both scientific study and industrial use. It is well known that the film deposited by PVD and CVD commonly possesses a columnar microstructure which affects many film properties. In recent years, various types of deposition sources which feature high material uses and excellent film properties have been developed. Electromagnetic levitation source appeared as an alternative deposition source to realize high deposition rate for industrial use. Complex film structures such as nano multilayer and multi-components have been prepared to achieve better film properties. Glancing angle deposition (GLAD) has also been developed as a technique to engineer the columnar structure of thin films on the micro- and nanoscale. In this paper, the trends and major issues of thin film technology based on PVD and CVD have been discussed together with the prospect of thin film technology.

• Journal of Food Hygiene and Safety
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• v.34 no.4
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• pp.317-324
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• 2019

This study focuses on the role of nanotechnology in the field of food industries. Bioactive components with antimicrobial activity against food pathogens are encapsulated into nanoparticles (NPs) to improve and extend their efficiency in food preservation. However, these NPs should be biocompatible and nontoxic for humans. Advancement in this field has resulted in the development of NPs for food packaging in some industries. The most commonly used group of NPs in the food industry is metal oxide. As metal oxide NPs such as zinc oxide and titanium dioxide exhibit antimicrobial activity in food materials, the NPs can be used for food preservation with enhanced functional properties. The application and effects of nanotechnology in correlation with the nutritional and sensory properties of foods were briefly discussed with a few insights into safety regulations on nano-based food formulation and preservation.