Center for Functional Nanomaterials Seminar

We have studied graphene growth on Ni(111) using Scanning Tunneling Microscopy (STM). Metal catalysts such as Fe, Co, and Ni are frequently used for the growth of carbon nanotubes and large-scale graphene wafers. The initial atomic-scale growth processes of graphitic carbon on these catalysts are however not well understood. Our atomic level STM studies show that a Ni-carbide surface phase and graphene can coexist. We show that the carbide phase lies in the same surface layer and the two phases match perfectly at their boundary forming a 2D-coincidence lattice that facilitates the transformation of surface carbide into graphene upon annealing to ~ 900K. Furthermore, the carbide phase imposes the orientation of the graphene layer relative to the Ni(111)-substrate, confirming the importance of the carbide phase in the formation of the graphene layer. These atomic resolved STM studies are the first direct evidence that the graphene sheet is evolving from surface carbide. Similar mechanisms may also be relevant for the growth of carbon nanotubes. Defects produced in graphene during epitaxial growth on Ni(111) substrate affects the electronic structure of graphene. We have also studied the atomic structures of defects produced in graphene using STM. We have discovered for the first time extended line defects in graphene. These 1D structures are the consequence of domain boundaries between graphene-sheets occupying different registry relative to the nickel substrate. Atomic resolution STM showed that the line defect consists of fully sp2 hybridized carbon arranged in pentagons and octagons. Density functional theory showed that these defects have a high density of electronic states at the Fermi-level. The wavefunctions of these electronic states at the defect decay exponentially into the graphene lattice causing a local doping in the vicinity of the defect. Finally, the stability of the Ni-graphene interface is studied by Auger electron spectroscopy (AES), Temperature p