Ballistic to diffusive crossover of heat flow in graphene ribbons

TL;DR

This study investigates heat transport in graphene nanostructures, revealing a transition from ballistic to diffusive regimes influenced by dimensions and edge disorder, with implications for thermal management in nanoscale devices.

Contribution

It demonstrates the crossover from ballistic to diffusive heat flow in graphene ribbons and quantifies how width and edge disorder control thermal conductivity.

Findings

Short graphene samples reach ~35% of ballistic conductance at room temperature.

GNRs exhibit width-dependent thermal conductivity scaling as W^{1.8}.

Thermal conductivity in 65-nm GNRs is about 100 W/m/K.

Abstract

Heat flow in nanomaterials is an important area of study, with both fundamental and technological implications. However, little is known about heat flow in two-dimensional (2D) devices or interconnects with dimensions comparable to the phonon mean free path (mfp). Here, we find that short, quarter-micron graphene samples reach ~35% of the ballistic heat conductance limit up to room temperature, enabled by the relatively large phonon mfp (~100 nm) in substrate-supported graphene. In contrast, patterning similar samples into nanoribbons (GNRs) leads to a diffusive heat flow regime that is controlled by ribbon width and edge disorder. In the edge-controlled regime, the GNR thermal conductivity scales with width approximately as ~W^{1.8+/-0.3}, being about 100 W/m/K in 65-nm-wide GNRs, at room temperature. Manipulation of device dimensions on the scale of the phonon mfp can be used to achieve full control of their heat-carrying properties, approaching fundamentally limited upper or lower bounds.