459466 Electronic, Mechanical, and Thermal Transport Properties of Hydrogenated Irradiated Graphene

Tuesday, November 15, 2016: 4:00 PM
Golden Gate 7 (Hilton San Francisco Union Square)
Asanka Weerasinghe, Physics, University of Massachusetts Amherst, Amherst, MA, Dimitrios Maroudas, Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA and Ashwin Ramasubramaniam, Mechanical and Industrial Engineering, University of Massachusetts Amherst, Amherst, MA

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 use hydrogenation of irradiated, including irradiation-induced amorphous, graphene as a means of studying the effects of chemical functionalization on its electronic structure and thermomechanical response.. We use molecular-dynamics simulations according to a reliable bond-order potential to prepare the hydrogenated configurations and to carry out mechanical tests of dynamic deformation of the prepared configurations at constant strain rate and temperature. We find that hydrogenation does not affect the ultimate tensile strength (UTS) of the irradiated graphene sheets if the hydrogenated C atoms remain sp2-hybridized. However, upon inducing sp3 hybridization of these C atoms, UTS decreases by about 10 GPa; in spite of this decrease, these hydrogenated defective structures remain remarkably strong. We also find that the fracture strain of the irradiated structures decreases by up to 30% upon hydrogenation independent of the hybridization type. We characterize the fracture mechanisms and analyze the embrittlement effects of hydrogen. In addition, we report results from thermal transport analysis of the defective graphene sheets with emphasis on the effects of defect density and the extent of hydrogenation and the resulting hybridization of the hydrogenated C atoms on the thermal conductivity of the graphene sheets, computed based on an equilibrium Green-Kubo approach. Finally, based on first-principles density functional theory calculations of the electronic structure of unpasssivated as well as hydrogenated irradiated graphene structures, we assess the potential for tuning the electronic properties of these defective, functionalized graphenes.

Extended Abstract: File Not Uploaded