• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.437-443
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• 2010

In recent years, as nano scale structured thin film technology has emerged in various fields such as the materials, biomedical and acoustic sciences, the quantitative nondestructive adhesion evaluation of thin film interfaces using ultra high frequency scanning acoustic microscopy(SAM) has become an important issue in terms of the longevity and durability of thin film devices. In this study, an effective technique for investigating the interfaces of nano scale structured thin film systems is described, based on the focusing of ultrasonic waves, the generation of leaky surface acoustic waves(LSAWs), V(z) curve simulation and ultra high frequency acoustical imaging_ Computer simulations of the V(z) curve were performed to estimate the sensitivity of detection of micro flaws(i.e., delamination) in a thin film system. Finally, experiments were conducted to confirm that a SAM system operating at a frequency of 1 GHz can be useful to visualize the micro flaws in nano structured thin film systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1529-1534
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• 2012

In this study, tensile tests for 12-${\mu}m$-thick copper thin foils were performed by using the DIC method. The DIC method provided precise stress-strain curves for thin film materials, and a commercial inkjet printer can be simply and effectively used for printing speckle patterns on the specimen of Cu thin films whose surface contrast is too low to apply the DIC method. The mechanical properties of Cu thin foils obtained in this study are as follows: elastic modulus E = 89.2 GPa, 0.2% offset yield stress $S_{0.2%}$= 232.8 MPa, tensile strength $S_u$= 319.2 MPa, elongation at fracture ${\varepsilon}_f$=16.8 %, and Poisson's ratio ${\nu}$= 0.34.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.184-188
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• 1999

PbTe thin films of high quality were deposited on HF-treated Si(100) substrates at various substrate temperature by pulsed laser deposition technique. XRD patterns showed that PbTe layers were well-crystallized to a cubic phase with (h00) preferred orientation with the substrate temperature up to $300^{\circ}C$. PbTe films could not form at substrate temperature above $400^{\circ}C$ because of reevaporation of the Pb. According to AFM image, the surface of films was composed of small granular crystals and flat matrix. According to the increase of substrate temperature, the grain size at film surface becomes larger. By Hall-effect measurement, the carrier concentration and Hall mobility of n-type PbTe films grown by $T_{sub}=300^{\circ}C$ were $3.68{\times}10^{18}cm^{-3}$ and $148\;cm^2/Vs$, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.270-270
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• 2011

전이금속(transition metal) 질화물(nitride)은 높은 경도, 내마모성, 부식 저항성 그리고 내열성 등과 같은 우수한 기계적 물성 때문에 많은 연구가 되어 왔다. 이 중 질화 티타늄은 높은 경도, 내식 및 내마모의 우수한 기계적 특성으로 공구(tool)와 같은 제품의 수명 향상을 위한 표면 코팅소재로 사용되어 왔으며, 금(gold)색의 미려한 색상을 이용한 제품의 외관 표면처리와 인체에 무해한 특성을 활용한 정형외과 및 치과용 보형물의 수명 및 안정성 향상 등 다양한 분야에 응용 되고 있다. 본 연구에서는 아크방전을 이용한 경사 코팅법으로 질화 티타늄을 합성하였으며, 경사 코팅에 따른 단층 및 다층 박막(2~3 layer)의 미세조직 변화와 그 물성을 평가하였다. 아크 소스에 장착된 타겟은 120 $mm{\Phi}$, 99.5%의 Ti 타겟을 사용하였고, 시편과 타겟 간의 거리는 약 30 cm이며, 시편은 냉연강판과 SUS를 사용하였다. 시편을 진공용기에 장착하고 ~10-6 Torr까지 진공배기를 실시하고, Ar 가스를 진공용기 내로 공급하여 ~10-4 Torr에서 시편에 bias (Pulse : 400 V)를 인가한 후 아크를 발생시켜 약 5분간 청정을 실시하였다. 플라즈마 청정이 끝나면 시편에 인가된 bias를 차단하고 코팅하였다. 경사 코팅을 위한 시편의 회전각은 45$^{\circ}$, -45$^{\circ}$이며, 질화 티타늄의 두께는 약 3 ${\mu}m$로 동일하게 코팅 하였다. 45$^{\circ}$ 단일층의 경우 0$^{\circ}$ 단일층보다 경도가 감소하나 zigzag 구조의 다층으로 갈수록 45$^{\circ}$ 단일층과 비교하여 확연히 경도가 증가함을 볼 수 있었다. 다층 질화 티타늄의 경사 코팅을 통해 박막의 미세조직 변화를 SEM 이미지를 통해 확인하였으며 증착 방식에 따라 경도, 조도, 반사도 등의 물성 변화가 나타났다. 본 연구에서 얻어진 결과를 이용하여 다양한 형태의 박막구조 제어를 통한 물성변화가 가능할 것으로 예상된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1201-1206
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• 2013

Defects that occur during the manufacturing process or operation of a wind turbine blade have a great influence on its life and safety. Typically, defects such as delamination, pore, wrinkle and matrix crack are found in a blade. In this study, the detectability of the pores, a type of defect that frequently occur during manufacturing, was examined from the full field strain distribution determined with the image correlation technique. Pore defects were artificially introduced in four-ply laminated GFRP composites with $0^{\circ}/{\pm}45^{\circ}$ fiber direction. The artificial pores were introduced in consideration of their size and location. Three different-sized pores with diameter of 1, 2 and 3 mm were located on the top and bottom surface and embedded. By applying static loads of 0-200 MPa, the strain distributions over the specimen with the pore defects were determined using image correlation technique. It was found the pores with diameter exceeding 2 mm can be detected in diameter.

