  Graphene is one of the most promising 2D materials for various applications
due to its unique electronic properties and high thermal stability. In previous
studies, it was shown that when graphene is deposited onto some transition
metal substrates, small molecules, such as O$_2$, intercalate between the
graphene and the substrate and react to partially etch the graphene film when
heated to desorb the intercalates. Here, carbon vacancy defects are
intentionally formed on Gr/Ru(0001) and their effect on the intercalation of
oxygen and etching of the graphene layer are investigated. 50 eV Ar$^+$
sputtering with a low fluence is used to create isolated single vacancy defects
in the graphene overlayer and helium low energy ion scattering (LEIS) is
employed for surface analysis. It is found that the defects both ease the
intercalation of the oxygen molecules and improve the etching efficiency of the
graphene during annealing.
