Fig. 4

Additional structural features of permeable graphene films. Additional characterisation of the graphene films reveals their rough surface texture and variation in thickness. These features are favourable for generating a bottleneck region for water vapour permeation. The presence of multiple nanocrystalline domains suggests the existence of numerous channels for water vapour permeation. a An AFM topography image of the edge of a graphene film deposited on a mica substrate; the dark region at the left hand side of the image is the mica substrate; the lighter region is the graphene film; and the bright spots are most likely residue from the wet-transfer process; scale bar is 1 µm. b A relative height histogram of the AFM image (a). The high narrow peak around 0 nm height represents the mica substrate, the broader distribution represents the graphene film and the tail up to heights of 18 nm most likely represents wet-transfer process residue. c, d Raman spectral mapping analyses of the intensity ratios of I_D/I_G and I_2D/I_G