Zone-selective photoelectronic measurements of the local bonding and electronic dynamics associated with the monolayer skin and point defects of graphite

Abstract

Zone-resolved photoelectron spectroscopy (ZPS) has enabled us to gain local and quantitative information (and hence confirm our theoretical expectations) on the bonding and electronic dynamics associated with the monolayer skin and atomic vacancy defects of graphite. The ZPS revealed: (i) the 1s energy level of an isolated carbon atom is located at 282.57 eV, which increases by 1.32 eV upon diamond bulk formation; (ii) the graphite surface bonds contract by 18% with a 165% gain in energy compared with a C–C bond in bulk diamond; the surface C 1s energy increases by 2.08 eV from the 1s level of an isolated carbon atom; and (iii) the defect bonds are 26% shorter and 215% stronger with a binding energy shift of 2.85 eV. An additional polarization peak centered at 1.28 eV below the C 1s level is present when a vacancy is formed. In association with the scanning tunneling microscopy/spectroscopy observations and density functional theory calculations, the ZPS measurements clarify, for the first time, that the graphitic Dirac–Fermi polarons at an atomic vacancy or on graphene’s zigzag edge arise from the polarization of the unpaired dangling-bond electrons by the under-coordination-induced local densification and quantum entrapment of the bonding electrons. The theory-enabled ZPS complements scanning tunneling microscopy/spectroscopy and conventional photoelectron emission techniques in understanding the bond and electronic dynamics at the atomic scale.