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Kim, Jeonggeon,Goo, Yong-Rack,Choi, Indae,Kim, Songkil,Lee, Donggeun Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.131 No.-
<P><B>Abstract</B></P> <P>A particle-reinforced composite material is a matrix with thermally conductive particles that has a diverse range of applications from electronics to energy harvesting/storage systems. In the engineering design of a particle-reinforced composite material for application, it is crucial to accurately and practically predict its effective thermal conductivity. Here, we report the development of a simple analytical model for predictions with improved accuracy and applicability. Comprehensive evaluation of existing models was first conducted to clarify their limitations in prediction accuracy and applicability to various experimental conditions. To overcome the challenges of the existing models, our new model was derived to consider the effect of shape, particle aggregation, and mutual interaction of particles on effective thermal conductivity. Lattice Boltzmann simulations were conducted to obtain a quasi-universal coefficient representing interactions of particles, whereas a shape coefficient characterizing microstructures of aggregated particles was obtained from experimental data available from literature. As a result, our model prediction outperformed the existing models in its prediction accuracy, and it could be applicable to any experimental circumstances where previous model predictions are inappropriate to use.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comprehensive evaluation showed that existing models had their conditional limitations. </LI> <LI> The models were unacceptably degraded under conditions for electronics applications. </LI> <LI> We developed a new model to accurately predict effective thermal conductivity. </LI> <LI> The new model was self-consistent and described asymptotic behaviors of existing models. </LI> <LI> With an additional correlation, the new model was reasonably applicable to any conditions. </LI> </UL> </P>
High Resolution Multimodal Chemical Imaging Platform for Organics and Inorganics
Kim, Songkil,Trofimov, Artem,Khanom, Fouzia,Stern, Lewis,Lamberti, William,Colby, Robert,Abmayr, David,Belianinov, Alex,Ovchinnikova, Olga S. American Chemical Society 2019 ANALYTICAL CHEMISTRY - Vol.91 No.19
<P>Chemical analysis at the nanoscale is critical to advance our understanding of materials and systems from medicine and biology to material science and computing. Macroscale-observed phenomena in these systems are in the large part driven by processes that take place at the nanoscale and are highly heterogeneous. Therefore, there is a clear need to develop a new technology that enables correlative imaging of material functionalities with nanoscale spatial and chemical resolutions that will enable us to untangle the structure-function relationship of functional materials. Therefore, here, we report on the analytical figures of merit of the newly developed correlative chemical imaging technique of helium ion microscopy coupled with secondary ion mass spectrometry (HIM-SIMS) that enables multimodal topographical/chemical imaging of organic and inorganic materials at the nanoscale. In HIM-SIMS, a focused ion beam acts as a sputtering and ionization source for chemical analysis along with simultaneous high-resolution surface imaging, providing an unprecedented level of spatial resolution for gathering chemical information on organic and inorganic materials. In this work, we demonstrate HIM-SIMS as a platform for a next-generation tool for an in situ material design and analysis capable of down to 8 nm spatial resolution chemical imaging, layered metal structure imaging in depth profiling, single graphene layer detection, and spectral analysis of metals, metal oxides, and polymers.</P> [FIG OMISSION]</BR>
Focused Electron Beam-Controlled Graphene Field-Effect Transistor
Kim, Songkil The Korean Institute of Electrical and Electronic 2020 전기전자재료학회논문지 Vol.33 No.5
Focused electron beams with high energy acceleration are versatile probes. Focused electron beams can be used for high-resolution imaging and multi-mode nanofabrication, in combination with, molecular precursor delivery, in an electron microscopy environment. A high degree of control with atomic-to-microscale resolution, a focused electron beam allows for precise engineering of a graphene-based field-effect transistor (FET). In this study, the effect of electron irradiation on a graphene FET was systematically investigated. A separate evaluation of the electron beam induced transport properties at the graphene channel and the graphene-metal contacts was conducted. This provided on-demand strategies for tuning transfer characteristics of graphene FETs by focused electron beam irradiation.
3D 비격자 몬테 카를로 방법을 이용한 비가역적 콜로이드 응집체 모사 연구
김송길(Songkil Kim),이광승(Kwang-Seung Lee),이동근(Donggeun Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Insights into the formation and the structure of colloidal aggregates are essential in many fields of science and engineering. Especially, controllability of aggregate structure with adjusting the experimental conditions is very important in fabricating nanoparticle catalysts which can be applied to energy systems like nanofluids, fuel cell and solar cell. In this work, 3D off lattice Monte Carlo simulation was implemented to irreversible cluster-cluster aggregations in the diluted system for different sticking probabilities which determine aggregation kinetics and structure. Firstly, DLCA regime (P<SUB>ij</SUB>=1) and RLCA regime (P<SUB>ij</SUB>=0.05) were simulated to validate the code, and the fractal dimensions for two regimes were obtained 1.8 and 2.1 respectively, which are in good agreement to the previous researches. The structure and kinetics of the aggregates were studied for different sticking probabilities.