Non-thermal and low-destructive X-ray induced graphene oxide reduction

Large-scale graphene fabrication by thermal and chemical reductions of graphene oxide has faced the problem of defect formation. To solve the problem, we have considered a physically alternative reduction process including electronic excitation followed by the oxygen group detachment from the carbon sheet without capturing a sheet of carbon atoms. Single-layer graphene oxide films were studied by photoemission spectroscopy in the course of monochromatic synchrotron X-ray radiation with in situ control of the layer thickness, chemical composition, atomic ordering, and defect concentration exactly in the modified area. The radiation flux was too low to heat the film. A non-thermal and low-destructive effect of X-ray induced graphene oxide reduction has been revealed. Transformation of the sp³ σ bonds into sp² π ordered bonds, bandgap closing, and significant diminishing of the oxygen content (below 5 at. %) have been observed without any signs of defects in the photoemission spectra. The effective cross section of the oxygen group detachment induced by a soft X-ray photon (hν = 130 eV) was estimated to be σ* ∼ 3 × 10⁻¹⁸ cm². A reduced single-layer graphene oxide with a narrow bandgap (0.4 – 0.8 eV) attractive for many applications was obtained, as well as almost pure graphene.