• 한국전기전자재료학회논문지
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• 제24권2호
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• pp.152-155
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• 2011

Even though nano-scale materials were very advantageous for various applications, there are still problems to be solved such as the stabilization of surface state and realization of low contact resistances between a semiconducting nanowire and electrodes in nano-electronics. It is well known that the effects of contacts barrier between nano-channel and metal electrodes were dominant in carrier transportation in individual nano-electronics. In this report, it was investigated the electrical properties of GaN nanorod devices after chemical etching and rapid thermal annealing for making good contacts. After KOH wet-etching of the contact area the devices showed better electrical performance compared with non-treated GaN individual devices but still didn't have linear voltage-current characteristics. The shape of voltage-current properties of GaN devices were improved remarkably after rapid thermal annealing as showing Ohmic behaviors with further bigger conductivities. Even though chemical etching of the nanorod surfaces could cause scattering of carriers, in here it was shown that the most important and dominant factor in carrier transport of nano-electronics was realization of low contact barrier between nano-channel and metal electrodes surely.

• 열처리공학회지
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• 제20권2호
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• pp.65-71
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• 2007

Microstructural changes and hardness variations in STS 304 steel have been investigated during the processes of carbide dispersion (CD) carburization; carburization, austenitization, subzero treatment and tempering. The carbon content of the surface layer increased up to maximum 4.0% after carburization, and the content was homogenized with the value of 2.3% to the $95{\mu}m$ from the surface after austenitization. The carbide appeared during CD carburization process was $Cr_7C_3$ type, which was composed network carbides along the austenite grain boundaries, square type carbides in the interior of the grain and fine nano-sized carbides. The fine nano-sized carbides precipitated at the austenitization stage and possibly subzero treatment stage were coarsened after tempering at $200^{\circ}C$, resulting the hardness decrease. The tempered steel without subzero treatment increased hardness with increasing time due to the continuous precipitation of fine carbides during tempering. The nano-sized carbide appeared square type morphology.

• 센서학회지
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• 제15권5호
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• pp.371-377
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• 2006

Nano porous, transparent silica aerogels monoliths were prepared under ambient drying (1 atm, $270^{\circ}C$) condition by the combination of sol-gel process and surface modification with subsequent heat treatment. Three kinds of solvent, n-hexane, n-heptane and xylene, were selected in the point view of low surface tension and vapor pressure in order to restrain a formation of cracks during drying. Crack-free silica aerogels with over 93 % of porosity and below $0.14g/cm^3$ of density were obtained by solvent exchange and surface modification under atmosphere condition. Optimum solvent was confirmed n-heptane among these solvents through estimation of FT-IR, TGA, BET and SEM. Modified silica aerogel exhibited a higher porosity and pore size compare to unmodified aerogels. Hydrophobicity was also controled by C-H and H-OH bonding state in the gel structure and heat treatment over $400^{\circ}C$ effects to the hydrophobicity due to oxidation of C-H radicals.

• 한국전기전자재료학회논문지
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• 제24권10호
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• pp.790-793
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• 2011

In this study, the surface modification for a silicon(Si) mold using $CHF_3$ inductively coupled plasma(ICP). The conditions under that plasma was treated a input ICP power 600 W, an operating gas pressure of 10 mTorr and plasma exposure time of 30 sec. The Si mold surface became hydrophobic after plasma treatment in order to $CF_x$(X= 1,2,3) polymer. However, as the de-molding process repeated, it was investigated that the contact angle of Si surface was decreased. So, we attempted to investigate the degradation mechanism of the accurate pattern transfer with increasing the count of the de-molding process using scanning electron microscope (SEM), contact angle, and x-ray photoelectron spectroscopy (XPS) analysis of Si mold surface.

• Corrosion Science and Technology
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• 제18권5호
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• pp.196-205
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• 2019

Surface modification techniques are known to improve SCC by adding large compressive residual stresses to metal surfaces. This surface modification technology is attracting attention because it is an economical and practical technology compared to the maintenance method of existing nuclear power plants. Surface modification techniques include laser, water jet and ultrasonic peening, pinning and ultrasonic Nano-crystal surface modification (UNSM). The focus of this study was on the effect of ultrasonic amplitude in UNSM treatment on the corrosion properties of Alloy 600. A microstructure analysis was conducted using an optical microscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). A cyclic polarization test and AC-impedance measurement were both used to analyze the corrosion properties. UNSM treatment influences the corrosion resistance of Alloy 600 depending on its amplitude. Below the critical amplitude value, the pitting corrosion properties are improved by grain refinement and compressive residual stress, but above the critical amplitude value, crevices are formed by the formation of overlapped waves. These crevices act as corrosion initiators, reducing pitting corrosion resistance.

