Irradiation of graphene on SiO2 by 500 eV Ne and He ions creates defects that cause intervalley scattering as 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 four 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 mid-gap states.
@article{arxiv.0903.2602,
title = {Defect scattering in graphene},
author = {Jian-Hao Chen and W. G. Cullen and C. Jang and M. S. Fuhrer and E. D. Williams},
journal= {arXiv preprint arXiv:0903.2602},
year = {2009}
}