Irradiation of graphene on ${\mathrm{SiO}}_2$ by 500 eV Ne and He ions creates defects that cause intervalley scattering as is evident from a significant Raman $D$ band intensity. The defect scattering gives a conductivity proportional to charge carrier density, with mobility decreasing as the inverse of the ion dose. The mobility decrease is 4 times larger than for a similar concentration of singly charged impurities. The minimum conductivity decreases proportional to the mobility to values lower than $4e^2/\pi h$, the minimum theoretical value for graphene free of intervalley scattering. Defected graphene shows a diverging resistivity at low temperature, indicating insulating behavior. The results are best explained by ion-induced formation of lattice defects that result in midgap states.

• Received 23 March 2009

DOI:https://doi.org/10.1103/PhysRevLett.102.236805