The adsorption and reaction of O₂ with defects on graphene/Ru(0001)

Small molecules, such as O₂ and CO_, can intercalate between deposited graphene (Gr) and a substrate, and can also etch the Gr overlayer when it is heated to desorb the intercalates. The experiments performed here employ Gr grown on Ru(0001) by chemical vapor deposition into which single carbon vacancy defects are formed by Ar⁺ bombardment. A new adsorption site is identified on the surface of defected graphene and it is shown that these defects also affect the intercalation and etching process. The surfaces are interrogated with low energy helium ion scattering, which can monitor the adsorption and intercalation of oxygen and the etching of the graphene. The scattering angle is adjusted so that adatoms attached to the Gr surface can be distinguished from the intercalates. It is found that the oxygen deposited at room temperature at a carbon vacancy is adsorbed at a unique site and is not directly bonded to the Ru substrate. Moreover, the defects ease the intercalation of O₂ and improve the etching efficiency during annealing, while the magnitude of this effect depends on the size of the defects.