Fig. 3: Construction and characterization of the FeOF membrane enhanced by spatial confinement.

a Schematic illustration of the membrane synthetic protocol. b Cross-sectional FIB-SEM images of the membranes. After the ion beaming, the FeOF was exhausted to leave voids while graphene oxide layers were slightly melted to form a compact surface, featured as a clean cut. c Cross-sectional SEM and SEM-EDS mapping images of the membranes. After the liquid nitrogen cracking, the FeOF between graphene oxide layers could be preserved and the uneven surface favored the observation of layer-by-layer structure, featured as an uneven cracking. d XRD patterns of the membranes. e 2D/3D AFM images of the membranes, where mica was adopted as the substrate (inset: top-view SEM image showing confined FeOF within graphene oxide matrix).