Atomically resolved imaging of highly ordered alternating fluorinated graphene

One of the most desirable goals of graphene research is to produce ordered two-dimensional (2D) chemical derivatives of suitable quality for monolayer device fabrication. Here we reveal, by focal series exit wave reconstruction (EWR), that C₂F chair is a stable graphene derivative and demonstrates pristine long-range order limited only by the size of a functionalized domain. Focal series of images of graphene and C₂F chair formed by reaction with XeF₂ were obtained at 80kV in an aberration-corrected transmission electron microscope. EWR images reveal that single carbon atoms and carbon-fluorine pairs in C₂F chair alternate strictly over domain sizes of at least 150nm² with electron diffraction indicating ordered domains ≥ 0.16 μm². Our results also indicate that, within an ordered domain, functionalization occurs on one side only as theory predicts. In addition, we show that electron diffraction provides a quick and easy method for distinguishing between graphene, C₂F chair and fully fluorinated stoichiometric CF 2D phases.