  We report the hydrogenation of single and bilayer graphene by an
argon-hydrogen plasma produced in a reactive ion etching (RIE) system.
Electronic transport measurements in combination with Raman spectroscopy are
used to link the electric mean free path to the optically extracted defect
concentration. We emphasize the role of the self-bias of the graphene in
suppressing the erosion of the akes during plasma processing. We show that
under the chosen plasma conditions the process does not introduce considerable
damage to the graphene sheet and that hydrogenation occurs primarily due to the
hydrogen ions from the plasma and not due to fragmentation of water adsorbates
on the graphene surface by highly accelerated plasma electrons. For this reason
the hydrogenation level can be precisely controlled. The hydrogenation process
presented here can be easily implemented in any RIE plasma system.
