Linear and Nonlinear Thermal Transport in Graphene: Molecular Dynamics Simulations
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Linear and Nonlinear Thermal Transport in Graphene: Molecular Dynamics Simulations Bo Qiu,† Yan Wang,† and Xiulin Ruan∗,†,‡ School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA, and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA E-mail: [email protected]
Abstract In this work, we perform molecular dynamics (MD) simulations to study the linear thermal transport in suspended graphene and the nonlinear thermal transport phenomena in graphene nanoribbons (GNR). We use spectral energy density analysis to quantitatively address the relative importance of different types of phonon in thermal transport in suspended graphene. Negative differential thermal conductance (NDTC) and thermal rectification in graphene nanoribbons have been studied using nonequilibrium molecular dyanmics simulations. Ballistic transport regime, sufficient temperature nonlinearity and asymmetry are found to be necessary conditions for the onset of these behaviors.
Introduction Despite extensive investigations on the electronic transport in graphene, many issues of thermal transport still remain unclear. So far, very few measurements on the thermal conductivity κ of graphene have been done due to many challenges. Several groups 1–3 have reported κ of suspended single-layer graphene (SLG) at elevated temperatures with values between 1800 and 5300 W/m K at room temperature. In order to understand the unique 2D thermal transport in graphene, a few theoretical approaches have been proposed. Only a few predictions can match with experimental data for suspended graphene. Among them, Nika et al 4 and Klemens 5 suggested negligible contribution from out-of-plane acoustic (ZA) phonons due to their low group velocity. Lindsay et al 6 used a Fermi’s golden rule approach to accurately account for the three-phonon scattering process, in which a mirror-symmetry is assumed and higher-order phonon scattering is neglected. Their results suggested that the majority heat is carried by ZA ∗ To
whom correspondence should be addressed of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA ‡ Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA † School
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phonons attributed to their large density of states and restricted phonon scattering. It is evident that agreement on the relative importance of individual phonon modes to the thermal conductivity in suspended graphene has not been reached. On the other hand, thermal transport processes out of the linear-response regime such as negative differential thermal conductance (NDTC) and thermal rectification may lead to revolutionary advancements in nanoscale thermal management and thermal signal manipulation. 7–9 NDTC, similar to its electrical counterpart, is a transport process that heat current decreases with increasing temperature bias applied on the two ends of a system. Thermal rectification refers to a diode like behavior where heat propagation is faster in one direction than the opposite. Rece
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