• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• 터널과지하공간
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• 제20권6호
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• pp.434-445
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• 2010

대용량 전력에너지저장시설로서의 복공식 압축공기 지하저장시설의 기밀시스템을 구성하는 콘크리트 라이닝 및 현장 타설 과정에서 발생하는 시공이음부의 투기특성을 파악하고자 콘크리트 블록시료를 이용한 모형실험을 수행하였다. 시공이음부의 투과계수는 콘크리트 블록보다 약 $10^1{\sim}10^4$ 배 정도의 투과성이 큰 것으로 파악되어, 현장 타설과정에서 시공이음부의 품질관리가 저장시설의 기밀성능 확보 관점에서 매우 중요함을 확인하였다. 또한, 접합면에 아크릴계 접착제를 타설함으로써 시공이음부의 투과계수를 콘크리트 블록 수준까지 감소시킬 수 있었으며 콘크리트 블록의 초기 수분함량이 높을수록 투과계수가 감소하여 기밀성능을 향상시킬 수 있음을 확인하였다.

• 한국기계가공학회지
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• 제18권2호
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• pp.1-6
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• 2019

With the increase in number of the athletic population and elderly demographic, the demand for orthopedic splints, which are used to support a damaged body, has rapidly increased. Current splints mainly consist of inner and outer parts, which are multiple fabrics covered with polyurethane and nonwoven fabrics, respectively. However, the laminated materials with directly applied pre-polymer coating lead to a high defect rate because of the uneven thickness on the surface. Thus, this study proposes an indirect coating method using a precise clearance controller, which enables the even application of the coating material on multiple inner parts while maintaining a constant thickness. In addition, a roll-to-roll (R2R) technique is applied instead of the sewing mechanism to bond the inner and outer materials together and enhance the productivity in the final stage. In the advanced methods, there is a storage tank that contains polyurethane, a clearance controller, and pairs of rollers in the upper and lower rows. To improve the quality of the products and optimize the equipment, three controllable factors are determined: the viscosity of polyurethane, angle of the gap controller and number of pairs of rollers in the R2R system.

• Journal of the Korean Wood Science and Technology
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• 제49권1호
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• pp.57-66
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• 2021

In recent years, the use of cross laminated timber (CLT) has been evolving. In addition, CLT manufactured with various species such as Japanese cedar has been developed to utilize the local resources in each country. However most factories in Japan produce CLT by bonding the laminae in width direction for orthogonal layers, where grain of element is perpendicular to the grain of outer layer, and this process is considered to be one of the factors that reduce productivity. A new wood based material (hereinafter referred to as Ply-lam) using wooden panel such as plywood for the orthogonal layer was developed in order to improve productivity in CLT manufacturing and improve quality. Japanese cypress lamina was used for the parallel layer, where grain of element is parallel to the grain of outer layer, of CLT and Korean larch plywood was used for the orthogonal layer, in order to effectively use Korean larch and expand the utilization of Japanese cypress. The cross-sectional construction of the Ply-lam was 5-layers 5-plies, and the dimensions were 1000 mm (width) × 150 mm (depth) × 4000 mm (length). As a performance evaluation of the manufactured Ply-lam, strength tests such as out-of-plane bending, in-plane bending, out-of-plane shearing and in-plane shearing tests were carried out. As the result of this study, Ply-lam composed of Japanese cypress lamina panels and Korean larch plywood showed very higher out-of-plane bending strength compared to the standard strength of CLT. And the result obtained in other tests seems to show a sufficiently high value.

• 한국기계가공학회지
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• 제19권10호
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• pp.98-104
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• 2020

Recently, friction stir welding of dissimilar materials has become one of the biggest issues in lightweight and eco-friendly bonding technology. In this study, a lightweight torsion beam axle, which is an automobile chassis component, was used in the welding to cast aluminum material. The friction stir welding process of A357 cast aluminum and FB590 high-strength steel as well as the effects of the process parameters were investigated and optimized using a novel definitive screening design (DSD). ANOVA was used to predict the importance of the process parameters with 13 degradation experiments using the proposed DSD. Also, FSWed experiments were conducted using an optical microscope analysis to investigate the tensile strength behavior in the weld area. In addition to determining the interaction between the tool's rotational speed and the plunge speed, results indicate that the influence of the plunge depth was the most significant.

• 접착 및 계면
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• 제24권1호
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• pp.36-40
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• 2023

반데르발스 물질이란 층간 결합이 약한 반데르발스 결합으로 이루어진 이차원 층상구조를 지닌 물질을 의미하며, 이러한 반데르발스 이차원 소재를 이용한 이종접합 구조 연구는 그래핀이 발견된 이후 꾸준히 연구되고 있다. 본 논문에서는 대기압 화학기상증착법을 통해 성장된 단층 단결정 MoSe₂를 기반으로하는 반데르발스 이종접합 트랜지스터 소자에 대해 보고한다. 최적화된 공정조건에서 성장된 MoSe₂는 원자수준의 결함이 존재하지 않는 것을 밝혔으며, 이를 이용한 트랜지스터 소자 또한 우수한 특성을 보인다는 것을 밝혀내었다.

