Reversible photon-induced oxidation of graphene by NO2 adsorption

We show that an oxidized graphene sheet is formed by NO2 adsorption and subsequent photodissociation, through an analysis of X-ray absorption and photoemission spectroscopic results. Adsorption of NO2 on graphene grown on Ir(111) leads to a strong rehybridization of the unoccupied π* states and the appearance of new features in the C 1s core level line. This is a reversible process, such that pristine graphene can be recovered by thermal treatment. The formation of oxidized graphene is sensitive to the photon-flux, resulting in an intermediate phase of oxidized graphene. Our results provide an interesting pathway towards lithographic patterning processes in graphene.