(451g) Two-Dimensional Crystalline Domains Embedded In Graphene Bilayers: Structure and Properties

Exposure of graphene bilayers to fluxes of atomic hydrogen leads to H chemisorption onto the outer surfaces of the graphene layers. Certain hydrogenation patterns favor the formation of covalent interlayer C-C bonds, which have been shown to stabilize the hydrogenated surfaces. The hydrogenation of graphene bilayers and the associated interlayer bonding may generate two-dimensional (2D) crystalline domains of sp³-hybridized carbon atoms. These 2D crystals have structures that resemble those of various carbon allotropes under different plane orientation.

In this presentation, we report results of a systematic computational analysis of the atomic and electronic structures and properties of such 2D crystalline carbon nanomaterials. The analysis is based on structural relaxation and computation of electronic and mechanical properties of these materials. The atomic and electronic structure of the materials is determined according to first-principles density functional theory (DFT) calculations, while the mechanical properties are computed using classical molecular-dynamics (MD) simulations according to a reliable reactive bond order potential.

The crystalline structure of the interlayer-bonded configurations is determined by the plane stacking in the pristine bilayer and by the hydrogenation patterns on the surfaces. DFT calculations predict the configurations that lead to the most thermodynamically favorable phases. DFT also is used to compute the band structure of these thermodynamically stable phases; all of the 2D crystalline configurations examined constitute insulators with band gaps of approximately 3 eV, which is consistent with the electronic behavior of sp³-bonded carbon allotropes. MD simulations of dynamic deformation, under conditions of constant tensile strain rate and temperature, allow for predictions of mechanical properties of these materials, such as their Young modulus, tensile strength, and fracture strain. These mechanical properties are dependent on the materials’ crystalline structure and on the applied tensile stress.