Giant surface charge density of graphene resolved from scanning tunneling microscopy and first-principles theory

In this work, systematic constant-bias, variable-current scanning tunneling microscopy (STM) measurements and STM simulations from density-functional theory are carried out, yielding critical insights into the spatial structure of electrons in graphene. A foundational comparison is drawn between graphene and graphite, showing the surface charge density of graphene to be 300% that of graphite. Furthermore, simulated STM images reveal that high-current STM better resolves graphene's honeycomb bonding structure because of a retraction which occurs in the topmost dangling bond orbitals. © 2011 American Physical Society.