• Journal of IKEEE
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• v.14 no.3
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• pp.219-223
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• 2010

In this study, we fabricated the HgSe nanoparticle-based thin film transistors (TFTs) of back gate structure with PVA gate dielectric. The fabricated TFTs show the improved electrical characteristics in the mobility of $16\;cm^2$/Vs and the on/off ratio of $10^4$ after annealing process at $100^{\circ}C$ for 5 min. AFM images demonstrate that the decrease in surface roughness according to annealing process leads to the improvement of electrical characteristics. The change in drain current caused from the conditions of flexible substrate is investigated under 0.6% strain.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.223.2-223.2
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• 2013

비정질 실리콘은 태양전지, 트랜지스터, 이미지 센서 등 다양한 분야에서 응용되고 있으며 새로운 박막 소자 개발을 위한 소재로서 많은 연구가 진행되고 있다. 하지만 소자개발에 있어 공정상에서 발생하는 비정질 실리콘 박막의 높은 응력(stress)은 소자의 특성을 떨어뜨리는 문제점을 갖는다. 따라서 우수한 특성의 소자 개발을 위해서는 보다 낮은 응력을 갖는 비정질 실리콘 박막 증착 및 공정 조건에 따른 응력 조절이 필요하다. 저응력의 비정질 실리콘 박막 증착은 보다 낮은 반응온도에서 증착속도를 최소로 하여 성장되어야 하는데 이는 플라즈마기상증착(Plasma enhanced chemical vapor deposition, PECVD) 시스템에 의해 가능하다. 따라서 본 연구에서는 PECVD 시스템을 사용하여 비정질 실리콘 박막을 증착하였고 그 특성을 분석하였다. 이 때 증착 온도, rf 파워, 공정 압력은 실험결과로부터 얻어진 낮은 박막 증착속도 하에서 안정적으로 증착이 가능한 조건으로 일정하게 유지하여 실험하였다. 공정 가스는 SiH4/He/N2의 혼합가스를 사용하였고 응력 조절을 위해 SiH4/He 가스비를 일정한 비율로 변화하여 비정질 실리콘 박막을 증착하였다. 증착된 박막의 두께 및 표면 특성은 field emission scanning electron microscopy 및 atomic force microscopy를 이용하여 분석하였고, energy dispersive X-ray 분석을 통하여 정량 및 정성적 분석을 수행하였다. 그리고 stress measurement system을 이용하여 박막의 응력을 측정하였고 X-ray diffraction 측정 및 ellipsometry 측정으로부터 증착된 박막의 결정성, 굴절률 및 oiptical bandgap을 분석하였다.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.3
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• pp.272-279
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• 2017

This study aimed to evaluate the microleakage and penetration of two hydrophilic sealants, Embrace $Wetbond^{TM}$ and Ultraseal $XT^{(R)}$ $hydro^{TM}$, when applied on dry and moist enamel, as compared to a conventionally used hydrophobic sealant, $Clinpro^{TM}$. A total of 60 sound human third molars were randomly divided into 5 groups according to the enamel moisture control and the sealant material used. After sealant application, the teeth were thermocycled and immersed in 1% methylene blue dye. Subsequently, the teeth were sectioned twice and the sections were examined using an optical microscope and image analysis software. Application of Embrace $Wetbond^{TM}$ on either dry or moist enamel resulted in more microleakage than $Clinpro^{TM}$. Application of Ultraseal $XT^{(R)}$ $hydro^{TM}$ on dry enamel showed a similar level of microleakage to $Clinpro^{TM}$, but application on moist enamel resulted in more microleakage. There were no significant differences between the groups in penetration. In conclusion, application of hydrophilic sealants on moist enamel did not improve the sealing ability and showed lower sealing ability than that of $Clinpro^{TM}$ applied on dry enamel.

• Science of Emotion and Sensibility
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• v.23 no.4
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• pp.21-32
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• 2020

The perception of a fashion product may vary depending on the texture and color of its material. Additionally, the product may appear differently in person versus on a digital screen. Therefore, in the present study, we sought to investigate the differences in visual sensibility evaluation between materials in person and on digital screens. In this study, three pairs of visual sensibility adjectives were tested for 60 samples selected as fashion materials. Fashion materials were divided into colors, embossings, and visual clarity categories. Results showed that each color had the same sense during in-person and digital evaluation. In terms of visual sensibility according to embossing, both in-person and digital evaluations of materials with embossings were found to have the same visual sense, whereas those without embossings looked different between in-person and digital evaluations. Assessments based on visual classification showed that both in-person and digital evaluations had the same sensibility. This study is meaningful in suggesting that when evaluating the visual sense of fashion material, the sensation for the digital screen versus in person may be different in some cases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.37-46
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• 2004

Several notes on ground effects drawn from Navier-Stokes analyses and their aerodynamic interpretations were addressed here; For two-dimensional ground effect, the change of surface pressure due to image vortex, the venturi effect due to thickness and the primary inviscid flow phenomena of ground effect, and for three-dimensional ground effect, strengthened wing tip vortices, increased effective span and the outward drift of trailing vortices. Irodov's criteria were evaluated to investigate the static longitudinal stability of conventional NACA 6409 and DHMTU 8-30 airfoils. The analysis results demonstrated superior static longitudinal stability of DHMTU 8-30 airfoil. The DHMTU airfoil has quite lower value of lrodov's criterion than the conventional NACA airfoil, which require much smaller tail volume to stabilize the whole WIG-craft at its design stage.