Manipulation of the graphene surface potential by ion irradiation

We show that the work function of exfoliated single layer graphene can be modified by irradiation with swift (Ekin=92 MeV) heavy ions under glancing angles of incidence. Upon ion impact individual surface tracks are created in graphene on silicon carbide. Due to the very localized energy deposition characteristic for ions in this energy range, the surface area which is structurally altered is limited to ≈0.01 μm2 per track. Kelvin probe force microscopy reveals that those surface tracks consist of electronically modified material and that a few tracks suffice to shift the surface potential of the whole single layer flake by ≈400 meV. Thus, the irradiation turns the initially n-doped graphene into p-doped graphene with a hole density of 8.5×1012 holes/cm2. This doping effect persists even after heating the irradiated samples to 500 °C. Therefore, this charge transfer is not due to adsorbates but must instead be attributed to implanted atoms. The method presented here opens up a way to efficiently manipulat...