Resonant phonon modes in fullerene functionalized graphene lead to large tunability of thermal conductivity without impacting the mechanical properties

A Giri and PE Hopkins, JOURNAL OF APPLIED PHYSICS, 125, 205102 (2019).

DOI: 10.1063/1.5094061

We investigate the effects of fullerene functionalization on the thermal transport properties of graphene monolayers via atomistic simulations. Our systematic molecular dynamics simulations reveal that the thermal conductivity of pristine graphene can be lowered by more than an order of magnitude at room temperature (and as much as by similar to 93% as compared to the thermal conductivity of pristine graphene) via the introduction of covalently bonded fullerenes on the surface of the graphene sheets. We demonstrate large tunability in the thermal conductivity by the inclusion of covalently bonded fullerene molecules at different periodic inclusions, and we attribute the large reduction in thermal conductivities to a combination of resonant phonon localization effects, leading to band anticrossings and vibrational scattering at the sp(3) bonded carbon atoms. The torsional force exerted by the fullerene molecules on the graphene sheets and the number of covalent bonds formed between the two carbon allotropes is shown to significantly affect the heat flow across the hybrid structures, while the size of the fullerene molecules is shown to have a negligible effect on their thermal properties. Moreover, we show that even for a large surface coverage, the mechanical properties of these novel materials are uncompromised. Taken together, our work reveals a unique way to manipulate vibrational thermal transport without the introduction of lattice defects, which could potentially lead to high thermoelectric efficiencies in these materials. Published under license by AIP Publishing.

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