Thermal transport of amorphous carbon and boron-nitride monolayers

TL;DR

This study calculates the in-plane thermal conductivity of amorphous 2D carbon and boron nitride monolayers, revealing ultralow, temperature-independent values due to structural disorder and vibrational localization, with implications for thermal management.

Contribution

It provides the first detailed computational analysis of thermal transport in amorphous 2D carbon and boron nitride monolayers, highlighting their ultralow, temperature-independent thermal conductivity.

Findings

Thermal conductivity of amorphous carbon and BN monolayers is about two orders of magnitude lower than crystalline forms.

Thermal conductivity remains nearly constant across temperature variations.

Vibrational localization is prominent in amorphous BN, while amorphous carbon exhibits a unique high-frequency mode.

Abstract

Two-dimensional (2D) materials like graphene and h-BN usually show high thermal conductivity, which enables rich applications in thermal dissipation and nanodevices. Disorder, on the other hand, is often present in 2D materials. Structural disorder induces localization of electrons and phonons and alters the electronic, mechanical, thermal, and magnetic properties. Here we calculate the in-plane thermal conductivity of both monolayer carbon and monolayer boron nitride in the amorphous form, by reverse nonequilibrium molecular dynamics simulations. We find that the thermal conductivity of both monolayer amorphous carbon (MAC) and monolayer amorphous boron nitride (ma-BN) are about two orders of magnitude smaller than their crystalline counterparts. Moreover, the ultralow thermal conductivity is independent of the temperature due to the extremely short phonon mean free path in these amorphous materials. The relation between the structure disorder and the reduction of the thermal conductivity is analyzed in terms of the vibrational density of states and the participation ratio. ma-BN shows strong vibrational localization across the frequency range, while MAC exhibits a unique extended G' mode at high frequency due to its sp2 hybridization and the broken E2g symmetry. The present results pave the way for potential applications of MAC and ma-BN in thermal management.