Coordination-Resolved C-C Bond Length and the C 1s Binding Energy of Carbon Allotropes and the Effective Atomic Coordination of the Few-Layer Graphene

Binding energy variation due to the change of atomic coordination has formed the key to the different fascinating properties of carbon allotropes such as graphene nanoribbons, carbon nanotubes, graphite, and diamond. However, determination of the binding energies of these allotropes with a consistent understanding of the effect of bond order variation on the binding energy change has long been a great challenge. Here we show that a combination of the bond order-length-strength correlation theory (Sun, C. Q. Prog. Solid State Chem. 2007, 35, 1) and the photoelectron emission technique has enabled us to quantify the Cis binding energy of atomic carbon and its shift upon carbon allotrope formation. It has been confirmed that the C-C bond contracts spontaneously by up to 30% at the edges of graphene ribbons with respect to the bulk-diamond value of 0.154 nm. The Cis energy shifts positively by values from 1.32 eV for bulk diamond to 3.33 eV for graphene edges with respect to that of 282.57 eV for an isolated carbon atom. The calibration using the bond order-length-strength solution has also enabled estimation of the effective atomic coordination of the few-layer graphene, which is critical for further investigations such as the layer-resolved Raman shift.