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Coefficient of Thermal Expansion Measurements for Freestanding Nanocrystalline Ultra-Thin Gold Films
Alexander Elceario Mag-isa,오충석,장봉균,김재현,이학주 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
The out-of-plane coefficient of thermal expansion (CTE) measurement method, which is named the thermal bulge method, was used to measure the linear CTE values for freestanding nanocrystalline ultra-thin gold films with thicknesses ranging from 115 to 1200 nm. White light interferometry was used to determine the out-of-plane thermal deformation as a function of temperature. The thermal strain showed a linear behavior in the temperature range of 20 to 100oC, but varied with the thickness (or grain size) of the specimen. The grain sizes, which were measured by transmission electron microscopy (TEM), showed a strong correlation with the CTE: Specimens with larger grain sizes (44 to 98 nm) had greater CTE values (9.6 to 13.6 ppm/oC). Starting from the CTE values for fine-grained materials, the CTE of nanocrystalline gold films increased with increasing grain size and approached the CTE of bulk gold. The thermal bulge method, which was previously developed by the authors, allowed for direct, repetitive, reliable, and quick measurement of the CTE values of ultra-thin gold films.
Hwangbo, Y.,Lee, C.K.,Mag-Isa, A.E.,Jang, J.W.,Lee, H.J.,Lee, S.B.,Kim, S.S.,Kim, J.H. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.77 No.-
We demonstrate a simple and easy technique to reliably count the number of layers in graphenes with stacking faults. Using lasers with wavelengths of 514 and 633nm, the optical transmittances of multilayer graphene with Bernal, rhombohedral and artificial stacking orders were systematically measured depending on the number of layers. It was found that the optical transmittance of the multilayer graphene is linearly proportional to the number of layers up to 7 regardless of its stacking order. Measurement of optical transmittance can be a useful approach to reliably determine the number of layers in multilayer graphene, thus aiding investigation of its layer-dependent properties and applications.
Dimensional dependence of phonon transport in freestanding atomic layer systems.
Kim, Duckjong,Hwangbo, Yun,Zhu, Lijing,Mag-Isa, Alexander E,Kim, Kwang-Seop,Kim, Jae-Hyun RSC Pub 2013 Nanoscale Vol.5 No.23
<P>Due to the fast development of nanotechnology, we have the capability of manipulating atomic layer systems such as graphene, hexagonal boron nitride and dichalcogenides. The major concern in the 2-dimensional nanostructures is how to preserve their exceptional single-layer properties in 3-dimensional bulk structures. In this study, we report that the extreme phonon transport in graphene is highly affected by the graphitic layer stacking based on experimental investigation of the thermal conduction in few-layer graphene, 1-7 layers thick, suspended over holes of various diameters. We fabricate freestanding axisymmetric graphene structures without any perturbing substrate, and measure the in-plane transport property in terms of thermal conduction by using Raman spectroscopy. From the difference in susceptibility to substrate effect, size effect on hot-spot temperature variation and layer number dependence of thermal conductivity, we show that the graphitic membranes with 2 or more layers have characteristics similar to 3-dimensional graphite, which are very different from those of 2-dimensional graphene membranes. This implies that the scattering of out-of-plane phonons by interlayer atomic coupling could be a key mechanism governing the intrinsic thermal property.</P>
Cutting Flat Panel Display Glass Substrate susing Nd:YAG Laser
Cheong, Seon-Hwan,Ro, Seung-Hoon,Choi, Seong-Dae,Alexander Mag-isa 한국공작기계학회 2006 한국공작기계학회 추계학술대회논문집 Vol.2006 No.-
The production of large size glass substrates is making the manufacture of flat panel displays (FPD) more cost effective by allowing more yields in a single sheet. Glass cutting is a fundamental step in sizing the substrates needed for the FPD and should produce a cut with good edge quality. Poor cuts will inevitably result in reduced strength and an origin for crack propagation. This study involves the use of a continuous Nd:YAG laser beam for cutting soda-lime glass (typically used in Plasma Display Panel or PDP optical filters) and alkaline earth boro-aluminosilicate glass substrates used for active matrix liquid crystal displays (AMLCD). Various techniques in conjunction with the laser were explored including pre-scoring and an increased temperature gradient. Using microscopy and other tests, results were compared with that produced using conventional scribe and break method. All tests were conducted on a prototype glass cutting machine capable of cutting substrates using laser or by means of tungsten carbide coated scribing wheel to ensure that all other cutting conditions remains the same for each method.
구리 박막의 그래핀(Graphene) 및 열처리에 의한 전기적-기계적 물성 영향에 관한 연구
김상민(Sang-Min Kim),황보윤(Yun Hwangbo),맥이사알렉산더(Mag-isa Alexan),오충석(Chung-Seog Oh),이학주(Hak-Joo Lee) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
The important use of copper thin films as a reliable interconnect material for integrated circuits is hampered by reliability issues one of the most noted of which is the increased resistivity at the micro and nano scale attributed to grain boundary scattering. The usual approach to this problem is the annealing of copper at a high temperature. Graphene growth on copper via Thermal CVD includes the annealing of copper. This work examines the effects of graphene growth on the resistivity and mechanical properties of copper. Resistance measurement coupled with Digital Image Correlation were performed on dog-bone shaped specimens of copper (18 um thick), thermally anneal copper and graphene growth copper. Raman spectroscopy was performed to examine the graphene layer while an AFM was used to examine the surface topography of the copper and annealed copper surfaces.