Length dependence of the thermal conductance of alkane-based single-molecule junctions: An ab-initio study

TL;DR

This study uses ab-initio methods to analyze how the length and chemical modifications of alkane chains affect their thermal conductance in single-molecule junctions, providing insights for thermal management design.

Contribution

It offers a systematic ab-initio analysis of length and substitution effects on phonon transport in alkane-based molecular junctions, combining DFT and NEGF techniques.

Findings

Thermal conductance is length-independent for chains longer than 5 methylene units.

Phononic metal-molecule coupling strength significantly influences thermal transport.

Substituting hydrogen with fluorine affects phonon transport properties.

Abstract

Motivated by recent experiments, we present here a systematic ab-initio study of the length dependence of the thermal conductance of single-molecule junctions. We make use of a combination of density functional theory with non-equilibrium Green's function techniques to investigate the length dependence of the phonon transport in single alkane chains, contacted with gold electrodes via both thiol and amine anchoring groups. Additionally, we study the effect of the substitution of the hydrogen atoms in the alkane chains by heavier fluorine atoms to form polytetrafluoroethylenes. Our results demonstrate that (i) the room-temperature thermal conductance is fairly length-independent for chains with more than 5 methylene units and (ii) the efficiency of the thermal transport is strongly influenced by the strength of the phononic metal-molecule coupling. Our study sheds new light onto the phonon transport in molecular junctions, and it provides clear guidelines for the design of molecular junctions for thermal management.