Reversible oxidation states of single layer graphene tuned by electrostatic potential

We report the reversible oxidation and reduction of single layer graphene on a self-aligned Cu-rich CuOx layer, which was created on a Cu substrate by thermal reduction of a native Cu-oxide layer while forming graphene on top of the Cu by chemical vapor deposition. The reversible oxidation states of graphene, revealed by X-ray photoemission and Raman spectroscopies, were driven by migration of oxygen ions in the CuOx layer under external electrostatic bias. Breaking the translational symmetry of the CC sp2 bonds by the migrated oxygen resulted in a noticeable D band peak in the Raman spectra. However, the D band peak was not completely reduced under reverse external bias, indicating a certain level of permanent oxygen bonding on the graphene. First-principles density functional theory calculations suggested two distinct grapheneoxygen bonding configurations i.e., (1) a most-stable epoxy-like bridged oxygen and (2) a meta-stable ketone-like on-top oxygen in a four-membered ring configuration, which might be responsible for the irreversible and reversible oxidation states of graphene, respectively.