(485f) Thermal Transport and Electronic Properties of Pure and Hydrogenated Electron-Irradiated Graphene

Defect engineering through irradiation processes and chemical functionalization of graphene are promising routes for fabrication of carbon nanostructures and two-dimensional metamaterials with unique properties and function. In previous computational studies, we reproduced experimentally observed structures of irradiated graphene sheets through introduction of random distributions of vacancies in the honeycomb lattice of graphene and proper structural relaxation. We found that a vacancy-induced crystalline-to-amorphous transition in graphene occurs for an inserted vacancy concentration between 5% and 10%. This amorphization transition is accompanied by a brittle-to-ductile transition in the mechanical response of the irradiated graphene sheets as well as introduction of localized electronic states near the Fermi level.

In this presentation, we report results from a systematic analysis of thermal transport in these electron irradiated, including irradiation-induced amorphous, graphene sheets with emphasis on the dependence of their thermal conductivity on the inserted defect density. Furthermore, we use hydrogenation as a means of studying the effects of chemical functionalization and defect passivation on the electronic structure and thermal transport properties of irradiated graphene. Using molecular-dynamics simulations according to a reliable bond-order potential, we prepare and equilibrate the irradiated configurations, pure and hydrogenated, and subsequently conduct non-equilibrium molecular-dynamics (NEMD) simulations at constant heat flux. While the thermal conductivity of irradiated graphene decreases precipitously from that of perfect graphene’s upon introducing a low vacancy concentration (2% or less) in the graphene lattice, further decrease of the thermal conductivity with increasing vacancy concentration follows a weaker, almost linear dependence until the amorphization threshold. Beyond the onset of amorphization, the thermal conductivity of irradiated graphene exhibits a second, much weaker almost linear dependence on the vacancy concentration. Furthermore, we find that hydrogenation does not affect the thermal conductivity of the irradiated graphene sheets if the hydrogenated C atoms remain sp²-hybridized. However, upon inducing sp³ hybridization of these C atoms with further hydrogenation, the thermal conductivity of the irradiated sheets is reduced only if the irradiated structure remains crystalline. Beyond the amorphization threshold, defect passivation by hydrogenation does not have any detectable effect on the thermal conductivity of irradiated graphene. Finally, based on first-principles density functional theory calculations of the electronic structure of unpassivated as well as hydrogen-passivated irradiated graphene structures, we assess the potential for tuning the electronic properties of these defective, functionalized graphenes.