Tuning electronic heat transport in graphene/metal heterostructures with ultralow thermal conductivity

TL;DR

This study introduces graphene/metal heterostructures with ultralow thermal conductivity and significant electronic heat transport, offering potential for thermoelectric applications by overcoming limitations of prior materials.

Contribution

It demonstrates a new class of heterostructures with ultralow thermal conductivity and notable electronic heat transport, achieved through specific fabrication methods and material choices.

Findings

Achieved ultralow thermal conductivity of 0.06 W/m·K in evaporated samples.

Found about 50% of heat is carried by electrons in sputtered samples.

Attributed electronic heat transport to atomic-scale pinholes in graphene.

Abstract

Prior ultralow thermal conductivity materials are not suitable for thermoelectric applications due to the limited electronic transport in the materials. Here, we present a new class of ultralow thermal conductivity materials with substantial electronic heat transport. Our samples are graphene/metal heterostructures of transferred graphene and ultrathin metal films (Pd, Au and Ni) deposited by either thermal evaporation or rf magnetron sputtering. For the evaporated samples, we achieve an ultralow thermal conductivity of 0.06 W m-1 K-1, with phonons as the dominant heat carriers. The ultralow thermal conductivity is due to a huge disparity in phonon energy in graphene and metals. Interestingly, for the sputtered samples, we find that about 50 % of heat is carried by electrons, even when thermal conductivity is about 0.1 W m-1 K-1. We attribute the electronic contribution to transmission of electrons across atomic-scale pinholes in graphene. With the ultralow thermal conductivity and substantial electronic transport, the new materials could be explored for thermoelectric applications.