Structural, Vibrational, and Thermal Properties of Nanocrystalline Graphene in Atomistic Simulations

Two different methods have been applied to create differently structured nanocrystalline graphene samples used in molecular dynamics simulations. In the first method, graphene sheets are generated by grain growth from individual nucleation seeds. The second method applies Voronoi tessellation to define single crystalline domains in the simulation cells. The differently generated nanocrystalline graphene sheets show significant variations in the grain size distribution and the shape of the crystalline domains. Furthermore, out-of-plane corrugation is found to be more pronounced in samples generated by the Voronoi method, in particular for small grain sizes (<= 14 nm). Marginal differences are observed in the distribution of polygonal rings in the grain boundaries which might result from the geometrical shape of the grain boundaries. Thermal conductivity has been determined using the approach-to-equilibrium molecular dynamics formalism. A lower thermal conductivity is observed in Voronoi samples for grain sizes between 5 and 14 nm which is attributed to the stronger out-of-plane corrugation.