(393r) Multiscale Thermal Transport Model for Nano Scale Graphene Systems

Graphene [1], a monolayer of hexagonally sp²-bonded carbon atoms, has been attracting great interest because of its elegant properties, such as superior thermal conductivity and excellent mechanical strength [2,3]. These properties are extremely useful in the nano-electronics industry, where the relevant dimensions are steadily decreasing into the nano-scale region with stringent operating conditions including high thermal gradients. Thus, a suitable strategy for thermal management is urgently required to introduce a paradigm shift in this industry. However, the thermal phenomena in graphene are not well understood once it is bonded with a substrate, as the thermal conductivity falls to about one-fifth of its suspended state conductivity, which will have major effects on its viability as a next generation material [4].

In this study, we attempt to develop a multiscale model spanning from the molecular to the mesoscale to understand the process of the thermal propagation in graphene sheets at the nano-scale to obtain successful design criteria for optimized graphene based devices. We constructed a preliminary molecular model to explore the thermo-mechanical properties of suspended graphene sheets, illustrating that defects such as grain boundaries influence heat transfer compared to pristine graphene structures [5]. We also developed a mesoscale thermal model utilizing a descritization of Boltzmann transport equation called the lattice Boltzmann method (LBM) for primary heat carriers (phonons and electrons) in the nano-scale thermal modeling for various test materials including silicon nano-wires [6]. This work will focus on extending and hybridizing the molecular/mesoscale models to multi-layered graphene films of practical interest including realistic grain boundary orientations and distributions. The molecular model will act as a bridge between nano and micro scale heat transfer by transferring accurate material information to implement the rules for LBM. This study will provide a deeper understanding of the integrated thermal performance of hierarchically arranged materials, which greatly depends not only on the properties of their individual constituents but also on their morphology and interfacial characteristics. The results will also allow the use of composite structures to precisely control thermal conductivity depending on the system requirements.

[1]      A. K. Geim, K. S. Novoselov,  Nature Materials, 6, 183 (2007).

[2]     R. Grantab, V. B. Shenoy, and R. S. Ruoff, Science, 12, 946 (2010).

[3]     S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C. N. Lau, and A. A. Balandin, Nano Letters, 8, 902 (2008)

[4]     Y.I. Jhon, S.E. Zhu, J.H. Ahn, and M.S. Jhon, Carbon (accepted)

[5]     J.H. Seol, I. Jo, A.L. Moore, L. Lindsay, Z. H. Aitken, M.T. Pettes, X. Li, Z. Yao, R. Huang, D. Broido, N. Mingo, R.S. Ruoff, L. Shi, Science, 328, 213 (2010)

[6]     S.S. Ghai, W.T. Kim, R.A. Escobar, C.H. Amon, and M.S. Jhon, J. Appl. Phys., 97, 10P703 (2005)