Direct observation of graphite layer edge states by scanning tunneling microscopy

The electronic and structural properties of two different edge terminations in normal graphite layer edges were investigated at atomic resolution using scanning tunneling microscopy (STM)and electronic band structure calculations. An emphasis is placed on distinguishing the electronic structure of [1,1,(2) over bar ,0] (''armchair'') and [1,0,(1) over bar ,0] (''zigzag'') edge terminations. Experimental STM investigations reveal that the [1,1,2,0] termination exhibits a(root 3x root R30 degrees superstructure in the local electron density of states profile superimposed on the normal graphite lattice. The [1,0,(1) over bar ,0] edge shows a different superstructure typified by two to three atomic lattice cells of high electron density parallel to the edge. The armchair edge superstructure persists for 2-3 nm (equivalent to about 10 unit cells) into the bulk layer. By modeling these edge types using extended Huckel tight binding calculations, we show that the results are consistent with an unreconstructed edge geometry. The details of the edge states do not appear to be particularly sensitive to the chemical composition of the edge. The experimental results are in general agreement with previously reported modeling studies of these edge states. (C) 2001 American Institute of Physics.