  Tunable and highly reproducible metal-insulator transitions have been
observed in bilayer graphene upon thermal annealing at 400 K under high vacuum
conditions. Before annealing, the sample is metallic in the whole temperature
regime of study. Upon annealing, the conductivity changes from metallic to that
of an insulator and the transition temperature is a function of annealing time.
The pristine metallic state can be reinstated by exposing to air thereby
inducing changes in the electronic properties by adsorbing water vapor, which
makes graphene a technologically promising material for sensor applications.
