Charging and discharging of graphene in ambient conditions studied with scanning probe microscopy

By means of scanning probe microscopy we are able to inject charges in isolated graphene sheets deposited on SiO(2)/Si wafers and characterize the discharge induced by water in controlled ambient conditions. Contact potential differences between the graphene surface and the probe tip, measured by Kelvin probe microscopy, show a linear relationship with the tip bias during charge injection. The discharge depends on relative humidity and decays exponentially with time constants of the order of tens of minutes. We propose that graphene discharges through the water film adsorbed on the SiO(2) surface.