• 열처리공학회지
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• 제36권5호
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• pp.270-276
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• 2023

In this study, we analyzed two types of cold forging dies commonly used for manufacturing general nuts and screws to investigate the differences in WC powder according to the lifespan. For both Type I and Type II dies, it was observed that as the lifespan of the molds increases, the area fraction of Co becomes larger and the size of the powder becomes smaller. Moreover, there is a trend where the strength also increases as the lifespan gets longer. Actually, the hardness value of the sample with the longest lifespan is ~ 131 HV higher than the specimen of the shortest lifespan, It is noted that the reduction in toughness of the WC-Co mold is caused by insufficient Co and the decrease in contact surface area of WC-Co results in a reduced bonding surface area. The lifespan of cold-working WC molds increases when the W content and the volume fraction of WC are high, and the size of the WC powder is small. The results can significantly enhance producing high-quality molds with an extended lifespan using WC powder for cold forging.

• 항공우주시스템공학회지
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• 제16권1호
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• pp.12-16
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• 2022

유도 용접은 비접촉식으로 깨끗하고 빠른 공정으로 현재 주목받고 있다. 하지만 열가소성 수지는 전자기장에 영향을 받지 않기 때문에 유도 용접은 서셉터(Susceptor)라는 발열체가 필요하다. 고품질 접합을 목표로 연구가 진행되고 있지만, 결국 발열체라는 이물질이 들어가기 때문에 기준이 필요하다. 시편의 제작과 시험은 ASTM D5868에 근거하여 진행된다. 본 논문에서 평가 기준은 용접된 접합면의 상태와 기공률, 전단강도로 총 3가지를 근거로 판단할 것을 제안한다. 용접되는 접착면은 용융되고 냉각되면서 고형화가 되기 때문에 급격한 온도 변화는 기공을 발생시킬 수 있다. 또한 가열이 균일하지 않다면 원하는 성능을 기대하기 힘들다. PA6 (CF 30%) 엔지니어링 플라스틱을 이용하여 서셉터 제작과 유도 용접 그리고 성능 검증으로 진행하였다.

• Journal of the Korean Wood Science and Technology
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• 제50권2호
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• pp.134-147
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• 2022

The objective of this study is to determine the effect of fiber direction arrangement and layer composition of hybrid bamboo laminate boards on the physical and mechanical properties. The raw material used was tali bamboo (Gigantochloa apus (J.A. & J.H. Schultes) Kurs) rope in the form of flat sheets (zephyr) and falcata veneer (Paraserianthes falcataria (L) Nielsen). Zephyr bamboo was arranged in three layers using water-based isocyanate polymer (WBPI) with a glue spread rate of 300 g/m². There were variations in the substitution of the core layer with falcata veneers (hybrid) as much as two layers and using a glue spread rate of 170 g/m². The laminated bamboo board was cold-pressed at a pressure of 22.2 kgf/cm² for 1 h, and the physical and mechanical properties were evaluated. The results showed that the arrangement of the fiber direction significantly affected the dimensional stability, modulus of rupture, modulus of elasticity, shear strength, and screw withdrawal strength. However, the composition of the layers had no significant effect on the physical and mechanical properties. The bonding quality of bamboo laminate boards with WBPI was considered to be quite good, as shown by the absence of delamination in all test samples. The bamboo hybrid laminate board can be an alternative based on the physical and mechanical properties that can meet laminated board standards.

• 산업과 과학
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• 제3권3호
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• pp.14-19
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• 2024

현재 마이크로 LED (Light Emitting Diode)는 디스플레이와 함께 조명 분야에서 관심을 받고 있으며, 높은 휘도, 빠른 동작 속도, 에너지 효율, 오랜 시간 동작 등의 장점을 가지고 있다. 스마트폰, 텔레비젼, 웨어러블 전자소자 등에서 새로운 혁신을 불러올 것으로 예측된다. 이러한 마이크로 디스플레이는 마이크로미터 크기의 LED 소자들로 이루어진 픽셀로 구현되며, 자체적으로 빛을 내는 자체발광형 디스플레이다. 주요 제조 공정으로는 결정성장, 패터닝과 식각, 칩 분리와 전사, 본딩과 배선, 패널 조립과 봉지, 검사와 품질 관리 등으로 구분할 수 있다. 최근 몇 년 동안 이 기술은 빠른 속도로 발전했으며, 기업들이 이러한 분야에의 투자를 확대하고 있다. 최신 시장 조사 결과에 의하면, 마이크로 LED 디스플레이 시장은 지속적으로 성장할 것으로 관측되고 있으며, 주요 발전 방향은 제조공정 개선, 소재 혁신, 구동 기술 발전 등으로 요약할 수 있다. 이러한 연구를 통해 상용화가 가속화되어 높은 성능과 다양한 응용 가능성으로 디스플레이 산업의 혁신을 이끌 것이라 판단된다.