Discriminative generation and hydrogen modulation of the Dirac-Fermi polarons at graphene edges and atomic vacancies

Using a combination of the bond order-length-strength correlation theory, the spin-polarized tight binding method, the first-principles calculations, and the atomistic photoelectron distillation experiments, we investigated the mechanisms of edge-selective generation and hydrogenated modulation of Dirac-Fermi polarons (DFPs) surrounding the atomic vacancies at a graphite surface and at the edges of graphene nanoribbons (GNR). We found that: (i) the DFPs with a high-spin density at a zigzag-GNR edge and at an atomic vacancy result from the isolation and polarization of the dangling a-bond electrons of root 3d (d is the C-C bond length) distance along the edge by the locally and densely entrapped bonding electrons; (ii) along an armchair-GNR edge and a reconstructed-zigzag-GNR edge, however, the formation of quasi-triple-bond between the nearest edge atoms of d distance prevents the DFPs from generation; and (iii) hydrogenation reduces the spin density substantially and turns the asymmetric dumb-bell-like density into the spherical-like p(z) density. A further C 1s photoelectron spectroscopic purification has confirmed that the generation of the DFPs is associated with two extra peaks of energy states located at the bottom and the top edge of the C 1s band. (C) 2011 Elsevier Ltd. All rights reserved.