Optimizing the interfacial thermal conductance at gold-alkane junctions from 'First Principles'

TL;DR

This study uses first-principles calculations to analyze how end-group chemistry affects thermal conductance at gold-alkane interfaces, revealing an optimal bond and mass configuration for maximum heat transfer.

Contribution

It introduces a method combining NEGF and DFT to predict and optimize interfacial thermal conductance based on chemical and physical parameters.

Findings

Thermal conductance peaks at specific mass and bond strength values.

DMM provides an upper bound for elastic phonon transport in the system.

Optimal interface properties can be identified for enhanced heat transfer.

Abstract

We theoretically explore the influence of end-group chemistry (bond stiffness and mass) on the interfacial thermal conductance at a gold-alkane interface. We accomplish this using the Non-Equilibrium Green's Function (NEGF) coupled with first principle parameters in Density Functional Theory (DFT) within the harmonic approximation. Our results indicate that the interfacial thermal conductance is not a monotonic function of either chemical parameters, but instead maximizes at an optimal set of mass and bonding strength. This maximum is a result of the interplay between the overlap in local density of states of the device and that in the contacts, as well as the phonon group velocity. We also demonstrate the intrinsic relationship between the Diffusive Mismatch Model (DMM) and the properties from NEGF, and provide an approach to get DMM from first principles NEGF. By comparing the NEGF based DMM conductance and range of conductance while altering the mass and bonding strength, we show that DMM provides an upper bound for elastic transport in this dimensionally mismatched system. We thus have a prescription to enhance the thermal conductance of systems at low temperatures or at low dimensions where inelastic scattering is considerably suppressed.