  We show that the low temperature electron transport properties of chemically
functionalized graphene can be explained as sequential tunneling of charges
through a two dimensional array of graphene quantum dots (GQD). Below 15 K, a
total suppression of current due to Coulomb blockade through GQD array was
observed. Temperature dependent current-gate voltage characteristics show
Coulomb oscillations with energy scales of 6.2-10 meV corresponding to GQD
sizes of 5-8 nm while resistance data exhibit an Efros-Shklovskii variable
range hopping arising from structural and size induced disorder.
