  We have investigated electron dynamics in top gated graphene by measuring the
gate admittance of a diffusive graphene capacitor in a broad frequency range as
a function of carrier density. The density of states, conductivity and
diffusion constant are deduced from the low frequency gate capacitance, its
charging time and their ratio. The admittance evolves from an RC-like to a
skin-effect response at GHz frequency with a crossover given by the Thouless
energy. The scattering time is found to be independent of energy in the 0 - 200
meV investigated range at room temperature. This is consistent with a random
mass model for Dirac Fermions.
