Vacancy creation in graphene-based materials explored with scanning tunnelling microscopy*

Ion bombardment is a powerful tool for generating point defects in two-dimensional materials. Particularly interesting are single atom vacancies which, as is the case in graphene, carry a charge that can become super-critical and exhibit atomic collapse. Furthermore, vacancies in graphene carry a local magnetic moment which, in the presence of local curvature, can be Kondo screened by the conduction electrons. Here we study the nature of vacancies and the electronic response to their presence in a variety of 2D samples including graphene-based materials, by varying ion species, ion energy and exposure times. We use scanning tunneling microscopy, scanning tunneling spectroscopy, and Landau Level spectroscopy in high magnetic field to characterize the effects of ion bombardment on the interlayer coupling and the electronic and magnetic properties of the vacancies.