The initial oxidation stages of perfect and defective graphitic surfaces exposed to atomic oxygen have been studied with a combined high-resolution photoemission spectroscopy (HR-PES) and density functional theory (DFT) computational approach. The resulting oxygen-containing surface functional groups are identified by analyzing the multicomponent C 1s and O 1s core level spectra that are then interpreted on the basis of DFT calculations. In the initial oxidation stage, epoxy groups are formed on perfect graphene, whereas the preferential adsorption of the O atoms on the vacancies of the defective surfaces results in structures containing pairs of oxygen atoms in ether and carbonyl (semiquinone) configurations. The formation of these functional groups is preceded by metastable structures consisting of single O atoms occupying single C vacancies.

The performance of new materials and devices often depends on processes taking place at the interface between an active solid element and the environment (such as air, water or other fluids). Understanding and controlling such interfacial processes require surface-specific spectroscopic information acquired under real-world operating conditions, which can be challenging because standard approaches such as X-ray photoelectron spectroscopy generally require high-vacuum conditions. The state-of-the-art approach to this problem relies on unique and expensive apparatus including electron analysers coupled with sophisticated differentially pumped lenses. Here, we develop a simple environmental cell with graphene oxide windows that are transparent to low-energy electrons (down to 400 eV), and demonstrate the feasibility of X-ray photoelectron spectroscopy measurements on model samples such as gold nanoparticles and aqueous salt solution placed on the back side of a window. These proof-of-principle results show the potential of using graphene oxide, graphene and other emerging ultrathin membrane windows for the fabrication of low-cost, single-use environmental cells compatible with commercial X-ray and Auger microprobes as well as scanning or transmission electron microscopes.

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