Defects in graphene are of interest for their effect on electronic transport in this two-dimensional material. Point defects of typically two-fold and three-fold symmetry have long been observed in scanning tunneling microscopy (STM) studies of graphite. In epitaxial graphene grown at high temperatures on mechanically-polished SiC(0001), we observe a 6-fold "flower" defect by STM, with enhanced differential tunnel conductance over the 2 nm extent of the defect. Density functional theory calculations suggest that the defect is a rotational grain boundary made up of five- and seven-membered carbon rings. The observed defect is the smallest member of a family of rotational grain boundaries characterized by two integers, (m,n), which correspond to rotations of the hexagonal lattice within the core of the defect by (n/m)x(60 degrees) with respect to the outside lattice. Simulated STM topographs of the (2,1) rotational defect are in agreement with experiment.
Citation: Physical Review B
Pub Type: Journals
graphene, defects, grain boundaries, STM imagery