Investigation of phonon thermal transport in monolayer and bilayer 2D organic C60 networks

Understanding phonon thermal transport mechanism of novel two-dimensional (2D) organic C-60 networks is crucial for the preparation of functionalized nanoelectronics. In this study, the in-plane thermal conductivities of monolayer and bilayer quasi-hexagonal phase C-60 (QHP C-60) and quasi-tetragonal phase C-60 (QTP C60) are comprehensively investigated and phonon transport mechanisms are thoroughly elucidated. Compared to C-60 single crystals, the thermal conductivities of 2D organic C-60 networks are elevated by 1 similar to 2 orders of magnitude. The thermal conductivities of bilayer C-60 networks are significantly lower than monolayer C-60 networks. Furthermore, thermal transport is mainly dominated by < 10 THz low frequency phonons. The phonon modes of bilayer C-60 networks exhibit the redshift phenomenon, which reduces the phonon group velocity and phonon mean free path. Consequently, the thermal conductivities of bilayer C-60 networks are suppressed. Moreover, the enhancement of interlayer coupling intensifies anharmonic properties and disrupts the low frequency phonon branch, which results in the localization of low frequency phonons to hinder thermal transport in bilayer-QHP C-60 and bilayer-QTP C-60. Further, the bonding interaction is the major contributor of thermal transport in bilayer C-60 networks. The improvement of interlayer coupling fully suppresses the contributions of bonding and nonbonding to degrade the phonon thermal transport.