We demonstrate a novel method to tune the energy gap epsilon1 between the localized states and the mobility edge of the valence band in chemically functionalized graphene by changing the coverage of fluorine adatoms via electron-beam irradiation. From the temperature dependence of the electrical transport properties we show that epsilon1 in partially fluorinated graphene CF0.28 decreases upon electron irradiation up to a dose of 0.08 C cm−2. For low irradiation doses (0.2 C cm−2) the electrical conduction takes place via Mott variable range hopping.SR and MFC acknowledge financial support from EPSRC (grant numbers EP/G036101/1,
EP/J000396/1, EP/K017160/1 and EP/K010050/1). SR acknowledges financial support from
the Royal Society Research grant number 2010/R2 (grant number SH-05052)
