  Realization of a free-standing graphene is always a demanding task. Here we
use scanning probe microscopy and spectroscopy to study the crystallographic
structure and electronic properties of the uniform free-standing graphene
layers obtained by intercalation of oxygen monolayer in the "strongly" bonded
graphene/Ru(0001) interface. Spectroscopic data show that such graphene layer
is heavily p-doped with the Dirac point located at 552 meV above the Fermi
level. Experimental data are understood within DFT and the observed effects are
in good agreement with the theoretical data.
