  We report a stoichiometric derivative of graphene with a fluorine atom
attached to each carbon. Raman, optical, structural, micromechanical and
transport studies show that the material is qualitatively different from the
known graphene-based nonstoichiometric derivatives. Fluorographene is a
high-quality insulator (resistivity >10^12 Ohm per square) with an optical gap
of 3 eV. It inherits the mechanical strength of graphene, exhibiting Young's
modulus of 100 N/m and sustaining strains of 15%. Fluorographene is inert and
stable up to 400C even in air, similar to Teflon.
