Phonon-mediated thermal transport at exponentially mass-graded interfaces: A computational study

Authors:Rastgarkafshgarkolaei, Rouzbeh, Department of Mechanical and Aerospace EngineeringUniversity of Virginia Zhang, Jinjie, Department of Electrical and Computer EngineeringUniversity of Virginia Polanco, Carlos A., Materials Science and Technology DivisionOak Ridge National Laboratory Le, Nam Q., National Research Council Research Associateship ProgramsU.S. Naval Research Laboratory, Ghosh, Avik, Department of Electrical and Computer Engineering University of Virginia Norris, Pamela, Department of Mechanical and Aerospace Engineering University of Virginia ORCID icon

We numerically investigate thermal transport at solid-solid interfaces with graded intermediate layers whose masses vary exponentially from one side to the other. Using Non-Equilibrium Green's Function and Non-Equilibrium Molecular Dynamics simulations, we show that an exponentially mass-graded junction with a finite thickness can result in 68% of enhancement in thermal conductance larger compared to a single bridging layer (29%) and a linear mass-graded junction (64%) of similar thickness. We examine how the thermal conductance at such interfaces is influenced by geometric qualities and strength of anharmonicity. For geometric properties, we tested the effects from number of layers and the junction thickness. In the absence of anharmonicity, increasing the number of layers results in better elastic phonon transmission at each individual boundary, countered by the decrease of available conducting channels. Consequently, in the harmonic regime, conductance initially increases with number of layers due to better bridging, but quickly saturates. The presence of slight anharmonic effects (at ultra-low temperature T = 2 K) turns the saturation into a monotonically increasing trend. Anharmonic effects can facilitate interfacial thermal transport through the thermalization of phonons. At high temperature, however, the role of anharmonicity as a facilitator of interfacial thermal transport reverses. Strong anharmonicity introduces significant intrinsic resistance, overruling the enhancement in thermal conduction at the boundaries. Our analysis shows that in our model Lennard-Jones system, the influence of a mass-graded junction on thermal conductance is dominated by the phonon thermalization through anharmonic effects, while elastic phonon transmission plays a secondary role. It follows that at a particular temperature, there exists a corresponding junction thickness at which thermal conductance is maximized.

All rights reserved (no additional license for public reuse)
Source Citation:

Rastgarkafshgarkolaei, Rouzbeh, Jingjie Zhang, Carlos A. Polanco, Nam Q. Le, Avik W. Ghosh, and Pamela M. Norris. “Phonon-mediated thermal transport at exponentially mass-graded interfaces: A computational study.”, Physics, arXiv:1809.04748 (2018), 1-14. Available:

Published Date:
September 13. 2018