  Self healing mechanisms of vacancy defects in graphene and silicene are
studied using first principles calculations. We investigated host adatom
adsorption, diffusion, vacancy formation and revealed atomistic mechanisms in
the healing of single, double and triple vacancies of single layer graphene and
silicene. Silicon adatom, which is adsorbed to silicene at the top site forms a
dumbbell like structure by pushing one Si atom underneath. The asymmetric
reconstruction of the single vacancy in graphene is induced by the
magnetization through the rebonding of two dangling bonds and acquiring a
significant magnetic moment through remaining unsaturated dangling bond. In
silicene, three two-fold coordinated atoms surrounding the single vacancy
become four-fold coordinated and nonmagnetic through rebonding. The energy
gained through new bond formation becomes the driving force for the
reconstruction. Under the external supply of host atoms, while the vacancy
defects of graphene heal perfectly, Stone-Wales defect can form in the course
of healing of silicene vacancy. The electronic and magnetic properties of
suspended, single layer graphene and silicene are modified by reconstructed
vacancy defects.
