  Combining scanning tunneling microscopy and angle-resolved photoemission
spectroscopy, we demonstrate how to tune the doping of epitaxial graphene from
p to n by exploiting the structural changes that occur spontaneously on the Ge
surface upon thermal annealing. Furthermore, using first principle calculations
we build a model that successfully reproduces the experimental observations.
Since the ability to modify graphene electronic properties is of fundamental
importance when it comes to applications, our results provide an important
contribution towards the integration of graphene with conventional
semiconductors.