• 한국재료학회지
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• 제17권10호
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• pp.544-547
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• 2007

Human teeth were scratched by the abrasive paper, dropping in hydroxyapatite solution during 1, 2, 3, 4 months. We studied teeth surface change with SEM each months. After 1 months treatment the surface appeared the change. Because of the hydroxyapatite ion exchange mechanism. The scratched surface was recovered by the hydroxyapatite. The results of EDS showed that $Ca^{2+}$ ion and $PO_4^{3-}$ ion were removed from hydroxyapatite solution to scratched teeth surface.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.33.2-33.2
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• 2009

Block copolymer lithography has attracted great attention for emerging nanolithography since nanoscaleperiodic patterns can be easily obtained through self-assembly process without conventional top-down patterning process. Since the morphologies of self-assembled block copolymer patterns are strongly dependent on surface energy of a substrate, suitable surface modification is required. Until now, the surface modification has been studied by using random copolymer or self-assembled mono layers (SAMs). However, the research on surface modifications has been limited within several substrates such as Si-based materials. In present study, we investigated the formation of block copolymer on Au substrate by $O_2$ plasma treatment with the SAM of 3-(p-methoxy-phenyl)propyltrichloro-silane [MPTS, $CH_3OPh(CH_2)_3SiCl_3$]. After $O_2$ plasma treatment, the chemical bonding states of the surface were analyzed by X-ray photoelectron spectroscopy (XPS). The static contact angle measurement was performed to study the effects of $O_2$ plasma treatment on the formation of MPTS monolayer. The block copolymer nanotemplates formed on Au surface were analyzed by scanning electron microscopy. The results showed that the ordering of self-assembled block copolymer pattern and the formation of cylindrical nano hole arrays were enhanced dramatically by oxygen plasma treatment. Thus, the oxidation of gold surface by $O_2$ plasma treatment enables the MPTS to form the monolayer assembly leading to surface neutralization of gold substrates.

• 열처리공학회지
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• 제19권2호
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• pp.103-108
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• 2006

Microstructural evolution of Pt-aluminide coated Ni-based superalloy has been investigated with ductilization heat treatment. The Pt coat was prepared on the superalloy and then aluminide coating was conducted using a pack cementation process. Samples were heat-treated at $1050^{\circ}C$ for 2 hrs and the microstructure and element analysis were preformed. A various precipitated compounds were observed within the coating layer and the diffusion region in the Pt-aluminide coating and heat treatment, indicating that the bi-phase compounds of $PtAl_2$ and NiAl were performed during the Pt-aluminide coating, whereas $M_{23}C_6$, MC, $Ni_3Al$ and ${\sigma}$ phases were precipitated in the inter-diffusion region. The bi-phase compounds of $PtAl_2$ and NiAl were transformed into the single phase compound of $PtAl_2$ with the heat treatment, increasing the amount of carbide and ${\sigma}$ phase.

• Journal of Welding and Joining
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• 제33권2호
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• pp.40-46
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• 2015

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

• 한국표면공학회지
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• 제50권3호
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• pp.212-218
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• 2017

$Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrite powders were prepared by self-propagating high temperature synthesis followed by classifying with an ultrasonic wet-magnetic separation unit to get high pure nano-sized particles. The $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrites were well formed by using several powders like iron, nickel oxide, zinc oxide and magnesium oxide at 0.1 MPa of oxygen pressure. The ultrasonic wet-magnetic separation of pre-mechanical milled ferrite powders resulted in producing the powders with average size of 800 nm. The addition of a surfactant during the wet-magnetic separation process improved productivity more than twice. The coercive force, maximum magnetization and residual magnetization of the $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ nano-powders with 800 nm size were 3651 A/m, $53.92Am^2/kg$ and $4.0Am^2/kg$, respectively.