  The capability to control the type and amount of charge carriers in a
material and, in the extreme case, the transition from metal to insulator is
one of the key challenges of modern electronics. By employing angle resolved
photoemission spectroscopy (ARPES) we find that a reversible metal to insulator
transition and a fine tuning of the charge carriers from electrons to holes can
be achieved in epitaxial bilayer and single layer graphene by molecular doping.
The effects of electron screening and disorder are also discussed. These
results demonstrate that epitaxial graphene is suitable for electronics
applications, as well as provide new opportunities for studying the hole doping
regime of the Dirac cone in graphene.
