Preferential antiferromagnetic coupling of vacancies in graphene on SiO2: Electron spin resonance and scanning tunneling spectroscopy

ion bombardment at a kinetic energy of 50 eV. The density of defectsvisible in scanning tunneling microscopy (STM) is considerably lower than the ion uence implyingthat most of the defects are single vacancies. The vacancies are characterized by scanning tunnelingspectroscopy (STS) on graphene and HOPG exhibiting a peak close to the Fermi level. The peakpersists after air exposure up to 180 min, albeit getting broader. After air exposure for less than60 min, electron spin resonance (ESR) at 9.6 GHz is performed. For an ion ux of 10/nm