The role of defects in graphene on the H-terminated SiC surface: Not quasi-free-standing any more

Intercalation of H between the SiC surface and graphene is known to largely reduce the graphene-substrate interaction thus leaving a so called quasi-free-standing graphene monolayer (QFG) which preserves most of the properties of free-standing graphene (FG). Here, we investigate via large-scale density functional theory (DFT) based calculations point defects in FG and QFG in the form of single vacancies passivated by additional H atoms. For QFG our results reveal that the intercalated H layer interacts strongly with the defects attracting unsaturated C atoms but repelling the H-passivated ones thus leading to large reconstructions which, in turn, may induce drastic changes on the electronic and magnetic properties when compared against FG. We conclude that QFG with defect concentrations larger than 0.3% cannot be regarded in general as quasi-free-standing any more.