  The temperature dependence of electric transport properties of single-layer
and few-layer graphene at large charge doping is of great interest both for the
study of the scattering processes dominating the conductivity at different
temperatures and in view of the theoretically predicted possibility to reach
the superconducting state in such extreme conditions. Here we present the
results obtained in 3-, 4- and 5-layer graphene devices down to 3.5 K, where a
large surface charge density up to about 6.8x10^14 cm^(-2) has been reached by
employing a novel polymer electrolyte solution for the electrochemical gating.
In contrast with recent results obtained in single-layer graphene, the
temperature dependence of the sheet resistance between 20 K and 280 K shows a
low-temperature dominance of a T^2 component - that can be associated with
electron-electron scattering - and, at about 100 K, a crossover to the classic
electron-phonon regime. Unexpectedly this crossover does not show any
dependence on the induced charge density, i.e. on the large tuning of the Fermi
energy.
