Observation and investigation of graphite superlattice boundaries by scanning tunneling microscopy

In this article, we report on scanning tunneling microscopy (STM) observations of several different kinds of superlattice boundaries on highly-oriented pyrolytic graphite (HOPG) including an array of bead-like structures, a monolayer deep trench, a zig-zag shaped termination, and a plain boundary without features. Results of a simulation model show that a top rotated graphite layer with a straight boundary does not necessarily lead to the zig-zag shaped boundary of the resulting superlattice as has been previously claimed. The formation of the bead-like, trench, and zig-zag shaped boundaries is explained from the energetic point of view. Our study also shows evidence for the superlattice-mediated observation of a low-angle grain boundary with a varying tilt angle. A relationship between the periodicity of the boundary dislocations and the periodicity of the superlattice across the boundary is derived. The result of this work is important for an understanding of superlattices on graphite whose origin is not yet completely understood.