  We study the effects of low-energy electron beam irradiation up to 10 keV on
graphene based field effect transistors. We fabricate metallic bilayer
electrodes to contact mono- and bi-layer graphene flakes on SiO$_2$, obtaining
specific contact resistivity $\rho_c \simeq 19 k\Omega \mu m^2$ and carrier
mobility as high as 4000 cm$^2$V$^{-1}$s$^{-1}$. By using a highly doped
p-Si/SiO$_2$ substrate as back gate, we analyze the transport properties of the
device and the dependence on the pressure and on the electron bombardment. We
demonstrate that low energy irradiation is detrimental on the transistor
current capability, resulting in an increase of the contact resistance and a
reduction of the carrier mobility even at electron doses as low as 30
$e^-/nm^2$. We also show that the irradiated devices recover by returning to
their pristine state after few repeated electrical measurements.
