Abstract
Experimental scanning tunneling microscopy (STM) images of bilayer graphene grown via thermal decomposition of Si from SiC display local patterns that suggest the presence of certain types of defects. One common pattern shows threefold (pseudo-sixfold) symmetry, a dark contrast in the center, and a local sqrt(3) by sqrt(3) (rotated 30 degrees) modulation of the graphene structure. Density functional theory calculations were used to study the electronic structure of bilayer graphene with Mo and Si impurities present in various positions compatible with this pseudo-sixfold symmetry. STM images were simulated, based on the the local density of states. The best agreement with experiment is found for an intercalated Mo atom below the center of a hexagon in the top layer and above a C in the bottom layer. While perfect agreement is not obtained, the results suggest that a state or states involving hybridization between m (not equals) 0 transition metal d states and C 2p states is responsible for the defect patterns observed in the STM image.
Published Version
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