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3차원 유한요소법을 이용한 교정용 마이크로임플란트 식립 시의 피질골 스트레인 해석
남옥현,유원재,경희문 대한치과교정학회 2008 대한치과교정학회지 Vol.38 No.4
식립 후 힘의 부하가 조기에 이루어지는 마이크로임플란트의 경우 식립 시의 골응력 혹은 스트레인의 관리가 그 안정성에 있어 중요한 요인으로 작용할 수 있다. 이에 본 연구에서는 3D 유한요소법을 사용하여 교정용 마이크로임플란트 식립 시 피질골에 발생하는 응력(스트레인)을 해석하였다. 0.9 mm 직경으로 미리 드릴링한 1 mm 두께 피질골에 마이크로임플란트(AbsoAnchor SH1312-7, Dentos, Daegu, Korea)가 식립되는 전체 과정(10회전, 식립 깊이 5mm)의 모사를 위해 총 1,800 step의 유한요소해석을 실시하였다. 식립 진행과 더불어 생기는 나사산 주위 피질골의 기하학적 형상변화를 유한요소해석에 반영하기 위하여 지속적인 remesh를 실행하였으며, 빠른 수렴을 위해 마이크로임플란트는 강체로, 피질골은 강소성체로 모델링하였다. 해석 결과, 마이크로임플란트 식립 시 피질골에 발생되는 스트레인은 임플란트 주위골 전체에서 정상적인 골개형을 위한 한계치로 보고되고 있는 4,000μ-strain을 상회하였고, 나사산 첨부 인접골에서는 스트레인이 100% 이상에 달하였다. 계산된 피질골 식립토오크는 약 1.2 Ncm 정도로 가토 경골에 동일 모델의 마이크로임플란트을 식립하며 측정한 값에 약간 미달하였으나 근접한 수치를 보였다. 본 연구를 통해, 마이크로임플란트의 식립과정을 3D 유한요소법으로 재현할 수 있음을 확인하였고, 또한 마이크로임플란트 식립에 의해 피질골에 발생하는 스트레인 크기는 생리적인 골개형을 저해할 수 있는 수준임을 확인할 수 있었다.
Recent Advances in Nonpolar and Semipolar InGaN Light-Emitting Diodes (LEDs).
Jang, Jongjin,Woo, Seohwi,Min, Daehong,Nam, Okhyun American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.3
<P>The III-nitrides have attracted much attention because of their applicability in optoelectronic devices, whose emission wavelengths range from green to ultraviolet light due to their wide band gap. However, conventional c-plane GaN-based devices are influenced significantly by spontaneous and piezoelectric polarization effects, which could pose a limitation for increased luminous efficiency as a result of the quantum confined stark effect. Since the early 2000s, many groups have tried to solve these problems by examining the growth of GaN on non- or semipolar surface planes. High power non- and semipolar LEDs can be realized by the growth of a thick active layer. In addition, it is expected that it is possible to grow nonpolar InGaN LEDs with high quality p-GaN layers due to lower hole activation energy, and also long-wavelength semipolar InGaN LEDs because of the capacity for high indium incorporation in the quantum wells (QWs). However, non- and semipolar structures grown on sapphire substrate usually contain a high density of basal stacking faults and threading dislocations. For this reason, the growth of non- and semipolar GaN-based LEDs on a sapphire substrate has been attempted through the introduction of defect reduction techniques such as epitaxial lateral overgrowth, patterned sapphire substrate and re-growth techniques on a porous GaN layer, etc. Also, some researchers have grown high quality non- and semipolar GaN-based LEDs using non- and semipolar freestanding GaN substrates. In this review paper, we introduce and discuss recent progress in the development of non- and semipolar GaN-based LEDs and freestanding GaN substrates.</P>
Eom, Daeyong,Kim, Jinwan,Lee, Kyungjae,Jeon, Minhwan,Heo, Cheon,Pyeon, Jaedo,Nam, Okhyun American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.7
<P>This study investigates the crystallographic polarity transition of AIN layers grown by high temperature metalorganic chemical vapor deposition (HT-MOCVD), with varying trimethylaluminum (TMAI) pre-flow rates. AIN layers grown without TMAI pre-flow had a mixed polarity, consisting of Al- and N-polarity, and exhibited a rough surface. With an increasing rate of TMAI pre-flow, the AIN layer was changed to an Al-polarity, with a smooth surface morphology. Finally, AIN nano-pillars and nano-rods of Al-polarity were fabricated by etching a mixed polarity AIN layer using an aqueous KOH solution.</P>
GaN Growth on SiC (0001) Substrates by Metal-Organic Chemical Vapor Deposition
Lee, Kyungbae,So, Byeongchan,Lee, Kyungjae,Heo, Cheon,Ko, Kwangse,Jang, Jongjin,Nam, Okhyun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>In this study, the effects of the AlN buffer thickness and off-cut angles of 6H-SiC substrates on the crystallinity of GaN layers deposited via high-temperature metal organic chemical vapor deposition were investigated. The crystallinity of the GaN layers on the on-axis substrates was enhanced as the AlN buffer thickness increased. In contrast, the crystallinity of the GaN layers on the off-axis substrates was improved by applying relatively thinner AlN buffer layers. The strain relaxation of the GaN layers was closely related to the AlN buffer thickness and off-cut angles. Cathodoluminescence measurements revealed that the dark spot densities relative to defects were 1.9x10(8) and 8.9x10(7) cm(-2) for the on-and off-axis substrates, respectively. Cross-sectional transmission electron microscopy images showed that the screw and edge dislocation densities of the GaN layers deposited on off-axis substrates were reduced because of the bending of dislocations, which is due to macro-step bunching.</P>
Heo, Cheon,Jang, Jongjin,Lee, Kyungjae,So, Byungchan,Lee, Kyungbae,Ko, Kwangse,Nam, Okhyun American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.1
<P>We investigated the correlation between the crystal quality and two-dimensional electron gas (2DEG) mobility of an AlGaN/GaN high-electron-mobility transistor (HEMT) structure grown by metal-organic chemical vapor deposition. For the structure with an AlN nucleation layer grown at 1100 degrees C, the 2DEG mobility and sheet carrier density were 1627 cm(2)/V . s and 3 x 23x10(13) cm(-2), respectively, at room temperature. Further, it was confirmed that the edge dislocation density of the GaN buffer layer was related to the 2DEG mobility and sheet carrier density in the AlGaN/GaN HEMT.</P>