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Adsorption Site Selectivity for Thiophene on Reconstructed Si(5 5 12)–2 × 1 Surface
Hahn, Jae Ryang,Bharath, Satyaveda C.,Kim, Gyu-Hyeong,Kim, Ki Wan,Jeong, Sukmin,Pearl, Thomas P. American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.21
<P>The covalent binding of thiophene molecules to a Si(5 5 12)–2 × 1 surface was investigated using scanning tunneling microscopy and density functional theory calculations. The molecular attachment occurred exclusively between the bonding of the 2,5 carbon atoms and the two silicon adatoms without the involvement of the sulfur atom (over 90%). The binding structure formed a di−σ bond with a planar butterfly-like configuration. Adsorption at other sites, including at the dimer, tetramer, or honeycomb rows, occurred much less frequently. Our calculations predicted that the adsorption energies of the thiophene molecules were 1.02–1.56 eV at the adatom, dimer, and tetramer sites. The molecules adsorbed on the honeycomb rows with a low adsorption energy (below 1 eV). The binding modes of the simple aromatic molecules onto the Si(5 5 12)–2 × 1 surface are compared and discussed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-21/jp401932r/production/images/medium/jp-2013-01932r_0005.gif'></P>
3D 적층 STS316L 소재의 저항 점용접 특성 평가
김세현(SeHyeon Kim),김민규(Min-Gyu Kim),황인성(In-Sung Hwang),김동윤(Dong-Yoon Kim),김영민(Young-Min Kim),박지용(Jiyong Park),유지영(Jiyoung Yu) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
최근 다양한 산업에서 기존 가공방식으로는 제작이 어려운 복잡형상을 3D프린팅 방식으로 제작하는 사례가 늘어나고 있다. 특히, 위상 최적화를 통한 형상 제작을 통하여 무게를 감소시키고, 부품 일체화를 통해 기존 부품 용접부의 내구성 문제를 해결할 수 있어 주목을 받고 있다. 하지만, 이러한 장점에도 불구하고, 3D프린팅 방식은 아직 대형 부품을 제작하는데, 재료 및 공정의 한계를 보이고 있어 산업 부품을 제작하기가 적합하지 않다. 이에 일부 주요한 부품을 3D프린팅 기술로 제작하고 대형 부품에 용접하여 제품을 완성하는 기술에 대한 필요성이 대두되고 있다. 따라서 본 연구에서는 대표적인 3D 적층 STS316L과 STS316L 판재 소재에 대하여 각각 동종 소재 조합으로 저항 점용접을 진행하여 3D프린팅 부품의 용접성을 비교하는 연구를 수행하였다. 전극 가압력은 350 kgf로 고정한 후, 용접 전류, 용접 시간에 따라 용접을 진행하여 저항 점용접 로브를 도출 하였다. 용접 후, 단면 분석, 인장전단강도 시험, 조직 분석, 파형 분석을 통하여, 각 소재에 대한 저항 점용접성에 대해 평가를 진행하였다. 파형 분석은 용접 중 전류, 전압 신호를 측정하여, 동저항, 전력 신호를 도출 한 후, 거동에 대한 분석을 진행하여 3D프린팅 공정의 용접성을 확인하였다.
유한요소해석을 이용한 표면적용을 위한 자기 복합재료의 설계
김승호(Seung-Ho Kim),H. Thomas Hahn,허훈(Hoon Huh) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The present paper explores the use of magnetic composites reinforced by permanent magnetic particles for a number of surface applications including adhesive joints, coatings and reduced-friction surfaces. When magnetic composites are used as an adhesive with magnetically permeable adherends, the composite can provide additional bonding stresses through magnetic attraction. The same benefits are expected when the composite is coated on magnetic surfaces. Composite coatings can also be used to create reduced-friction surfaces through magnetic repulsion. In this paper, a finite element method has been used to design the magnetic composite. Magnetic characteristics of magnetic composites are calculated through electromagnetic finite element analysis. The design parameters are the morphology, spatial distribution, size and volume fraction of magnet particles. Design time and costs in the development stage of composites can be minimized through optimized process conditions calculated from finite element simulations.
The Optimization of a Woodpile Photonic Crystal and its Negative Refractive Behavior
윤성기,김현중,Dong Eun (Erica) Shim,H. Thomas Hahn 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3
In this paper, three-dimensional woodpile photonic crystals (PhCs) are investigated for various applications. In order to obtain PhCs with maximal photonic band gap, we optimize the size of 3D woodpile PhC by employing design of experiments. From the response surface model, which is a function of geometric design parameters, the photonic band gap is readily predicted, and the size ratios can be optimized. In addition, the PhC exhibits a negative refractive behavior due to its highly-anisotropic and wavelength-dependent dispersion properties. In order to predict the refracting angles of light inside the PhC, we investigate equi-frequency surfaces throughout the Brillouin zone. To verify that the refracting angles from the band structure calculation are reasonable, we perform finite difference time domain (FDTD) simulations. The tendency of the refracting angle with respect to wavelength and incident angle is examined by showing the wave propagation inside the PhC come from the FDTD simulations.