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Zusammenfassung

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.