Direct observation of graphite layer edge states by scanning tunneling microscopy

Abstract

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 [1,1,2̄,0] (“armchair”) and [1,0,1̄,0] (“zigzag”) edge terminations. Experimental STM investigations reveal that the [1,1,2̄,0] termination exhibits a (3×3)R30° superstructure in the local electron density of states profile superimposed on the normal graphite lattice. The [1,0,1̄,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 Hückel 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.

Mean-field resonance-theoretic view of benzenoid networks

“…Again this is an extreme approximation as to spin-density location, with it reasonably being that there is some delocalization of the unpaired electrons (or spin density) a little into the region near the boundary (but remaining largely on the same type of sites) with the net unpaired spin density being 1/3 of an electron per unit cell of edge. Also again this prediction seems to be perfectly correct from different theoretical schemes 24,60,61 , with there also being supporting experimental evidence from tunnelling electron microscopy 62 .…”

Scanning tunneling microscopy and spectroscopy of the electronic local density of states of graphite surfaces near monoatomic step edges

“…Scanning tunneling microscopy (STM) measurements have been performed at linear step edges at the surface of highly oriented pyrolytic graphite (HOPG). 11,12 So far, the (…”

“…11,12 Here, we investigated the LDOS in the vinicity of linear step edges of both the zigzag and armchair types with STM/STS. A Brief Report of the STS observation of the graphite edge state has been already made elsewhere.…”

Half-Metallic Zigzag Carbon Nanotube Dots

“…[18][19][20][21][22][23][24][25][26][27][28][29]42,[45][46][47][48][49][50][51][52] When cutting a graphene sheet along its zigzag axis to form a narrow and elongated graphene nanoribbon (GNR), distinct electronic states appear, which are localized around the exposed edges. [54][55][56][57][58][59] These states are predicted to carry spin polarization, resulting in a well defined magnetic ordering. [19][20][21][22][23][24][25][26]28,29,42,[45][46][47][48][49][50][51][52] Due to the bipartite hexagonal structure of graphene, the electronic ground state of such zigzag graphene nanoribbons (ZZ-GNRs) is characterized by an antiferromagnetic (AFM) spin ordering, where the edge states located at the two zigzag edges of the ribbon have opposite spins.…”