Fig. 4. Numerical calculations of distributions of ion concentration and electric potential in graphene-based polyethylene terephthalate nanochannel (GPETNC).

a Concentration of potassium ion $c_{{\mathrm{K}}^{+}}$ along the center symmetry axis z of the GPETNC in 0.1 M KCl solution at different voltages. z = 0 and 12 μm represent the tip and base side of the GPETNC, respectively. b Distributions of $c_{{\mathrm{K}}^{+}}$ nearby a graphene subnanopore of the GPETNC in 0.1 M KCl solution at −1 and 1 V. Scale bars are 0.5 nm. c Electric potential ψ at different distances away from the graphene center along a perpendicular path nearby a graphene subnanopore of the GPETNC in 0.1 M KCl solution at −1 and 1 V. The path is 0.75 nm away from the pore center (Supplementary Fig. 8e). The gray dashed lines represent the graphene surfaces in the inner (left) and outer (right) sides of the GPETNC. Δψ indicates the drop between the potential far away from the graphene surface (where ψ hardly changes) and the one on it. d Δψ inner and outer the graphene surface in 0.1 M KCl and CaCl₂ solutions at different voltages.