Maximization of Thermal Conductance at Interfaces Via Exponentially Mass-Graded Interlayers

Abstract

We propose a strategy to potentially best enhance interfacial thermal transport through solid-solid interfaces by adding nano-engineered, exponentially mass-graded intermediate layers. This exponential design rule results in a greater enhancement than a linearly mass-graded interface. By combining calculations using non-equilibrium Green's functions (NEGF) and non-equilibrium molecular dynamics (NEMD), we investigated the role of impedance matching and anharmonicity in the enhancement in addition to geometric parameters such as the number of layers and the junction thickness. Our analysis shows that the effect on thermal conductance is dominated by the phonon thermalization through anharmonic effects, while elastic phonon transmission and impedance matching play a secondary role. In the harmonic limit, increasing the number of layers results in greater elastic phonon transmission at each individual boundary, countered by the decrease of available conducting channels. Consequently, conductance initially increases with number of layers due to improved bridging, but quickly saturates. The presence of slight anharmonic effects (at very low temperature, T = 2 K) turns the saturation into a monotonically increasing trend. Anharmonic effects can further facilitate interfacial thermal transport through the thermalization of phonons at moderate temperatures. 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. It follows that at a particular temperature, there exists a corresponding junction thickness at which thermal conductance is maximized.

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Document Details

Document Type
Technical Report
Publication Date
Feb 27, 2019
Accession Number
AD1099289

Entities

People

  • Avik W. Ghosh
  • Carlos A. Polanco
  • Jingjie Zhang
  • Nam Q. Le
  • Pamela M. Norris
  • Rouzbeh Rastgarkafshgarkolaei

Organizations

  • United States Naval Research Laboratory

Tags

Communities of Interest

  • Advanced Electronics

DTIC Thesaurus Topics

  • Acoustic Impedance
  • Chemical Vapor Deposition
  • Chemistry
  • Conduction (Heat Transfer)
  • Crystal Structure
  • Energy
  • Fabrication
  • Frequency
  • Heat Transfer
  • Low Temperature
  • Materials
  • Materials Science
  • Semiconductor Devices
  • Semiconductors
  • Simulations
  • Thermal Conductivity
  • Thermal Resistance

Fields of Study

  • Physics

Readers

  • Fluid Dynamics.
  • Materials Science and Engineering.
  • Quantum Dot Semiconductor Device Photonics and Graphene Optoelectronic Materials and THz Physics.